Evoked Potential Studies
Number: 0181
Table Of Contents
PolicyApplicable CPT / HCPCS / ICD-10 Codes
Background
References
Policy
Scope of Policy
This Clinical Policy Bulletin addresses evoked potential studies.
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Medical Necessity
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Evoked Potential Studies
Aetna considers evoked potential studies medically necessary for the following indications
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Somatosensory evoked potentials (SEPs, SSEPs) or dermatosensory evoked potentials (DSEPs)
Considered medically necessary for any of the following indications:
- To assess any decline which may warrant emergent surgery in unconscious spinal cord injury persons who show specific structural damage to the somatosensory system, and who are candidates for emergency spinal cord surgery; or
- To evaluate acute anoxic encephalopathy (within 3 days of the anoxic event); or
- To evaluate persons with suspected brain death; or
- To identify clinically silent brain lesions in multiple sclerosis suspects in order to establish the diagnosis, where multiple sclerosis is suspected due to presence of suggestive neurologic symptoms plus one or more other objective findings (brain plaques on MRI, clinical lesions by history and physical examination, and/or positive CSF (determined by oligoclonal bands detected by established methods (isoelectric focusing) different from any such bands in serum, or by an increased IgG index)); or
- To localize the cause of a central nervous system deficit seen on exam, but not explained by lesions seen on CT or MRI; or
- To manage persons with spinocerebellar degeneration (e.g., Friedreichs ataxia, olivopontocerebellar (OPC) degeneration); or
- Unexplained myelopathy, or
- Intraoperative SSEPs under certain conditions (see I. B., below).
SEPs and DSEPs are considered experimental and investigational for all other indications because their effectiveness for indications other than the ones listed above has not been established.
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Intraoperative somatosensory evoked potentials (SSEPs) performed either alone, or in combination with motor evoked potentials (MEPs)
Considered medically necessary for monitoring the integrity of the spinal cord to detect adverse changes before they become irreversible during spinal, intracranial, orthopedic, or vascular procedures, when the following criteria are met:
- A specially trained physician or a certified professional practicing within the scope of their license, who is not a member of the surgical team contemporaneously interprets the intraoperative evoked potentials during the operation; and
- The evoked potential monitoring is performed in the operating room by dedicated trained technician; and
- The clinician who performs the interpretation is monitoring no more than 3 surgical procedures at the same time; and
- The clinician who performs the interpretation may do so remotely, but must provide direct, immediate communication of intraoperative evoked potential results to the technician and surgeon during the operation.
Intraoperative SEP monitoring, with or without MEPs, may be appropriate for the following types of surgery (not an all-inclusive list):
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Spinal Surgeries
- Correction of scoliosis or deformity of the spinal cord involving traction on the cord
- Decompression of the spinal cord where function of the spinal cord is at risk
- During incision and drainage of paraspinal/epidural abscess of cervical spine
- During invasive spinal rod lengthening
- Removal of spinal cord tumors (including sacral tumors)
- Surgery as a result of traumatic injury to the spinal cord
- Surgery for arteriovenous (AV) malformation of the spinal cord
- Tethered cord release
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Intracranial Surgeries
- Chiari malformation surgery
- Correction of cerebral vascular aneurysms (e.g., cerebral aneurysm clipping, coil embolization)
- Deep brain stimulation
- Endolymphatic shunt for Meniere's disease
- Microvascular decompression of cranial nerves (e.g., optic, trigeminal, facial, auditory nerves)
- Oval or round window graft
- Removal of cavernous sinus tumors
- Removal of tumors that affect cranial nerves
- Resection of brain tissue close to the primary motor cortex and requiring brain mapping
- Resection of epileptogenic brain tissue or tumor
- Surgery as a result of traumatic injury to the brain
- Surgery for intracranial AV malformations
- Surgery for intractable movement disorders
- Surgery for moyamoya disease
- Vestibular section for vertigo
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Vascular Surgeries
- Arteriography, during which there is a test occlusion of the carotid artery
- Circulatory arrest with hypothermia (does not include surgeries performed under circulatory bypass such as CABG, and ventricular aneurysms)
- Distal aortic procedures, where there is risk of ischemia to the spinal cord
- Surgery of the aortic arch, its branch vessels, or thoracic aorta, including carotid artery surgery (e.g., carotid endarterectomy), when there is risk of cerebral ischemia.
Intra-operative SSEPs with or without MEPs are considered experimental and investigational for all other indications (e.g., scapula-thoracic fusion surgery) because their effectiveness for indications other than the ones listed above has not been established.
Note: Depending on the clinical condition being investigated, it may be medically necessary to test several nerves in one extremity and compare them with the opposite limb.
Note: Intra-operative evoked potential studies have no proven value for lumbar surgery below (distal to) the end of the spinal cord; the spinal cord ends at L1-L2.
Note: Post-operative SEP or MEP monitoring is not considered medically necessary for individuals who have undergone intra-operative SEP or MEP monitoring.
Note: The NIM-Spine System received 510(k) clearance from the Food and Drug Administration (FDA) in June 2003. It offers 2 types of monitoring modalities: electromyography and MEP.
Note on documentation requirements: The physician's SEP report should note which nerves were tested, latencies at various testing points, and an evaluation of whether the resulting values are normal or abnormal. See appendix for additional details on documentation requriements.
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Visual Evoked Potentials (VEPs)
Considered medically necessary for any of the following indications:
- To diagnose and monitor multiple sclerosis (acute or chronic phases); or
- To evaluate signs and symptoms of visual loss in persons who are unable to communicate (e.g., unresponsive persons, etc); or
- To identify persons at increased risk for developing clinically definite multiple sclerosis (CDMS); or
- To localize the cause of a visual field defect, not explained by lesions seen on CT or MRI, metabolic disorders, or infectious diseases.
Standard or automated VEPs are considered experimental and investigational for routine screening of infants and other persons; evidence-based guidelines from leading medical professional organizations and public health agencies have not recommended VEP screening of infants. VEPs are considered experimental and investigational for all other indications because their effectiveness for indications other than the ones listed above has not been established.
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Brain Stem Auditory Evoked Response (BAER)
Footnote1** Considered medically necessary for any of the following:
- For cerebral vascular surgery; or
- For Chiari malformation surgery; or
- For intra-operative monitoring during microvascular decompression of cranial nerve when decompression is performed via the intra-cranial posterior fossa approach; or
- For intra-operative monitoring during resection of chordoma , odontoidectomy, decompression of tumor from anterior brainstem/high spinal cord; or
- For intra-operative monitoring of other surgeries involving the posterior fossa (including resection of pineal mass) to help assess brainstem function and preserve hearing; or
- To assess brain death or profound metabolic coma in selected cases where diagnosis or outcome is unclear from standard tests (e.g., EEG); or
- To assess recovery of brainstem function after a lesion compressing the brainstem has been surgically removed; or
- To diagnose and monitor demyelinating and degenerative diseases affecting the brain stem (e.g., central pontine myelinolysis, olivopontocerebellar (OPC) degeneration, etc.); or
- To diagnose post-meningitic deafness in children; or
- To diagnose suspected acoustic neuroma; or
- To evaluate infants and children who have suspected hearing loss that cannot be effectively measured or monitored through audiometry; or
- To localize the cause of a central nervous system deficit seen on examination, but not explained by CT or MRI; or
- To screen infants and children under 3 years of age for hearing loss.
Note: For purposes of screening (including neonatal screening), only limited auditory evoked potentials or limited evoked otoacoustic emissions (OAE) are considered medically necessary. Neonates, infants and children under 3 years of age who fail this screening test are then referred for comprehensive auditory evoked response testing or comprehensive otoacoustic emissions. Comprehensive auditory evoked response testing and comprehensive otoacoustic emissions are considered experimental and investigational for initial screening because there is a lack of evidence of the value of comprehensive testing over the limited auditory evoked potentials or limited otoacoustic emissions for this indication.
Note: Routine evoked OAE screening at a well-child visit is not considered medically necessary for children 3 years of age and younger who have passed the newborn hearing screen unless the child has a risk factor for hearing loss, has impairment of speech or auditory skills, or has an abnormal middle ear status. Evoked OAE is considered medically necessary to screen children 3 years of age and younger who did not have the initial neonatal screening and/or cannot be effectively measured or monitored through audiometry.
BAERs are considered experimental and investigational for all other indications because their effectiveness for indications other than the ones listed above has not been established.
Footnote1**Also known as auditory brainstem response (ABR), auditory evoked potentials (AEPs), brainstem auditory evoked potentials (BAEP), BERA, BSER, and BSRA.
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Cervical Vestibular Evoked Myogenic Potential (cVEMP)
Aetna considers cervical vestibular evoked myogenic potential (cVEMP) medically necessary for the evaluation of individuals with vertigo for semicircular canal dehiscence syndrome (SCDS) who have had a comprehensive evaluation (i.e., history, physical, audiometry, electronystagmography or videonystagmography, electrocochleography, brainstem audiometry) and the results are inconclusive.
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Intra-Operative Neuromonitoring (IONM) During Lower Extremity and Buttock Reconstruction
Aetna considers intra-operative neuromonitoring (IONM) medically necessary during eligible lower extremity and buttock reconstruction.
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Experimental and Investigational
The following procedures are considered experimental and investigational because the effectiveness of these approaches has not been established:
- Auditory evoked potentials during surface electroencephalography (sEEG) implantation into the brain cortex;
- Auditory evoked potential monitoring during cochlear implantation;
- Auditory evoked potential for evaluation of hearing and language deficits in survivors of extracorporeal membrane oxygenation;
- Auditory evoked potential to determine gestational age or conceptual age in pre-term neonates;
- BAERs as a test to identify persons at increased risk for developing clinically definite multiple sclerosis (CDMS);
- BAERs for syringomyelia and syringobulbia;
- Cervical vestibular evoked myogenic potentials (cVEMP) for evaluation of vestibular function specifically related to the saccule/utricle;
- cVEMP for the diagnosis of benign paroxysmal positional vertigo, and vestibular neuritis;
- Cognitive evoked potentials (also known as auditory or visual P300 or P3 cognitive evoked potentials) to diagnose cognitive dysfunction in persons with dementia (e.g., Alzheimer's disease and Parkinson's disease) or to identify the etiology of depression in persons with chronic demyelinating disease;
- Cortical auditory evoked response (CAER) for the diagnosis of depression, attention deficit/hyperactivity disorder, autism, or any other indication;
- Event-related potentials for the diagnosis of attention deficit/hyperactivity disorder (see CPB 0426 - Attention Deficit/Hyperactivity Disorder) or post-traumatic stress disorder, or assessment of amyotrophic lateral sclerosis, brain injury, or evaluation of comatose persons;
- Evoked potential monitoring during degenerative cervical spine surgery;
- Evoked potential studies for Kennedy's syndrome/disease;
- Gustatory evoked potentials for diagnosing taste disorders (see CPB 0390 - Smell and Taste Disorders: Diagnosis);
- Intraoperative BAER during stapedectomy, tympanoplasty and ossicle reconstruction;
- Intraoperative MEP during implantation of a spinal cord stimulator;
- Intraoperative neuromonitoring during carpal tunnel release;
- Intraoperative neuromonitoring during cervical lymphadenectomy (modified radical neck dissection);
- Intraoperative neuromonitoring during craniotomy repair of cerebrospinal fluid leak;
- Intraoperative neuromonitoring during femur, tibia/fibula osteotomy and ankle arthrodesis;
- Intraoperative neuromonitoring during femoroacetabular surgery;
- Intraoperative neuromonitoring during implantation, removal, and adjustment of vertical expandable prosthetic titanium rib (VEPTR);
- Intraoperative neuromonitoring during lymph node biopsy;
- Intraoperative neuromonitoring during removal of spinal cord stimulator;
- Intraoperative neuromonitoring during resection of a middle ear mass;
- Intraoperative neuromonitoring during rib resection;
- Intraoperative neuromonitoring during rotator cuff repair;
- Intraoperative neuromonitoring during sacretomy;
- Intraoperative neuromonitoring during sacroiliac joint fusion;
- Intraoperative neuromonitoring during scalenectomy;
- Intraoperative neuromonitoring during sciatic nerve biopsy;
- Intraoperative neuromonitoring during sciatic nerve tumor removal;
- Intraoperative neuromonitoring during shoulder surgery;
- Intraoperative neuromonitoring during spinal cord stimulator placement and removal;
- Intraoperative neuromonitoring during stapedectomy/ossicular chain reconstruction;
- Intraoperative neuromonitoring during surgery for the correction of thoracic outlet syndrome;
- Intraoperative neuromonitoring during surgery for the treatment of priformis syndrome;
- Intraoperative neuromonitoring during thoracotomy for resection of mediastinal mass (unless the mass is around the spinal cord or it involves the aorta or the radicular arteries branching off the aorta);
- Intraoperative neuromonitoring during thyroidectomy and thyroid re-operations;
- Intraoperative neuromonitoring during total knee arthroplasty;
- Intraoperative neuromonitoring during total hip replacement;
- Intraoperative neuromonitoring during Zenkers diverticulectomy;
- Intraoperative neuromuscular junction testing in member with anoxic brain injury;
- Intraoperative saphenous nerve somatosensory evoked potential for monitoring the femoral nerve during transpoas lumbar lateral interbody fusion;
- Intraoperative SSEP monitoring during hip dysplasia and labral repair surgery;
- Intraoperative SSEP during open reduction internal fixation of acetabulum fracture;
- Intraoperative SSEP during transforaminal epidural steroid injections;
- Intraoperative SSEP of the facial nerve for submandibular gland excision or parotid gland surgery, during hip replacement surgery, implantation of a spinal cord stimulator, off-pump coronary artery bypass surgery, and for thyroid surgery and parathyroid surgery (because they have not been proven necessary to aid in diagnosis or alter the management of individual undergoing surgical treatment);
- Intraoperative SSEP, with or without MEPs, for cochlear implantation, implantation of vagus nerve stimulator, monitoring spinal injections (e.g., epidural injections, facet joint, interlaminar and transforminal epidural), open reduction internal fixation (ORIF) of the finger, radiofrequency ablation of facet medial branch, rotator cuff repair, or wrist arthroscopy repair;
- Intraoperative visual evoked potentials (e.g., for pituitary surgery, during intra-cranial surgery for arterio-venous malformation);
- Loudness dependence of auditory evoked potentials for monitoring of suicidal persons;
- Motor evoked potentials for evaluation of Wilson's disease;
- Motor evoked potential monitoring for peripheral nerve ablation;
- Motor evoked potentials other than for intraoperative use with SSEPs (e.g., facial MEPs during cerebellopontine angle and skull base tumor surgery);
- Ocular vestibular evoked myogenic potentials (oVEMP) for the diagnosis of benign paroxysmal positioning vertigo, myasthenia gravis, or vestibular neuritis;
- Ocular vestibular evoked myogenic potentials (oVEMP) for the evaluation of vestibular function specifically related to the saccule/utricle;
- Olfactory event‐related potential for the evaluation of long-term COVID-19;
- Pre-operative SSEP of the bilateral tibial somatosensory pathways prior to scoliosis surgery;
- SEPs monitoring during trigger point injection for management of low back pain;
- SEPs for radiculopathies and peripheral nerve lesions where standard nerve conduction velocity studies are diagnostic (see CPB 0502 - Nerve Conduction Studies);
- SEPs for the diagnosis of carpal tunnel syndrome/ulnar nerve entrapment;
- SEPs in conscious persons with severe spinal cord or head injuries (the standard neurologic examination is the most direct way to evaluate any deficits);
- SEPs in diagnosis of cervical spondylytic myeloradiculopathy;
- SEPs in the diagnosis of thoracic outlet syndrome;
- SEPs in the diagnosis or management of acquired metabolic disorders (e.g., lead toxicity, B12 deficiency);
- SEPs in the diagnosis or management of amyotrophic lateral sclerosis (ALS);
- SEPs for pectus excavatum surgery;
- SEPs for prostate surgery;
- Short-latency SSEP study for evaluation of movement disorders;
- Stimulus evoked response during radical prostatectomy;
- VEPs for detecting amnestic mild cognitive impairment;
- VEPs for evaluation and monitoring of birdshot chorioretinopathy;
- VEPs for syringomyelia, syringobulbia, and evaluation of vigabatrin (Sabril)-associated retinal toxicity, screening Plaquenil (hydroxychloroquine) toxicity, as prognostic tests in neonates with perinatal asphyxia and hypoxic-ischemic encephalopathy;
- Vestibular evoked myogenic potentials (VEMP) (e.g., for diagnosis of Meniere's disease or delayed endolymphatic hydrops; differentiation of Meniere disease from vestibular migraine);
- Visual evoked potential for evaluation of neuromyelitis optica spectrum disorder.
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Related Policies
Background
Evoked potentials measure conduction velocities of sensory pathways in the central nervous system using computerized averaging techniques. Three types of evoked potentials are routinely performed:
- somatosensory;
- visual; and
- brainstem auditory.
In each of these tests a peripheral sense organ is electrically stimulated and conduction velocities are recorded for central somatosensory pathways located in the posterior columns of the spinal cord, brain stem, and thalamus, and the primary sensory cortex located in the parietal lobes.
Somatosensory evoked potentials (SEPs or SSEPs) (also known as cerebral sensory evoked potentials) augment the sensory examination and are most useful in assessing the spinal nerve roots, spinal cord, or brain stem for evidence of delayed nerve conduction. Dermatomal somatosensory evoked potentials (DSEPs) are elicited by stimulating the skin "signature" areas of specific nerve roots. Both techniques involve production and recording of small electrophysiological responses of the central nervous system that follow sequential electrical stimulation of peripheral nerves. These small electrophysiological responses are extracted from the background noise of electroencephalography (EEG), usually by signal averaging techniques. Delays in signal propagation suggest lesions of the central sensory pathways. Although controversial, evoked potentials have been used to assess the prognosis of children with spinal cord lesions, brain malformations, and neurodegenerative diseases, as well as young children who are at risk for brain injury, such as preterm infants. Somatosensory evoked potentials measurements have been used to predict outcome in spinal cord injury; however, signal changes on MRI actually may be more useful in determining the severity of injury. Hemorrhage within the spinal cord is readily identified on MRI, and such hemorrhage is predictive of injury severity. Intra-operative SSEP measurements are useful in complex neurologic, orthopedic, and vascular surgical procedures as a means of gauging nerve injury during surgery (e.g., resection of cord tumors).
Somatosensory evoked potentials are altered by conditions that affect the somatosensory pathways, including both focal lesions (such as strokes, tumors, cervical spondylosis, syringomyelia) and diffuse diseases (such as hereditary systemic neurologic degeneration, subacute combined degeneration, and vitamin E deficiencies).
Somatosensory evoked potentials may detect clinically silent brain lesions in multiple sclerosis suspects. Although SEP abnormalities alone are insufficient to establish the diagnosis of multiple sclerosis, the diagnosis can be established when there is also other objective findings (brain plaques on MRI, clinical lesions by history and physical examination, and/or positive CSF (determined by oligoclonal bands detected by established methods (isoelectric focusing) different from any such bands in serum, or by an increased IgG index)).
Fifty to 60 % of multiple sclerosis patients have other concurrent demyelinating lesions that may not be clinically evident, and SSEP may be helpful in documenting these abnormalities. Somatosensory evoked potentials abnormalities are also produced by other diseases affecting myelin (adrenoleukodystrophy and adrenomyelo-neuropathy, metachromatic leukodystrophy, Pelizaeus-Merzbacher disease). In adrenoleukodystrophy and adrenomyeloneuropathy, SSEP abnormalities may be present in asymptomatic heterozygotes. Abnormally large amplitude SEPs, reflecting enhanced cortical excitability, are seen in progressive myoclonus epilepsy, in some patients with photosensitive epilepsy, and in late infantile ceroid lipofuscinosis.
Studies have demonstrated a statistically significant association between abnormal visual evoked potentials (VEPs) and an increased risk of developing clinically definite multiple sclerosis (CDMS). In these studies, patients with suspected MS were 2.5 to 9 times as likely to develop CDMS as patients with normal VEPs. Visual evoked potentials sensitivities ranged from 25 % to 83 %. Visual evoked potentials improved the ability to predict which MS suspects will develop CDMS by as much as 29 %.
Measurement of visual evoked responses (VERs) is the primary means of objectively testing vision in infants and young children suspected of having disorders of the visual system, where the child is too young to report differences in color vision or to undergo assessment of visual fields and visual acuity. A flashing stroboscope or an alternating checkerboard pattern is presented and the wave patterns are recorded. In an infant, vision may be reliably tested using a flashing light during quiet sleep. Lesions affecting the visual pathways can be localized by noting the presence of decreased amplitudes or increased latencies of VERs, and by determining whether VER abnormalities involve one or both eyes. Visual evoked responses are also useful for testing vision in other persons who are not able to communicate.
Brain stem auditory evoked responses (BAERs) are electrical potentials that are produced in response to an auditory stimulus and are recorded from disk electrodes attached to the scalp. Depending on the amount of time elapsed between the "click" stimulus and the auditory evoked response, potentials are classified as early (0 to 10 msec), middle (11 to 50 msec), or late (51 to 500 msec). The early potentials reflect electrical activity at the cochlea, 8th cranial nerve, and brain stem levels; the latter potentials reflect cortical activity. In order to separate evoked potentials from background noise, a computer averages the auditory evoked responses to 1,000 to 2,000 clicks. Early evoked responses may be analyzed to estimate the magnitude of hearing loss and to differentiate among cochlea, 8th nerve, and brainstem lesions.
The clinical utility of BAER over standard auditory testing is due to several of BAER's characteristics:- BAER's resistance to alteration by systemic metabolic abnormalities, medications or pronounced changes in the state of consciousness of the patient; and
- the close association of BAER waveform abnormalities to underlying structural pathology.
Brain stem auditory evoked responses have been proven effective for differentiating conductive from sensory hearing loss, for detecting tumors and other disease states affecting central auditory pathways (e.g., acoustic neuromas), and for noninvasively detecting hearing loss in patients who can not cooperate with subjective auditory testing (e.g., infants, comatose patients). BAER is the test of choice to assess hearing in infants and young children. It is most useful for following asphyxia, hyperbilirubinemia, intracranial hemorrhage, or meningoencephalitis or for assessing an infant who has trisomy. BAER also is useful in the assessment of multiple sclerosis or other demyelinating conditions, coma, or hysteria. Audiometric analysis using multiple sound frequencies is usually preferred over BAER for testing hearing in cooperative patients who are able to report when sounds are heard. Evidence is insufficient at this time to recommend BAER as a useful test to identify patients at increased risk for developing CDMS.
Studies of cognitive evoked potentials (also known as the P300 or P3 cognitive evoked potentials) have been used in research settings to correlate changes in cognitive evoked potentials with clinical changes in cognitive function in patients with dementia (e.g., Alzheimer's disease and Parkinson's disease) and identify the etiology of depression in patients with chronic demyelinating disease. However, there is insufficient evidence regarding the effectiveness of cognitive evoked potential studies in diagnosing or rendering treatment decisions that would affect health outcomes. Furthermore, there is a lack of studies comparing cognitive evoked potential studies with standard neuropsychiatric and psychometric tests used in diagnosing cognitive dysfunction.
The American Academy of Pediatrics (AAP) Task Force on Newborn and Infant Hearing and the Joint Committee on Infant Hearing (JCIH) endorse the implementation of universal newborn hearing screening. Screening should be conducted before discharge from the hospital whenever possible. Physicians should provide recommended hearing screening, not only during early infancy but also through early childhood for those children at risk for hearing loss (e.g., history of trauma, meningitis) and for those demonstrating clinical signs of possible hearing loss.
Prior to July 2008, the U.S. Preventive Services Task Force (USPSTF) recommended screening for hearing loss in all newborn infants, stating that all infants should be screened before 1 month of age. Those infants who do not pass the newborn screening should undergo audiologic and medical evaluation before 3 months of age for confirmatory testing. Because of the elevated risk of hearing loss in infants with risk indicators (e.g., neonatal intensive care unit admission for 2 or more days; syndromes associated with hearing loss, such as Usher syndrome and Waardenburg syndrome; family history of hereditary childhood hearing loss; craniofacial abnormalities; and congenital infections such as cytomegalovirus, toxoplasmosis, bacterial meningitis, syphilis, herpes, and rubella), an expert panel recommends that these children undergo periodic monitoring for 3 years. The USPSTF found good evidence that newborn hearing screening leads to earlier identification and treatment of infants with hearing loss and improves language outcomes. However, additional studies detailing the correlation between childhood language scores and functional outcomes (e.g., school attainment and social functioning) are needed. In July 2008, the USPSTF inactivated its recommendation on "Hearing loss in newborns: Screening". The USPSTF has decided not to review the evidence and update its recommendations, and that the previous evidence review and recommendaton may contain information that is outdated.
"Universal screening for hearing loss is preferred because targeted selective screening for only at-risk infants would fail to identify 50 to 75 percent of all cases of moderate to profound bilateral hearing loss. As a result, hearing loss in a substantial number of hearing-impaired neonates would be delayed with only selective screening. All states in the United States have implemented universal newborn hearing screening (UNHS) programs and most states have laws mandating UNHS. Clinicians should be familiar with their state laws" (Vohr, 2018).
Two types of UNHS tests are commonly used to screen for congenital hearing loss:
- otoacoustic emissions (OAEs) and
- auditory brainstem response (ABR) (Helfand et al, 2001).
Otoacoustic emissions testing evaluates the integrity of the inner ear (cochlea). In response to noise, vibrations of the hair cells in a healthy inner ear generate electrical responses, known as otoacoustic emissions. The absence of OAEs indicates that the inner ear is not responding appropriately to sound. Transient evoked otoacoustic emissions (TEOAEs) are generated in response to wide-band clicks, while distortion product otoacoustic emissions (DPOAE) are a response to tones. Both stimuli are presented via a light-weight ear canal probe. A microphone picks up the signal, and multiple responses are averaged to get a specific repeatable waveform. Otoacoustic emissions are used in screening and diagnosis of hearing impairments in infants, and in young children and patients with cognitive impairments (e.g., mental retardation, dementia) who are unable to respond reliably to standard hearing tests. Otoacoustic emissions are also useful for evaluating patients with tinnitus, suspected malingering, and for monitoring cochlear damage from ototoxic drugs.
The ABR is an electrophysiological response generated in the brainstem in response to auditory signals and composed of either clicks or tones. The stimulus is delivered via earphones or an inserted ear probe, and scalp electrodes pick up the signal. Auditory brainstem response evaluates the integrity of the peripheral auditory system and the auditory nerve pathways up to the brainstem and is able to identify infants with normal cochlear function but abnormal 8th-nerve function (auditory neuropathy). For purposes of neonatal screening, a limited ABR is performed in the nursery using a significantly low intensity level (35 to 40 dB) to rule out marked hearing loss (Schwartz and Schwartz, 1990; Scott and Bhattacharyya, 2002). If testing at this level fails to elicit a response, the infant is referred to an audiologic laboratory for a comprehensive ABR, involving testing at many different intensity levels.
Typically, screening programs use a 2-stage screening approach (either OAE repeated twice, OAE followed by ABR, or ABR repeated twice). Criteria for defining a "pass" or "fail" on the initial screening test vary widely. Comprehensive (diagnostic) OAEs or ABRs are used to diagnose hearing impairments identified by limited (screening) tests.
Auditory brainstem response and OAE have limitations that affect their accuracy in certain patients. Both require a sleeping or quiet child. Middle-ear effusion or debris in the external canal can compromise the accuracy of these tests. Otoacoustic emissions and ABR test the peripheral auditory system and 8th nerve pathway to the brainstem, respectively. They are not designed to identify infants with central hearing deficits. Therefore, infants with risk factors for central hearing deficits, particularly those who have congenital Cytomegalovirus infection or prolonged severe hypoxia at birth, may pass their newborn hearing screens with either OAE or ABR, but develop profound hearing loss in early infancy.
The newer generation of automated screeners are easy to use and do not require highly trained staff. However, equipping hospitals with equipment and sufficient staff can be costly, the staff must be trained to understand the limitations of the techniques, and ongoing quality control is essential to achieve accurate, consistent test results. The importance of technique is illustrated by the results of multicenter studies of universal screening, in which the rates of false positive and technically inadequate examinations varied 10-fold among sites.
There are differences between the guidelines with respect to the screening technology that is endorsed. The Joint Committee on Infant Hearing recommends that all infants have access to screening using a physiologic measure (either otoacoustic emissions [TEOAE or DPOAE] and/or ABR). The AAPstates that although additional research is necessary to determine which screening test is ideal, EOAE and/or ABR are presently the screening methods of choice. The AAP defers recommending a preferred screening test. The USPSTF recommends a 1- or 2-step validated protocol, stating that OAEs followed by ABR in those who failed the first test is a frequently used protocol. Well-maintained equipment, thoroughly trained staff, and quality control programs are also recommended to avoid false-positive tests.
The American Academy of Audiology on "Childhood hearing screening guidelines" (2011) recommends OAE use only for preschool and school age children for whom pure tone screening is not developmentally appropriate (ability levels less than 3 years of age).
UpToDate review on "Screening the newborn for hearing loss" (Vohr, 2018) states that with the adoption of universal newborn hearing screening (UNHS), the age at identification of hearing loss has decreased from a range of 24 to 30 months to 2 to 3 months of age. For infants who passed the initial hearing screen, follow-up consists of continued routine monitoring of language acquisition, auditory skills, middle ear status, and attention to parental concerns. "Additional oversight and testing are reserved for term infants who failed OAE but passed AABR, NICU graduates, and infants with risk factors for hearing loss who passed newborn screen".
It is recommended that infants who fail the initial hearing screen have additional audiologic evaluation by three months of age (Vohr, 2018).
Cortical auditory evoked responses (CAERs) measure the later-occurring auditory evoked potentials reflecting cortical activity in response to an auditory stimulus (UBC, 2005). Cortical auditory evoked responses have a long latency, compared to the short latency auditory evoked responses; they have been used in clinical research to evaluate the timing, sequence, strength, and anatomic location of brain processes involved with the perception of sounds. Current research underway concerns the use of CAERs to understand the brain processes underlying basic hearing percepts such as loudness, pitch, and localisation, as well as those processes involved with speech perception (UBC, 2005).
Vestibular evoked myogenic potentials (VEMP), also known as click evoked neurogenic vestibular potentials, are presumed to originate in the saccule. They are recorded from surface electrodes over the sternocleidomastoid muscles, and can be activated by means of brief, high-intensity acoustic stimuli. Papathanasiou et al (2003) stated that VEMP testing is a possible new diagnostic technique that may be specific for the vestibular pathway. It has potential use in patients with symptoms of dizziness, sub-clinical symptoms in multiple sclerosis, and in disorders specific for the vestibular nerve. There is a lack of reliable evidence from well controlled, prospective studies demonstrating that VEMP testing alters management such that clinical outcomes are improved. Current evidence-based guidelines on the management of neurological disorders from leading medical professional organizations have not incorporated VEMP testing in diagnostic and treatment algorithms. The American Academy of Neurology considered VEMP as an investigational technique (Fife et al, 2000). Guidelines prepared for the State of Colorado (DLE, 2006) state that VEMP "is currently a research tool and is not recommended for routine clinical use." In a review of the literature, Rauch (2006) states that VEMP holds great promise for diagnosing and monitoring Ménière's disease and some other neurotologic disorders. Rauch notes, however, that the methods, equipment, and applications for vestibular evoked myogenic potential testing are not yet standardized, and many aspects of vestibular evoked myogenic potential and its use have not yet been adequately studied or described.
Brantberg et al (2007) studied VEMP in response to sound stimulation (500 Hz tone burst, 129 dB SPL) in 1,000 consecutive patients. Vestibular evoked myogenic potentials from the ear with the larger amplitude were evaluated based on the assumption that the majority of the tested patients probably had normal vestibular function in that ear. Patients with known bilateral conductive hearing loss, with known bilateral vestibular disease and those with Tullio phenomenon were not included in the evaluation. It was found that there was an age-related decrease in VEMP amplitude and an increase in VEMP latency that appeared to be rather constant throughout the whole age span. Vestibular evoked myogenic potentials data were also compared to an additional group of 10 patients with Tullio phenomenon. Although these 10 patients did have rather large VEMP, equally large VEMP amplitudes were observed in a proportion of unaffected subjects of a similar age group. Thus, the findings of a large VEMP amplitude in response to a high-intensity sound stimulation is not, per se, distinctive for a significant vestibular hypersensitivity to sounds.
Muyts et al (2007) provided an overview of vestibular function testing and highlights the new techniques that have emerged during the past 5 years. Since the introduction of video-oculography as an alternative to electro-oculography for the assessment of vestibular-induced eye movements, the investigation of the utricle has become a part of vestibular function testing, using unilateral centrifugation. Vestibular evoked myogenic potentials have become an important test for assessing saccular function, although further standardization and methodological issues remain to be clarified. Galvanic stimulation of the labyrinth also is an evolving test that may become useful diagnostically. The authors concluded that a basic vestibular function testing battery that includes ocular motor tests, caloric testing, positional testing, and earth-vertical axis rotational testing focuses on the horizontal semicircular canal. Newer methods to investigate the otolith organs are being developed. These new tests, when combined with standard testing, will provide a more comprehensive assessment of the complex vestibular organ.
Magnetic stimulation of the brain and spine elicits so-called motor evoked potentials (MEPs) (Goetz, 2005). The latency of the motor responses can be measured, and central conduction time can be estimated by comparing the latency of the responses elicited by cerebral and spinal stimulation. Abnormalities have been described in patients with a variety of central disorders including multiple sclerosis, amyotrophic lateral sclerosis, stroke, and certain degenerative disorders. An assessment by the McGill University Health Centre on use of intraoperative neurophysiological monitoring during spinal surgery stated that there is sufficient evidence to support the conclusion that intraoperative spinal monitoring using SSEPs and MEPs during surgical procedures that involve risk of spinal cord injury is an effective procedure that is capable of substantially diminishing this risk (Erickson et al, 2005). The report explained that intra-operative spinal cord injury during spinal surgery generally compromises both motor and somatosensory pathways; therefore the use of both of these independent techniques in parallel has been proposed and is seen as a safeguard should one of the monitoring techniques fail. Combination of SSEP monitoring with MEP monitoring is also proposed to reduce false-positive results, and eliminate the need for the wake-up test. The assessment identified 11 studies, all case series, of the combined use of SSEPs and MEPs in neurophysiological monitoring during spinal surgery. The assessment found that, in several reports, combined SSEP and MEP monitoring was shown to have greater sensitivity than SSEP alone. The report also noted that the addition of MEP monitoring where SSEP monitoring is already being performed is considered to be relatively straightforward, adding little to the overall effort and resources employed in intraoperative neurophysiological monitoring.
A study by Schwarz et al (2007) illustrated the advantage of intraoperative monitoring of spinal cord motor tracts directly by recording motor evoked potentials in addition to somatosensory evoked potentials. Investigators reviewed the intraoperative neurophysiological monitoring records of 1121 consecutive patients (834 female and 287 male) with adolescent idiopathic scoliosis (mean age, 13.9 years) treated between 2000 and 2004 at four pediatric spine centers. The same group of experienced surgical neurophysiologists monitored spinal cord function in all patients with use of a standardized multimodality technique with the patient under total intravenous anesthesia. A relevant neurophysiological change (an alert) was defined as a reduction in amplitude (unilateral or bilateral) of at least 50% for somatosensory evoked potentials and at least 65% for transcranial electric motor evoked potentials compared with baseline. The investigators reported that 38 (3.4%) of the 1121 patients had recordings that met the criteria for a relevant signal change (i.e., an alert). Of those 38 patients, 17 showed suppression of the amplitude of motor evoked potentials in excess of 65% without any evidence of changes in somatosensory evoked potentials. In nine of the 38 patients, the signal change was related to hypotension and was corrected with augmentation of the blood pressure. The remaining 29 patients had an alert that was related directly to a surgical maneuver. Three alerts occurred following segmental vessel clamping, and the remaining 26 were related to posterior instrumentation and correction. Nine (35%) of these 26 with an instrumentation-related alert, or 0.8% of the cohort, awoke with a transient motor and/or sensory deficit. Seven of these nine patients presented solely with a motor deficit, which was detected by intraoperative monitoring of motor evoked potentials in all cases, and two patients had only sensory symptoms. The investigators reported that somatosensory evoked potential monitoring failed to identify a motor deficit in four of the seven patients with a confirmed motor deficit. Furthermore, when changes in somatosensory evoked potentials occurred, they lagged behind the changes in transcranial electric motor evoked potentials by an average of approximately five minutes. With an appropriate response to the alert, the motor or sensory deficit resolved in all nine patients within one to 90 days.
A systematic evidence review of multimodality intraoperative monitoring (MIOM), including somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) recording, during spinal cord/spinal column surgery, reached the following conclusions (Hadley, et al., 2017): "Robust class I medical evidence supports the use of electrophysiological monitoring including SSEP and MEP recordings during spinal cord/spinal column surgery as a diagnostic adjunct to assess spinal cord integrity in the perioperative setting. IOM, applied in this way, is a valid and sensitive means to detect neurological injury during spinal cord and spinal column surgical procedures.
The systematic review concluded (Hadley, et al., 2017): "The use of IOM as a therapeutic tool during spinal surgery, however, has not been shown to be successful in reducing the rate of perioperative neurological deterioration or to improve neurological outcome during spinal surgery procedures. To date, there is no meaningful medical evidence (ie, class I or II) to support a therapeutic relationship between the use of IOM in spinal cord/spinal column surgery and neurological outcome. Two class II medical evidence studies on this issue are negative/refute the utility of IOM as a therapeutic adjunct in surgery within and around the spinal cord. For this reason, the use of IOM during spinal cord or spinal column surgery cannot be considered a “standard of care.”
The clinical utility of MEPs outside of the operative setting, however, is unclear and at the present time the magnetic stimulation of central structures is regarded as investigational (Goetz, 2003; Miller, 2005).
In a prospective consecutive case series study, Lee et al (2009) evaluated the side effects of microvascular decompression (MVD) on hearing and described the main intra-operative ABR changes. The study included 22 patients who underwent MVD with monitoring of ABRs. The latency prolongation and wave loss were analyzed at each surgical step, which were decided arbitrarily. Patients were divided into 4 groups depending on degree of change of wave V. Group 1 consisted of minimal change, whereas group 4 was permanent loss of wave V. Hearing changes were evaluated in 20 patients in the 4 groups who were available for post-operative hearing results. Loss of wave I, III, and V occurred with 6 %, 13 %, and 9 % of surgical actions, respectively. Wave III disappearance was identified as the earliest and most sensitive sign and was usually preceded by the disappearance of wave V. The greatest prolongation of wave V at more than 1.0 ms developed statistically significant sensorineural hearing loss in the range of 10 dB. One patient in group 4 experienced deafness. The authors concluded that in addition to the significant delay of wave V, useful recognition of early changes of wave III is possible and enables a change of microsurgical maneuvers to favor ABR recovery.
Polo and Fischer (2009) stated that BAEP monitoring is a useful tool to decrease the danger of hearing loss during pontocerebellar angle surgery, particularly in MVD. Critical complications arising during MVD surgery are the stretching of the VIII nerve – the main cause of hearing loss – labyrinthine artery manipulation, direct trauma with instruments, or a nearby coagulation, and at end of the surgery neocompression of the cochlear nerve by the prosthesis positioned between the conflicting vessel(s) and the VIIth-VIIIth nerve complex. All these dangers warrant the use of BAEP monitoring during the surgical team's training period. Based on delay in latency of peak V, these investigators established warning thresholds that can provide useful feedback to the surgeon to modify the surgical strategy: the initial signal at 0.4 ms is considered the safety limit. A second signal threshold at 0.6 ms (warning signal for risk) corresponds to the group of patients without resultant hearing loss. The third threshold characterized by the delay of peak V is at 1 ms (warning signal for a potentially critical situation). BAEP monitoring provides the surgeon with information on the functional state of the auditory pathways and should help avoid or correct maneuvers that can harm hearing function. BAEP monitoring during VIIth-VIIIth complex surgery, particularly in MVD of facial nerves for hemifacial spasm (HFS) is very useful during the learning period.
Huang and colleagues (2009) determined the reliability of
- intra-operative monitoring by stimulated electromyography (EMG) of the facial nerve to predict the completeness of MVD for HFS, and
- BAEP to predict post-operative hearing disturbance.
These investigators conducted a prospective study of 36 patients who received MVD for HFS. They confirmed the disappearance of an abnormal muscle response in the facial nerve EMG to predict the completeness of MVD, and performed BAEP monitoring to predict post-operative hearing disturbance. The sensitivity, specificity and accuracy of facial nerve EMG and BAEP monitoring were evaluated. The sensitivity, specificity and accuracy of facial nerve EMG were 0.97, 1.0 and 0.97, respectively, and that for BAEP monitoring were 1.0, 0.94 and 0.94, respectively. There was 1 false-positive result for facial nerve EMG, and 2 false-positive results for BAEP monitoring. No false-negative result was encountered for either EMG or BAEP monitoring. Facial nerve EMG correctly predicted whether MVD was successful in 35 out of 36 patients, and BAEP correctly predicted whether there was post-operative hearing disturbance in 34 out of 36 patients. The authors concluded that intra-operative facial nerve EMG provides a real-time indicator of successful MVD during an operation while BAEP monitoring may provide an early warning of hearing disturbance after MVD.
In a systematic review, van Laerhoven et al (2013) examined the prognostic value of currently used clinical tests in neonatal patients with perinatal asphyxia and hypoxic-ischemic encephalopathy (HIE). Searches were made on MedLine, Embase, Central, and CINAHL for studies occurring between January 1980 and November 2011. Studies were included if they- evaluated outcome in term infants with perinatal asphyxia and HIE,
- evaluated prognostic tests, and
- reported outcome at a minimal follow-up age of 18 months.
Study selection, assessment of methodological quality, and data extraction were performed by 3 independent reviewers. Pooled sensitivities and specificities of investigated tests were calculated when possible. Of the 259 relevant studies, 29 were included describing 13 prognostic tests conducted 1,631 times in 1,306 term neonates. A considerable heterogeneity was noted in test performance, cut-off values, and outcome measures. The most promising tests were amplitude-integrated electroencephalography (sensitivity 0.93, [95 % CI: 0.78 to 0.98]; specificity 0.90 [0.60 to 0.98]), EEG (sensitivity 0.92 [0.66 to 0.99]; specificity 0.83 [0.64 to 0.93]), and VEPs (sensitivity 0.90 [0.74 to 0.97]; specificity 0.92 [0.68 to 0.98]). In imaging, diffusion weighted MRI performed best on specificity (0.89 [0.62 to 0.98]) and T1/T2-weighted MRI performed best on sensitivity (0.98 [0.80 to 1.00]). Magnetic resonance spectroscopy demonstrated a sensitivity of 0.75 (0.26 to 0.96) with poor specificity (0.58 [0.23 to 0.87]). The authors concluded that this evidence suggested an important role for amplitude-integrated electroencephalography, EEG, VEPs, and diffusion weighted and conventional MRI. Moreover, they stated that given the heterogeneity in the tests' performance and outcomes studied, well-designed, large prospective studies are needed.
Balzer et al (1998) reported on the results of a descriptive case series of the use of somatosensory evoked potentials during lumbrosacral spine surgery. SSEPs and EMG activity were simultaneously recorded for 44 patients who underwent surgical procedures to decompress and stabilize the lumbosacral spine, using pedicle screw instrumentation. Indications included degenerative spondylolisthesis (22), pars fracture with spondylolisthesis (9), failed back syndrome (7), burst/compression fracture (4), and instability from metastasis (2). The specific level of the lumbar spine for each procedure included in this series was not reported. All neurosurgical procedures were performed by a single surgeon. The authors reported that, in two cases, changes in SSEPs and spontaneous EMG activity were noted and were correlated with postoperative patient complaints.
Rothstein (2009) stated that the early recognition of comatose patients with a hopeless prognosis – regardless of how aggressively they are managed – is of utmost importance. Median SSEP supplement and enhance neurological examination findings in anoxic-ischemic coma and are useful as an early guide in predicting outcome. The key finding is that bilateral absence of cortical evoked potentials reliably predicts unfavorable outcome in comatose patients after cardiac arrest. The author studied 50 comatose patients with preserved brainstem function after cardiac arrest. All 23 patients with bilateral absence of cortical evoked potentials died without awakening. Neuropathological study in 7 patients disclosed widespread ischemic changes or frank cortical laminar necrosis. The remaining 27 patients with normal or delayed central conduction times had an uncertain prognosis because some died without awakening or entered a persistent vegetative state. The majority of patients with normal central conduction times had a good outcome, whereas a delay in central conduction times increased the likelihood of neurological deficit or death. Greater use of SSEP in anoxic-ischemic coma would identify those patients unlikely to recover and would avoid costly medical care that is to no avail.
An UpToDate review on "Hypoxic-ischemic brain injury: Evaluation and prognosis" (Weinhouse and Young, 2012) states that several ancillary tests have been studied in the period after anoxic injury; these are often helpful at arriving at an earlier prognostic determination than would be possible with clinical testing alone. Somatosensory evoked potentials are the averaged electrical responses in the central nervous system to somatosensory stimulation. Bilateral absence of the N20 component of the SSEP with median nerve stimulation at the wrist in the 1st week (usually between 24 and 72 hours) from the arrest has a pooled likelihood ratio of 12.0 (95 % confidence interval [CI]: 5.3 to 26.6) and a false-positive rate of zero % for an outcome no better than persistent vegetative state. Repeated testing should be considered when the N20 responses are present in the first 2 to 3 days from the cardiac arrest, as they may later disappear. The clinical operating characteristics of other evoked potentials (brainstem, auditory, visual, middle latency, and event-related) have not been adequately evaluated. Somatosensory evoked potentials are the best validated and most reliable of the ancillary tests currently available for clinical use.
The Quality Standards Subcommittee of the American Academy of Neurology's Practice Parameter on "Prediction of outcome in comatose survivors after cardiopulmonary resuscitation (an evidence-based review)" (Wijdicks et al, 2006) recommended the assessment of poor prognosis can be guided by the bilateral absence of cortical SSEPs (N20 response) within 1 to 3 days (recommendation level B).
Raggi et al (2010) noted that amyotrophic lateral sclerosis (ALS) is increasingly recognized to be a multi-system disease, involving associative areas in addition to the motor cortex and therefore affecting cognition. Patients with ALS may present with subtle behavioral and executive dysfunctions or, less frequently, with a manifest fronto-temporal dementia. Event-related potentials (ERPs) are a high-temporal resolution technique, which can be used to explore the presence of cognitive dysfunction. All the primary studies reviewed here have shown ERP abnormalities in groups of non-demented patients affected by sporadic ALS compared to healthy controls. The ERP results support findings of neuropsychological and imaging studies. The authors concluded that prospective studies combining simultaneous neuropsychological and imaging investigations are needed to assess the possible role of ERPs in the early detection and follow-up of cognitive dysfunction in ALS patients.
The U.S. Preventive Services Task Force (USPSTF) has not recommended vision screening of infants and young children. The 2011 USPSTF recommendation does not support vision screening for children less than 3 years of age, as it concludes that the current evidence is insufficient to assess the balance of benefits and harms to this subpopulation. This position is consistent with the current recommendations of the American Academy of Ophthalmology and the American Association for Pediatric Ophthalmology and Strabismus and other professional organizations.
In a review on "Facial nerve monitoring during cerebellopontine angle and skull base tumor surgery", Acioly et al (2013) stated that intraoperative neuromonitoring has been established as one of the methods by which modern neurosurgery can improve surgical results while reducing morbidity. Despite routine use of intraoperative facial nerve (FN) monitoring, FN injury still is a complication of major concern due to severe negative impact on patient's quality of life. Through searches of PubMed, these investigators provided a systematic review of the current literature up to February, 2011, emphasizing all respects of FN monitoring for cerebellopontine angle and skull base tumor surgery from description to current success on function prediction of standard and emerging monitoring techniques. Currently, standard monitoring techniques comprise direct electrical stimulation (DES), free-running electromyography (EMG), and facial motor evoked potential (FMEP). These researchers included 62 studies on function prediction by investigating DES (43 studies), free-running EMG (13 studies), and FMEP (6 studies) criteria. DES mostly evaluated post-operative function by using absolute amplitude, stimulation threshold, and proximal-to-distal amplitude ratio, whereas free-running EMG used the train-time criterion. The prognostic significance of FMEP was assessed with the final-to-baseline amplitude ratio, as well as the event-to-baseline amplitude ratio and waveform complexity. The authors concluded that although there is a general agreement on the satisfactory functional prediction of different electrophysiological criteria, the lack of standardization in electrode montage and stimulation parameters precludes a definite conclusion regarding the best method. Moreover, studies emphasizing comparison between criteria or even multi-modal monitoring and its impact on FN anatomical and functional preservation are still lacking in the literature.
Mauguiere et al (1997) examined if abnormalities of central conduction could be detected prospectively in patients with epilepsy treated with vigabatrin (VGB) as long-term add-on medication. A total of 201 patients with refractory partial epilepsy were enrolled and monitored for as long as 2 years. Vigabatrin was added to the treatment at an average dose of 2 to 3g/day. Conduction in somatosensory and visual pathways was assessed by median nerve SEP and pattern VEP recordings performed at inclusion and once every 6 months. The upper limit and test-retest variability of EP latencies were evaluated at time of enrollment in the patient group. Prolonged N13-N20 or P14-N20 SEP intervals and P100 VEP latency greater than 2.5 SD above the baseline mean, observed on repeated runs in the same session and exceeding the test-retest variability at enrollment were considered to indicate central conduction slowing. A total of 109 patients completed the 2-year study period, and 92 discontinued VGB, of whom 37 were monitored with regard to EP until the end of the study. No consistent change in SEP or VEP was observed in the entire group during VGB treatment. The number of occasional EP values outside the baseline range in patients treated with VGB similar to that in patients whose VGB treatment had been discontinued. The authors concluded that they detected no evidence of changes in SEP and VEP attributable to altered neuronal conduction in the CNS during long-term VGB treatment.
Zgorzalewicz and Galas-Zgorzalewicz (2000) estimated the effects of VGB as add-on therapy on VEP and BAEP. The investigation covered 100 epileptic patients from 8 to 18 years of age. The treatment included therapy with carbamazepine (CBZ) or valproate acid (VPA) using slow release formulations of these anti-epileptic drugs (AEDs). Combination therapy was administered using add-on VGB in the recommended dose 57.4 +/- 26.5 mg/kg body weight/day. VEP and BAEP were recorded by means of Multiliner (Toennies, Germany). The obtained values were compared with age-matched control group. Compared to control groups, significant differences in epileptic groups emerged in latencies of the peak III, V along with the inter-peak intervals I-III of BAEP. Also VEP studies showed the reduction of N75/P100 and P100/N145 amplitudes. The authors concluded that adding VGB did not significantly increase the percentage of pathological abnormalities observed from EPs.
In a prospective cohort study, Zuniga et al (2012) characterized both cervical and ocular vestibular-evoked myogenic potential (cVEMP, oVEMP) responses to air-conducted sound (ACS) and midline taps in Meniere disease (MD), vestibular migraine (VM), and controls, and determined if cVEMP or oVEMP responses can differentiate MD from VM. Unilateral definite MD patients (n = 20), VM patients (n = 21) by modified Neuhauser criteria, and age-matched controls (n = 28) were included in this study; cVEMP testing used ACS (clicks), and oVEMP testing used ACS (clicks and 500-Hz tone bursts) and midline tap stimuli (reflex hammer and Mini-Shaker). Outcome parameters were cVEMP peak-to-peak amplitudes and oVEMP n10 amplitudes. Relative to controls, MD and VM groups both showed reduced click-evoked cVEMP (p < 0.001) and oVEMP (p < 0.001) amplitudes. Only the MD group showed reduction in tone-evoked amplitudes for oVEMP. Tone-evoked oVEMPs differentiated MD from controls (p = 0.001) and from VM (p = 0.007). The oVEMPs in response to the reflex hammer and Mini-Shaker midline taps showed no differences between groups (p > 0.210). The authors concluded that using these techniques, VM and MD behaved similarly on most of the VEMP test battery. A link in their pathophysiology may be responsible for these responses. The data suggested a difference in 500-Hz tone burst-evoked oVEMP responses between MD and MV as a group. However, no VEMP test that was investigated in segregated individuals with MD from those with VM.
Heravian et al (2011) assessed the usefulness of color vision, photo stress recovery time (PSRT), and VEP in early detection of ocular toxicity of hydroxychloroquine (HCQ), in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). A total of 86 patients were included in the study and divided into 3 groups: with history of HCQ use: interventional 1 (Int.1) without fundoscopic changes and Int.2 with fundoscopic changes; and without history of HCQ use, as control. Visual field, color vision, PSRT and VEP results were recorded for all patients and the effect of age, disease duration, treatment duration and cumulative dose of HCQ on each test was assessed in each group. There was a significant relationship among PSRT and age, treatment duration, cumulative dose of HCQ and disease duration (p < 0.001 for all). Color vision was normal in all the cases. P100 amplitude was not different between the 3 groups (p = 0.846), but P100 latency was significantly different (p = 0.025) and for Int.2 it was greater than the others. The percentage of abnormal visual fields for Int.2 was more than Int.1 and control groups (p = 0.002 and p = 0.005, respectively), but Int.1 and control groups were not significantly different (p > 0.50). In the early stages of maculopathy, P100 latencies of VEP and PSRT are useful predictors of HCQ ocular toxicity. In patients without ocular symptoms and fundoscopic changes, the P100 latency of VEP predicts more precisely than the others.
Current guidelines from the American Academy of Ophthalmology do not recommend visual evoked potentials for screening or diagnosis of hydroxychloroquine toxicity (Marmor, et al., 2011; Karmel, 2011; Scechtman and Karpecki, 2011). Shechtman and Karpecki (2011) noted that the 2011 testing guidelines for patients on Plaquenil listed
- dilated fundus examination,
- automated 10-2 VF,
- spectral domain optical coherence tomography (SD-OCT), fundus autofluorescence (FAF) or multi-focal electroretinography (mfERG) (if available), and
- photography as screening tests.
Visual evoked potentials were not mentioned as a screening tool. Furthermore, the screening guidelines on “Hydroxychloroquine toxicity” by Schwartz and Mieler (2011) did not mention the use of VEP. An UpToDate Drug Information on “Hydroxychloroquine” notes that “Ophthalmologic exam at baseline and every 3 months during prolonged therapy (including visual acuity, slit-lamp, fundoscopic, and visual field exam); muscle strength (especially proximal, as a symptom of neuromyopathy) during long-term therapy”. Visual evoked potentials were not mentioned as a screening tool. Also, an UpToDate review on “Antimalarial drugs in the treatment of rheumatic disease” (Wallace, 2013) does not mention the use of VEPs.
- evaluated outcome in term infants with perinatal asphyxia and HIE,
- evaluated prognostic tests, and
- reported outcome at a minimal follow-up age of 18 months.
Study selection, assessment of methodological quality, and data extraction were performed by 3 independent reviewers. Pooled sensitivities and specificities of investigated tests were calculated when possible. Of the 259 relevant studies, 29 were included describing 13 prognostic tests conducted 1,631 times in 1,306 term neonates. A considerable heterogeneity was noted in test performance, cut-off values, and outcome measures. The most promising tests were amplitude-integrated electroencephalography (sensitivity 0.93, [95 % CI: 0.78 to 0.98]; specificity 0.90 [0.60 to 0.98]), EEG (sensitivity 0.92 [0.66 to 0.99]; specificity 0.83 [0.64 to 0.93]), and VEPs (sensitivity 0.90 [0.74 to 0.97]; specificity 0.92 [0.68 to 0.98]). In imaging, diffusion weighted MRI performed best on specificity (0.89 [0.62 to 0.98]) and T1/T2-weighted MRI performed best on sensitivity (0.98 [0.80 to 1.00]). Magnetic resonance spectroscopy demonstrated a sensitivity of 0.75 (0.26 to 0.96) with poor specificity (0.58 [0.23 to 0.87]). The authors concluded that this evidence suggested an important role for amplitude-integrated electroencephalography, EEG, VEPs, and diffusion weighted and conventional MRI. Moreover, they stated that given the heterogeneity in the tests' performance and outcomes studied, well-designed, large prospective studies are needed.
In a retrospective analysis of a case series, Silverstein et al (2014) described a novel technique to monitor femoral nerve function by analyzing the saphenous nerve SSEP during transpsoas surgical exposures of the lumbar spine. Institutional review board approval was granted for this study and the medical records along with the intraoperative monitoring reports from 41 consecutive transpsoas lateral interbody fusion procedures were analyzed. The presence or absence of intraoperative changes to the saphenous nerve SSEP was noted and the post-operative symptoms and physical examination findings were noted. Changes in SSEP were noted in 5 of the 41 surgical procedures, with 3 of the patients waking up with a femoral nerve deficit. None of the patients with stable SSEP's developed sensory or motor deficits post-operatively. No patient in this series demonstrated intraoperative EMG changes indicative of an intraoperative nerve injury. The authors concluded that saphenous nerve SSEP monitoring may be a beneficial tool to detect femoral nerve injury related to transpsoas direct lateral approaches to the lumbar spine. These preliminary findings need to be validated by well-designed studies.
Fix and colleagues (2015) noted that amnesic mild cognitive impairment (MCIa) is often characterized as an early stage of Alzheimer's dementia (AD). The latency of the P2, an electroencephalographic component of the flash VEP (FVEP), is significantly longer in those with AD or MCIa when compared with controls. In a pilot study, these investigators examined the diagnostic accuracy of several FVEP-P2 procedures in distinguishing people with MCIa and controls. The latency of the FVEP-P2 was measured in participants exposed to a single flash condition and 5 double-flash conditions. The double-flash conditions had different inter-stimulus intervals between the pair of strobe flashes. Significant group differences were observed in the single-flash and 2 of the double-flash conditions. One of the double-flash conditions (100 ms) displayed a higher predictive accuracy than the single-flash condition, suggesting that this novel procedure may have more diagnostic potential. Participants with MCIa displayed similar P2 latencies across conditions, while controls exhibited a consistent pattern of P2 latency differences. These differences demonstrated that the double stimulation procedure resulted in a measurable refractory effect for controls but not for those with MCIa. The authors concluded that the pattern of P2 group differences suggested that those with MCIa have compromised cholinergic functioning that resulted in impaired visual processing. They stated that results from the present investigation lend support to the theory that holds MCIa as an intermediate stage between normal healthy aging and the neuropathology present in AD; and measuring the FVEP-P2 during several double stimulation conditions could provide diagnostically useful information about the health of the cholinergic system.
Loudness-Dependence of Auditory Evoked Potentials
In a pilot study, Uhl and colleagues (2012) measured serotonergic activity in a follow-up study of suicidal patients. In particular, these researchers examined if suicide attempts or suicidal states cause changes in the loudness dependence of auditory evoked potentials (LDAEP). A total of 13 patients (6 males; mean age of 40.9 ± 11.3 years; range of 20 to 61) with a major depressive episode who had attempted suicide or had suicidal plans (Hamilton Depression Rating Scale item 3 [suicidality] greater than or equal to 3) were included in the study; LDAEP and psychometric measurements took place about 2, 5, 9 and 16 days after attempted suicide or suicidal action. On day 9, LDAEP was significantly higher compared to day 2 and day 16; there was a similar tendency compared to day 5. Instability of central serotonergic function was suggested resulting in reduced serotonergic activity about 1 week after suicide attempt. The authors concluded that further studies are needed that include larger samples in order to distinguish between different psychiatric diseases and to consider confounding factors like gender, medication, smoking, impulsivity or lethality of suicidal action.
GraBnickel et al (2015) stated that differences in central serotonergic function due to affective disorders and due to extraordinary situations like suicidality may be visualized using the LDAEP. A total of 20 patients (11 males; mean age of 43.25 ± 10.85, age range of 20 to 61) suffering from a major depressive episode who had either acutely attempted suicide or who had suicidal plans and behavior, which were reflected by item 3 of Hamilton Depression Rating Scale greater than or equal to 3 (suicidality), were included in the study. Furthermore, these researchers compared subjects’ LDAEP to those of non-suicidal depressed patients as well as to healthy volunteers, each matched according to age and gender; LDAEP measurement and psychometric tests took place about 2, 5, 9, 16 and 30 days after acute suicidal action or suicide attempts. In contrast to previous results, significant differences in LDAEP could not have been shown in between the suicidal group, or by comparing results of suicidal patients to non-suicidal depressed patients or to healthy volunteers. However, when the LDAEP of non-suicidal depressed patients were compared to healthy volunteers, there was a trend for a higher LDAEP in the healthy volunteers. The authors concluded that further studies are needed to ascertain further influences on serotonergic function and confounding factors like medication, smoking, age, gender, co-morbidities and methods of suicidal attempt.
Pak et al (2015) noted that the relationship between suicidality and the LDAEP remains controversial. These investigators reviewed the literature related to the LDAEP and suicide in patients with major depressive disorder, and suggested future research directions. Serotonergic dysfunction in suicidality seems to be more complicated than was originally thought. Studies of suicide based on the LDAEP have produced controversial results, but it is possible that these were due to differences in study designs and the smallness of samples. For example, some studies have evaluated suicide ideation and the LDAEP, while others have evaluated suicide attempts and the LDAEP. Furthermore, some of the latter studies enrolled acute suicide attempters, while others enrolled those with the history of previous suicide attempts, irrespective of whether these were acute or chronic. Thus, a more robust study design is needed in future studies (e.g., by evaluating the LDAEP immediately after a suicide attempt rather than in those with a history of suicide attempts and suicide ideation in order to reduce bias). Moreover, the authors stated that genuine suicide attempt, self-injurious behaviors, and faked suicide attempt need to be discriminated in the future.
Intraoperative Motor Evoked Potentials During Descending and Thoraco-Abdominal Aortic Aneurysm Repair
Fok and colleagues (2015) stated that paraplegia remains the most feared and a devastating complication after descending and thoraco-abdominal aneurysm operative repair (DTA and TAAAR). Neuro-monitoring, particularly use of MEPs, for this surgery has gained popularity. However, ambiguity remains regarding its use and benefit. These researchers systematically reviewed the literature to evaluate the benefit and applicability of neuro-monitoring in DTA and TAAAR. Electronic searches were performed on 4 major databases from inception until February 2014 to identify relevant studies. Eligibility decisions, method quality, data extraction, and analysis were performed according to predefined clinical criteria and end-points. Among the studies matching the inclusion criteria, a total of 1,297 patients had MEP monitoring during DTA and TAAAR. In-hospital mortality was low (6.9 % ± 3.6). Immediate neurological deficit was low (3.5 % ± 2.6). In 1/3 of patients (30.4 % ± 14.2), the MEPs dropped below threshold, which were 30.4 % and 29.4 % with threshold levels of 75 % and 50 %, respectively. A range of surgical techniques were applied after reduction in MEPs. Most patients whose MEPs dropped and remained below threshold had immediate permanent neurological deficit (92.0 % ± 23.6). Somatosensory-evoked potentials were reported in 1/3 of papers with little association between loss of SEPs and permanent neurological deficit (16.7 % ± 28.9 %). The authors concluded that they demonstrated that MEPs are useful at predicting paraplegia in patients who lose their MEPs and did not regain them intra-operatively. Moreover, they stated that to date, there is no consensus regarding the applicability and use of MEPs; current evidence does not mandate or support MEP use.
Motor Evoked Potentials for Evaluation of Wilson's Disease
Bembenek et al (2015) stated that Wilson's disease (WD) is a metabolic brain disease resulting from improper copper metabolism. Although pyramidal symptoms are rarely observed, sub-clinical injury is highly possible as copper accumulates in all brain structures. The usefulness of MEPs in pyramidal tracts damage evaluation still appears to be somehow equivocal. These investigators searched for original papers examining the value of transcranial magnetic stimulation (TMS) elicited MEPs with respect to motor function of upper and lower extremity in WD. They searched PubMed for original papers evaluating use of MEPs in WD using key words: "motor evoked potentials Wilson's disease" and "transcranial magnetic stimulation Wilson's disease". These researchers found 6 articles using the above key words. One additional article and 1 case report were found while viewing the references lists; thus, these investigators included 8 studies. Number of patients in studies was low and their clinical characteristic was variable; there were also differences in methodology. Abnormal MEPs were confirmed in 20 to 70 % of study participants; MEPs were not recorded in 7.6 to 66.7 % of patients. Four studies reported significantly increased cortical excitability (up to 70 % of patients). Prolonged central motor conduction time was observed in 4 studies (30 to 100 % of patients); 1 study reported absent or prolonged central motor latency in 66.7 % of patients. The authors concluded that although MEPs may be abnormal in WD, this has not been thoroughly assessed. Moreover, they stated that further studies are needed to evaluate MEPs' usefulness in evaluating pyramidal tract damage in WD.
Somatosensory Evoked Potentials as Prognostic Tests in Neonates with Hypoxic-Ischemic Encephalopathy
Garfinkle and colleagues (2015) noted that SEPs were reported to have high positive-predictive value (PPV) for neuro-developmental impairment (NDI) in neonates with moderate or severe hypoxic-ischemic encephalopathy (HIE). These researchers evaluated if this predictive value remains high with the use of therapeutic hypothermia. A cohort of HIE neonates treated with hypothermia was recruited between September 2008 and September 2010; SEPs were elicited after hypothermia and classified as bilateral absent N19, abnormal N19 (i.e., delayed or unilateral absent), or normal. Qualitative evaluation of MRI was also performed. The primary outcome was moderate or severe NDI around 2 years of age. Somatosensory evoked potentials were performed after hypothermia in 26 of 34 neonates submitted to hypothermia with adequate follow-up at a median day of life 11 (inter-quartile range [IQR]: 9 to 13). Twenty-three (88 %) had moderate encephalopathy; 11 neonates (42 %) had bilateral absent N19, 4 of whom had NDI, while 15 neonates (58 %) had either abnormal or normal N19, of whom only 1 had NDI. Somatosensory evoked potentials thus had a PPV of 0.36 (4/11) and a negative-predictive value (NPV) of 0.93 (14/15). Eighteen neonates (69 %) had brain injury on MRI; thus, MRI had a PPV of 0.28 (5/18) and an NPV of 1.00 (8/8). The authors concluded that neonates with HIE treated with hypothermia with bilateral absent N19 potentials may have a better prognosis than reported in the pre-hypothermia era; MRI also had a low PPV and high NPV. They stated that SEPs should be interpreted with caution in this new population and need to be re-evaluated in larger studies.
Visual Evoked Potentials for Evaluation of Birdshot Chorioretinopathy
Tzekov and Madow (2015) noted that birdshot chorioretinopathy (BSCR) is a rare form of autoimmune posterior uveitis that can affect the visual function and, if left untreated, can lead to sight-threatening complications and loss of central vision. These investigators performed a systematic search of the literature focused on visual electrophysiology studies, including ERG, electrooculography (EOG), and VEP, used to monitor the progression of BSCR and estimate treatment effectiveness. Many reports were identified, including using a variety of methodologies and patient populations, which made a direct comparison of the results difficult, especially with some of the earlier studies using non-standardized methodology. Several different electrophysiological parameters, such as EOG Arden's ratio and the mfERG response densities, are reported to be widely affected. However, informal consensus emerged in the past decade that the full-field ERG light-adapted 30-Hz flicker peak time is one of the most sensitive electrophysiological parameters. As such, it has been used widely in clinical trials to evaluate drug safety and effectiveness and to guide therapeutic decisions in clinical practice. The authors concluded that despite its wide use, a well-designed longitudinal multi-center study to systematically evaluate and compare different electrophysiological methods or parameters in BSCR is still lacking; but would benefit both diagnostic and therapeutic decisions.
Intraoperative Neuromonitoring During Implantation/Removal and Adjustment of Vertical Expandable Prosthetic Titanium Rib
Skaggs and colleagues (2009) stated that the vertical expandable prosthetic titanium rib (VEPTR) device is used in the treatment of thoracic insufficiency syndrome and certain types of early-onset spinal deformity. These researchers evaluated the risk of neurologic injury during surgical procedures involving use of the VEPTR and determined the effectiveness of intra-operative spinal cord neuro-monitoring (IONM). Data were collected prospectively during a multi-center study. Surgical procedures were divided into 3 categories:- primary device implantation,
- device exchange, and
- device lengthening.
Further retrospective evaluation was undertaken in cases of neurologic injury or changes detected with neuro-monitoring. There were 1,736 consecutive VEPTR procedures at 6 centers: 327 (in 299 patients) consisted of a primary device implantation, 224 were a device exchange, and 1,185 were a device lengthening. Peri-operative clinical neurologic injury was noted in 8 (0.5 %) of the 1,736 cases: these injuries were identified after 5 (1.5 %) of the 327 procedures for primary device implantation, 3 (1.3 %) of the 224 device exchanges, and none of the 1,185 device-lengthening procedures. Of the 8 cases of neurologic injury, 6 involved the upper extremity and 2 involved the lower extremity. The neurologic deficit was temporary in 7 patients and permanent in 1 patient, who had persistent neurogenic arm and hand pain; IONM demonstrated changes during 6 (0.3 %) of the 1,736 procedures: 5 (1.5 %) of the 327 procedures for primary device implantation and 1 (0.08 %) of the 1,185 device-lengthening procedures. The surgery was altered in all 6 cases, with resolution of the monitoring changes in 5 cases and persistent signal changes and a neurologic deficit (upper-extremity brachial plexopathy) in 1; 2 patients had false-negative results of monitoring of SEPs, and 1 had false-negative results of monitoring of SEPs and MVPs during implant surgery; 2 had a brachial plexopathy and 1 had monoplegia post-operatively, with all 3 recovering. The authors concluded that neurologic injury during VEPTR surgery occurred much more frequently in the upper extremities than in the lower extremities. The rates of potential neurologic injuries (neurologic injuries plus instances of changes detected by monitoring) during primary implantation of the VEPTR (2.8 %) and during exchange of the VEPTR (1.3 %) justified the use of IONM of the upper and lower extremities during those procedures. As neuro-monitoring did not demonstrate any changes in children without a previous VEPTR-related monitoring change and there were no neurologic injuries during more than 1,000 VEPTR-lengthening procedures, IONM may not be necessary during those procedures in children without a history of a neurologic deficit during VEPTR surgery.
Roper (2000) noted that the titanium rib procedure is a safe and effective way of surgically treating pediatric patients with thoracic insufficiency syndrome and scoliosis. As with any invasive surgical procedure, it is not without risks. This investigator explained the potential risks to neurological structures while outlining the surgical approach and the neurological anatomy in the vicinity of the implanted instrumentation. The types of potential nerve injury involve ischemia, trauma, compression, and stretch. Furthermore, a suitable compilation of modalities of IONM is recommended to detect and avoid long-term nerve or spinal cord insult. The authors concluded that overall, there are potential risks to the peripheral nerves and spinal cord during the implantation and subsequent lengthening of the vertical expandable prosthetic titanium rib (VEPTR) device. However, utilizing the appropriate IONM modalities as a tool and intervention may prevent or significantly reduce the severity of any post-operative deficit, thereby influencing the outcome and artificially raising the quantity of false-positive cases. An appropriate monitoring plan offers real-time feedback on a patient’s neurological conduction status. If potential compromise is communicated properly among the surgical team, it is possible to reverse trauma to nervous tissue so the insult is only temporary and does not become permanent. This is the goal of utilizing an appropriate IONM regimen during a VEPTR procedure. The author stated that IONM should be a part of the initial surgical implantation of the device as well as any VEPTR replacements of the devise as neurological risks are potentially present in all.
Intraoperative Somatosensory Evoked Potentials for Cochlear Implantation
American Academy of Neurology’s “Principles of Coding for Intraoperative Neurophysiologic Monitoring (IOM) and Testing” did not mention cochlear implantation.
American Speech-Language-Hearing Association (ASHA)’s Technical Report on “Cochlear Implants” did not mention somatosensory evoked potentials (SSEPs) as a management tool.
Motor Evoked Potentials for Evaluation of Wilson's Disease
Bembenek and colleagues (2015) noted that Wilson's disease (WD) is a metabolic brain disease resulting from improper copper metabolism. Although pyramidal symptoms are rarely observed, sub-clinical injury is highly possible as copper accumulates in all brain structures. The usefulness of MEPs in pyramidal tracts damage evaluation still appears to be somehow equivocal. These investigators searched for original papers assessing the value of transcranial magnetic stimulation elicited MEPs with respect to motor function of upper and lower extremity in WD. They searched PubMed for original papers evaluating the use of MEPs in WD using key words: "motor evoked potentials Wilson's disease" and "transcranial magnetic stimulation Wilson's disease”. These investigators found 6 articles using the above key words; 1 additional article and 1 case report were found while viewing the references lists. Thus, a total of 8 studies were included in this analysis; number of participants in studies was low and their clinical characteristic was variable. There were also differences in methodology. Abnormal MEPs were confirmed in 20 to 70 % of study participants; MEPs were not recorded in 7.6 to 66.7 % of patients; 4 studies reported significantly increased cortical excitability (up to 70 % of patients). Prolonged central motor conduction time was observed in 4 studies (30 to 100 % of patients). One study reported absent or prolonged central motor latency in 66.7 % of patients. The authors concluded that although MEPs may be abnormal in WD, this has not been thoroughly assessed. They stated that further studies are needed to evaluate MEPs' usefulness in assessing pyramidal tract damage in WD.
Ocular Vestibular Evoked Myogenic Potentials for the Diagnosis of Myasthenia Gravis
In a case-control, proof-of-principle study, Valko and colleagues (2016) examined if ocular vestibular evoked myogenic potentials (oVEMP) can be used to detect a decrement in the extra-ocular muscle activity of patients with myasthenia gravis (MG). A total of 27 patients with MG, including 13 with isolated ocular and 14 with generalized MG, and 28 healthy controls were included in this study. These investigators applied repetitive vibration stimuli to the forehead and recorded the activity of the inferior oblique muscle with 2 surface electrodes placed beneath the eyes. To identify the oVEMP parameters with the highest sensitivity and specificity, these researchers evaluated the decrement over 10 stimulus repetitions at 3 different repetition rates (3 Hz, 10 Hz, and 20 Hz). Repetitive stimulation at 20 Hz yielded the best differentiation between patients with MG and controls with a sensitivity of 89 % and a specificity of 64 % when using a unilateral decrement of greater than or equal to 15.2 % as cut-off. When using a bilateral decrement of greater than or equal to 20.4 % instead, oVEMP allowed differentiation of MG from healthy controls with 100 % specificity, but slightly reduced sensitivity of 63 %. For both cut-offs, sensitivity was similar in isolated ocular and generalized MG. The authors concluded that the findings of this study demonstrated that the presence of an oVEMP decrement is a sensitive and specific marker for MG. This test allowed direct and non-invasive examination of extra-ocular muscle activity, with similarly good diagnostic accuracy in ocular and generalized MG. They stated that oVEMP represents a promising diagnostic tool for MG. This study provided Class III evidence that oVEMP testing accurately identifies patients with MG with ocular symptoms (sensitivity 89 %, specificity 64 %). Well-designed studies are needed to confirm the diagnostic utility of oVEMP in clinical practice.
In an editorial that accompanied the afore-mentioned study, Prasad and Halmagyi (2016) stated that cohort studies are needed to evaluate the value of oVEMP in clinical practice, where a broader range of diagnostic possibilities leaves the clinician uncertain.
Vestibular Evoked Myogenic Potentials for the Diagnosis of Meniere's Disease or Delayed Endolymphatic Hydrops
Akkuzu et al (2006) examined the role of VEMP in benign paroxysmal positional vertigo (BPPV) and Meniere's disease, and ascertained if this type of testing is valuable for assessing the vestibular system. The 62 participants included 17 healthy controls and 45 other subjects selected from patients who presented with the complaint of vertigo (25 diagnosed with BPPV and 20 diagnosed with Meniere's disease). Vestibular evoked myogenic potentials were recorded in all subjects and findings in each patient group were compared with control findings. Vestibular evoked myogenic potentials for the 30 affected ears in the 25 BPPV patients revealed prolonged latencies in 8 ears and decreased amplitude in 1 ear (9 abnormal ears; 30 % of total). The recordings for the 20 affected ears in the Meniere's disease patients revealed 4 ears with no response, 6 ears with prolonged latencies (10 abnormal ears; 50 % of total). Only 2 (5.9 %) of the 34 control ears had abnormal VEMP. The rate of VEMP abnormalities in the control ears was significantly lower than the corresponding rates in the affected BPPV ears and the affected Meniere's ears that were studied (p = 0.012 and p < 0.001, respectively). The results suggested that testing of VEMP is a promising method for diagnosing and following patients with BPPV paroxysmal positional vertigo and Meniere's disease.
Egami and associates (2013) estimated the sensitivity and specificity of VEMPs in comparison with caloric test in diagnosing MD among patients with dizziness. Data were retrospectively collected from 1,170 consecutive patients who underwent vestibular tests. Among them, 114 patients were diagnosed as having unilateral definite MD; VEMPs in response to clicks and short tone burst stimulation as well as caloric tests were performed. The sensitivity and specificity of each test were evaluated. The results of each test were compared with hearing level and staging of MD. The sensitivity and specificity of VEMPs were 50.0 % and 48.9 %, while those of the caloric test were 37.7 % and 51.2 %, respectively. There was no significant difference in hearing level between patients appropriately or inappropriately identified by VEMPs, whereas there was a significant difference in those of the caloric test. Combined use of VEMP and caloric test increased the sensitivity to 65.8 %. The authors concluded that although the sensitivity and specificity of VEMPs in diagnosing MD were not high, they were comparable to those of caloric test. They stated that VEMPs as well as caloric testing may give additional information as part of a diagnostic test battery for detecting vestibular abnormalities in MD.
In a systematic review and meta-analysis, Zhang and colleagues (2015) evaluated the clinical diagnostic value of VEMPs for endolymphatic hydrops (EH). The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio (OR) and area under summary receiver operating characteristic curves (AUC) were calculated. Subgroup analysis and publication bias assessment were also conducted. The pooled sensitivity and the specificity were 49 % (95 % CI: 46 % to 51 %) and 95 % (95 % CI: 94 % to 96 %), respectively. The pooled positive likelihood ratio was 18.01 (95 % CI: 9.45 to 34.29) and the pooled negative likelihood ratio was 0.54 (95 % CI: 0.47 to 0.61); AUC was 0.78 and the pooled diagnostic OR of VEMPs was 39.89 (95 % CI: 20.13 to 79.03). The authors concluded that the findings of the present meta-analysis showed that VEMPs test alone is not sufficient for the diagnosis of MD or delayed EH, but that it might be an important component of a test battery for diagnosing MD or delayed EH. Moreover, VEMPs, due to its high specificity and non-invasive nature, might be used as a screening tool for EH.
Furthermore, an UpToDate review on “Meniere disease” (Moskowitz and Dinces, 2016) states that “Meniere disease is a clinical diagnosis. Although not diagnostic, patients should undergo audiometry, vestibular testing, and MRI to rule out other causes of symptoms. The vestibular evoked myogenic potential (VEMP) test may be useful for monitoring disease progression”.
Intraoperative Somatosensory Evoked Potentials During Cervical Facet Injections
An UpToDate review on “Subacute and chronic low back pain: Nonsurgical interventional treatment” (Chou, 2017) does not mention “neuroimaging or intraoperative monitoring” for facet joint injection.
Intraoperative Somatosensory Evoked Potentials During Decompression of the Trigeminal Nerve
An UpToDate review on “Trigeminal neuralgia” (Bajwa et al, 2017) does not mention intraoperative monitoring or intraoperative SSEP monitoring.
Intraoperative Somatosensory Evoked Potentials During Rotator Cuff Repair
An UpToDate review on “Management of rotator cuff tears” (Martin and Martin, 2017) does not mention intraoperative SSEP monitoring.
Cervical and Ocular Vestibular Evoked Myogenic Potential Testing
On behalf of the American Academy of Neurology (AAN), Fife and colleagues (2017) reviewed the evidence and made recommendations regarding the diagnostic utility of cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP, respectively). Four questions were asked:- does cVEMP accurately identify superior canal dehiscence syndrome (SCDS)?
- does oVEMP accurately identify SCDS?
- for suspected vestibular symptoms, does cVEMP/oVEMP accurately identify vestibular dysfunction related to the saccule/utricle? and
- for vestibular symptoms, does cVEMP/oVEMP accurately and substantively aid diagnosis of any specific vestibular disorder besides SCDS?
The guideline panel identified and classified relevant published studies (January 1980 to December 2016) according to the 2004 AAN process. The following recommendations were provided:
- Level C positive: Clinicians may use cVEMP stimulus threshold values to distinguish SCDS from controls (2 Class III studies) (sensitivity 86 % to 91 %, specificity 90 % to 96 %). Corrected cVEMP amplitude may be used to distinguish SCDS from controls (2 Class III studies) (sensitivity 100 %, specificity 93 %). Clinicians may use oVEMP amplitude to distinguish SCDS from normal controls (3 Class III studies) (sensitivity 77 % to 100 %, specificity 98 % to 100%). oVEMP threshold may be used to aid in distinguishing SCDS from controls (3 Class III studies) (sensitivity 70 % to 100 %, specificity 77 % to 100 %).
- Level U: Evidence is insufficient to determine whether cVEMP and oVEMP can accurately identify vestibular function specifically related to the saccule/utricle, or whether cVEMP or oVEMP is useful in diagnosing vestibular neuritis or Meniere disease.
- Level C negative: It has not been demonstrated that cVEMP substantively aids in diagnosing benign paroxysmal positional vertigo, or that cVEMP or oVEMP aids in diagnosing/managing vestibular migraine.
Intra-Operative Neuromonitoring During Carpal Tunnel Release
An UpToDate review on “Surgery for carpal tunnel syndrome” (Hunter and, Simmons, 2018) does not mention neuromonitoring, neuromuscular junction monitoring, or somatosensory evoked potential monitoring as a management tool.
Intra-Operative Neuromonitoring During Femoroacetabular Surgery
Ochs and associates (2012) noted that arthroscopic hip surgery is used to treat many of the causes of hip pain, hip instability, and hip disorders. Hip pain and instability are often caused by injuries to the acetabular labrum. Repairing labral tears, suturing, and debridement involve stabilizing the hip and placing the operative side leg in traction to allow for instrument clearance and to avoid iatrogenic injury to the chondral surfaces. This places the sciatic nerve in a stretched position and may cause temporary or permanent nerve injury. Transient neuropraxia is the most common injury occurring in 5 % of the patients undergoing arthroscopic hip surgery. In this study, a total of 35 patients (24 women and 11 men, a total of 36 surgeries) were monitored with IONM using SSEPs during hip arthroscopy for labral repair and femoral head osteoplasty. They ranged in age from 15 to 59 years; mean age of 39.81 years. During surgery 19 (54 %) patients experienced significant SSEP waveform changes. Time from placement of traction to loss of signals in those patients experiencing SSEP changes ranged from 7 mins to 46 mins. Recovery of SSEP signals ranged from 2 mins to over 15 mins when the traction of the leg was released. Surgeries ranged from 2 to 4 hours; mean of 2.78 hours. The authors concluded that these findings showed that neuromonitoring during hip arthroscopic labral repair and debridement procedures might be useful to prevent temporary and permanent neural tissue injuries.
Hesper and colleagues (2017) stated that nerve injuries can occur from major hip surgeries, and some may be significant. These investigators examined the feasibility and safety of neuromonitoring during hip preservation surgery and the incidence of alerting events during such monitoring. A total of 25 adult patients underwent surgical hip dislocation for femoro-acetabular impingement (FAI). Upper and lower extremity SSEPs, lower extremity transcranial MEPs, and lower extremity EMG were recorded. They observed a temporary reduction of the monitored parameters in 12 patients (48 %) during surgery. There were no clinically significant neurological deficits post-operatively in any cases. The authors concluded that neuromonitoring demonstrated events during hip surgery in this case-series study. Although it may not be practical to use neuromonitoring in all major hip surgeries, it may be prudent from the perspective of patient safety to use it in high-risk cases, including those requiring prolonged surgical time; in patients with high body mass index (BMI), excessive deformity correction, and pre-existing neuropathy; and in revision cases, among others.
The authors stated that this study had several drawbacks. With a sample size of 25 patients, this rather small study group did not allow for proof of reliability of IONM to predict permanent impairments of nerve function during this particular procedure, as sciatic nerve injury with post-operative deficiency in neuromuscular function has been described in less than 1% of cases after surgical hip dislocation. Furthermore, as alerting events apparently appeared to be dependent on leg positioning while the hip was dislocated, different surgical assistants (who were holding the legs during these cases) might have possibly biased these findings. However, all surgeries were performed by 1 single surgeon, and efforts were made to ensure similar patient positioning during each case. Because of the need of muscle relaxants for endotracheal intubation, ease of dislocation and surgical exposures, and less tension on muscle structures, intraoperative EMG and TcMEP evaluation done during the usage of muscle relaxants might have been impaired. Until the relaxants wore off, SSEPs were the predominant predictor of nerve injury. However, evaluation of SSEPs were based on calculated averages that were recorded, and thus, transient nerve injury might have sometimes occurred several minutes before notification. In a study by Hilibrand et al (2004), changes in SSEPs were shown to occur with an average delay of 16 minutes after alterations in MEPs were noted. With respect to the present findings, these results indicated that, in case of an alerting event, transient sciatic nerve injury might occur earlier than the average time of 36.7 ± 13.9 minutes that was noted in this study, and should likely be considered as such in dealing with the event. However, because no patient exhibited a post-operative deficit in neuromuscular function, it appeared unlikely that irreversible neurological injury had occurred at that point, that is, within the time span of an event in these patients.
Intra-Operative Neuromonitoring During Rotator Cuff Repair
An UpToDate review on “Management of rotator cuff tears” (Martin and Martin, 2018) does not mention intra-operative neuromonitoring as a management tool.
Intra-Operative Neuromonitoring During Tethered Cord Release
Sala and colleagues (2002) performed a critical analysis of the role of intraoperative neurophysiological monitoring (INM) during various neurosurgical procedures, emphasizing the aspects that mainly concern the pediatric population. Original papers related to the field of intraoperative neurophysiology were collected using Medline; INM consists of monitoring (continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (functional identification and preservation of anatomically ambiguous nervous tissue) techniques. These investigators attempted to delineate indications for intraoperative neurophysiological techniques according to their feasibility and reliability (specificity and sensitivity). In compiling this review, controversies about indications, methodologies and the usefulness of some INM techniques have surfaced. These discrepancies were often due to lack of familiarity with new techniques in groups from around the globe. Accordingly, internationally accepted guidelines for INM are still far from being established. Nevertheless, the studies reviewed provide sufficient evidence to enable clinicians to make the following recommendations.
- INM is mandatory whenever neurological complications are expected on the basis of a known pathophysiological mechanism. INM becomes optional when its role is limited to predicting post-operative outcome or it is used for purely research purposes.
- INM should always be performed when any of the following are involved: supratentorial lesions in the central region and language-related cortex; brain stem tumors; intramedullary spinal cord tumors; conus-cauda equina tumors; rhizotomy for relief of spasticity; spina bifida with tethered cord.
- Monitoring of MEPs is now a feasible and reliable technique that can be used under general anesthesia. MEP monitoring is the most appropriate technique to assess the functional integrity of descending motor pathways in the brain, the brain stem and, especially, the spinal cord.
- Monitoring of SEP is of value in assessment of the functional integrity of sensory pathways leading from the peripheral nerve, through the dorsal column and to the sensory cortex. SEPs cannot provide reliable information on the functional integrity of the motor system (for which MEPs should be used).
- Monitoring of brain stem auditory evoked potentials remains a standard technique during surgery in the brain stem, the cerebellopontine angle, and the posterior fossa.
- Mapping techniques (such as the phase reversal and the direct cortical/subcortical stimulation techniques) are invaluable and strongly recommended for brain surgery in eloquent cortex or along subcortical motor pathways.
- Mapping of the motor nuclei of the 8th, 9th to 10th and 12th cranial nerves on the floor of the 4th ventricle is of great value in identification of "safe entry zones" into the brain stem. Techniques for mapping cranial nerves in the cerebellopontine angle and cauda equina have also been standardized. Other techniques, although safe and feasible, still lack a strong validation in terms of prognostic value and correlation with the post-operative neurological outcome. These techniques include monitoring of the bulbo-cavernosus reflex, monitoring of the corticobulbar tracts, and mapping of the dorsal columns. These techniques, however, are expected to open up new perspectives in the near future.
Paradiso and associates (2005) stated that during complex micro-neurosurgery performed in patients with tethered cord syndrome (TCS), the conus medullaris and the roots that innervate the lower limbs, bladder and bowel are potentially exposed to damage. The aim of multi-modality IOM is to reduce the risk of inadvertent injury of neural tissue. These researchers simultaneously recorded tibial nerve SSEPs from the scalp and free-run EMG of limb muscles supplied by L2 to S2 roots, anal and urethral sphincters. They also identified critical neural structures in the operative field, including the conus and exiting nerve roots, with a nerve stimulator to evoke EMG; SSEPs assessed the sensory pathways mainly mediated by the S1 roots. Continuous EMG provided the surgeon with immediate auditory feedback resulting from irritative discharges triggered by manipulation of nerve fibers. Micro-stimulation can distinguish the filum terminale, scar tissue and invasive tumors from functional neural tissue, thus minimizing the risk of iatrogenic injury. The authors concluded that multi-modality IOM proved a valuable adjunct to micro-neurosurgery of the lumbosacral spine.
Husain and Shah (2009) noted that IONM is used in surgery for TCS. These researchers determined if IONM is helpful in identifying which patients would have worsening symptoms after surgery. The spinal cord was stimulated before and after untethering until a motor response was obtained. The pre- and post-operative neurologic examination findings were noted. The motor response thresholds before and after untethering were compared using Student t-tests. A total of 40 patients were identified; 37 had higher motor response thresholds before untethering, whereas in 3 thresholds were higher after untethering. Of the 37 patients, 2 had worsening of motor function. All 3 patients with higher thresholds after untethering had worsening of motor function (p < 0.0001). The authors concluded that an increase in the motor response threshold after surgical release of tethered cord syndrome indicated possible worsening of clinical symptoms; spinal cord stimulation during TCS surgery may help predict neurologic outcome.
Beyazova and co-workers (2010) stated that the TCS refers to a variety of lesions that can cause the conus medullaris to be low-lying or incapable of movement within the spinal canal. Permanent or temporary neurological complications were reported following surgical release. In this report, peri- and post-operative results in cases with TCS that were followed by multi-modal IONM (MIONM) methods were presented. An IONM system (Nicolet CR Endeavor) was used for monitoring during TCS surgery; SEPs, MEPs, direct nerve root/rootlet stimulation, free-run EMG and F-waves were used during TCS surgery of 10 cases to prevent possible nerve injuries. MEP and SEP recordings did not change in any of the cases during surgery. The nervous tissue was identified and differentiated from connective tissue in 3 cases when motor responses were elicited with direct stimulation of nerve roots. None of the cases had neurological deficits following the operation. The authors concluded that direct nerve root/rootlet stimulation should be one of the components of MIONM during surgery for TCS to prevent post-operative neurological deficits.
Intra-Operative Neuromonitoring During Thyroidectomy and Thyroid Re-Operations
Barczynski and colleagues (2013) stated that IONM during thyroid surgery has gained widespread acceptance as an adjunct to the gold standard of visual identification of the recurrent laryngeal nerve (RLN). Contrary to routine dissection of the RLN, most surgeons tend to avoid rather than routinely expose and identify the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy or parathyroidectomy. IONM has the potential to be utilized for identification of the EBSLN and functional assessment of its integrity; therefore, IONM might contribute to voice preservation following thyroidectomy or parathyroidectomy. These investigators reviewed the literature and the cumulative experience of the multi-disciplinary International Neural Monitoring Study Group (INMSG) with IONM of the EBSLN. A systematic search of the Medline database (from 1950 to the present) with pre-defined search terms (EBSLN, superior laryngeal nerve, stimulation, neuromonitoring, identification) was undertaken and supplemented by personal communication between members of the INMSG to identify relevant publications in the field. The hypothesis explored in this review was that the use of a standardized approach to the functional preservation of the EBSLN could be facilitated by application of IONM resulting in improved preservation of voice following thyroidectomy or parathyroidectomy. Level of Evidence: V.
Pisanu and co-workers (2014) stated that the role of IONM of the RLN during thyroid surgery is still debatable. In a meta-analysis, these investigators evaluated the potential improvement of IONM versus RLN visualization alone (VA) in reducing the incidence of vocal cord palsy. A literature search for studies comparing IONM versus VA during thyroidectomy was performed. Studies were reviewed for primary outcome measures: overall, transient, and permanent RLN palsy per nerve and per patients at risk; and for secondary outcome measures: operative time; overall, transient and permanent RLN palsy per nerve at low and high risk; and the results regarding assistance in RLN identification before visualization. A total of 20 studies comparing thyroidectomy with and without IONM were reviewed: 3 prospective, randomized trials, 7 prospective trials, and 10 retrospective, observational studies. Overall, 23,512 patients were included, with thyroidectomy performed using IONM compared with thyroidectomy by VA. The total number of nerves at risk was 35,513, with 24,038 nerves (67.7 %) in the IONM group, compared with 11,475 nerves (32.3 %) in the VA group. The rates of overall RLN palsy per nerve at risk were 3.47 % in the IONM group and 3.67 % in the VA group. The rates of transient RLN palsy per nerve at risk were 2.62 % in the IONM group and 2.72 % in the VA group. The rates of permanent RLN palsy per nerve at risk were 0.79 % in the IONM group and 0.92 % in the VA group. None of these differences was statistically significant, and no other differences were found. The authors concluded that the current review with meta-analysis showed no statistically significant difference in the incidence of RLN palsy when using IONM versus VA during thyroidectomy. However, they noted that these results must be approached with caution, as they were mainly based on data coming from non-randomized observational studies. These researchers stated that further studies including high-quality multi-center, prospective, randomized trials based on strict criteria of standardization and subsequent clustered meta-analysis are needed to verify the outcomes of interest.
Barczynski and associates (2016) noted that surgical management of the EBSLN during thyroidectomy is complex. These investigators hypothesized that there exist variations in surgical behaviors patterns in the management of the EBSLN during thyroidectomy. They carried out a prospective Web-based anonymous survey. The survey, consisting of 22 questions including surgeon demographics, laryngeal examination before and after surgery, and utilization of IONM for the management of the RLN and the EBSLN, was sent to 673 surgeons world-wide with known interest in thyroid surgery. A total of 170/673 (25.3 %) surgeons from 5 continents with low-volume (11.2 %), moderate-volume (27.2 %), and high-volume practices (61.5 %) completed the survey. Laryngeal pre-operative examination was performed by 94 % of respondents. IONM was utilized in the RLN management by 95 % of respondents. IONM was used for identification of the EBSLN by 26.3 % of low-volume versus 68.4 % of high-volume surgeons (p = 0.004), and 93 % of respondents felt EBSLN identification with IONM as necessary in voice professionals. Staged thyroidectomy was performed for benign disease by 89.5 % of low-volume versus 63.2 % of high-volume surgeons (p = 0.031). Post-thyroid surgery laryngeal examination was performed by 36.8 % of low-volume versus 64.9 % of high-volume surgeons (p = 0.032). The authors concluded that laryngeal examination and IONM was used frequently. However, the exact pattern of utilization varied notably with demographic information. Generally, high-volume surgeons, those with otolaryngology background, and younger surgeons more commonly utilized IONM according to existing international neural monitoring study group guidelines. These researchers stated that prospective multi-center studies are needed to guide an evidence-based management of the EBSLN during thyroidectomy.
Yang and colleagues (2017) noted that IONM has been a commonly used technology during thyroid surgery aimed at reducing the incidence of recurrent laryngeal nerve palsy (RLNP), which is a severe complication and leads to significant impacts on a patient's life. In order to give a comprehensive assessment for potential benefits and disadvantage of IONM, this meta-analysis and systematic review discussed RLNP rate, predictive power, continuous IONM (CIONM), and emphasized application during thyroid cancer surgeries. A literature search was performed in the following electronic databases: PubMed, Embase, and the Cochrane library from January 1, 2004 to July 30, 2016. After applying inclusion and exclusion criteria, a total of 24 studies, including 4 prospective randomized trials, were selected. Heterogeneity of studies was checked by the Cochran Q test. Publication bias was assessed by funnel plots with Egger's linear regression test of asymmetry; OR was calculated by random effects model. Overall, 9,203 patients and 17,203 nerves at risk (NAR) were included. Incidence of overall, transient, and persistent RLNP in IONM group were, respectively, 3.15 %, 1.82 %, and 0.67 %, whereas for the ID group, they were 4.37 %, 2.58 %, and 1.07 %. The summary OR of overall, transient, and persistent RLNP compared using IONM and ID were, respectively, 0.81 (95 % CI: 0.66 to 0.99), 0.76 (95 % CI: 0.61 to 0.94), and 0.78 (95 % CI: 0.55 to 1.09). The authors concluded that the presented data showed benefits of reducing RLNP rate by using IONM, but without statistical significance for persistent RLNP rate. For patients with thyroid cancer who underwent total thyroidectomy, the use of IONM may improve the outcome by reducing amount of residual thyroid tissue. However, no benefits were found for thyroid re-operation; visual identification and careful dissection remain standard for this challenging procedure. In addition, the relative low positive predictive power indicated intermittent IONM (IIONM) may not be reliable; but CIONM was showed to be a more promising method, with prudent approach.
Motos-Mico and associates (2017) stated that IONM of the RLN in thyroid surgery facilitates the identification of anatomical structures in cervical endocrine surgery reducing the frequency of vocal cord paralysis. An In an observational, descriptive, prospective study, these investigators examined the normal electrophysiological values of the vagus nerve and RLN before and after thyroid surgery, and compared rates of injury of RLN before and after the introduction of the IONM in thyroid surgery. This trial included a total of 490 patients, and was carried out between 2003 to 2010; surgery was performed on 411 patients (703 nerves at risk) with systematic identification of RLNs. Between 2010 to 2011 neuromonitorization was also systematically performed on 79 patients. Before the introduction of IONM of 704 nerves at risk, there were 14 RLN injuries. Since 2010, after the introduction of the intraoperative neuromonitoring in thyroid surgery, there has been no nerve injury in 135 nerves at risk. The authors concluded that the systematic identification of the RLN is the “gold standard” in thyroid surgery and IONM of nerves can never replace visual nerve identification but can complement it.
Stopa and Barczynski (2017) stated that the diagnostic accuracy of IONM of the RLN remains controversial. In a prospective study, these investigators examined IONM diagnostic accuracy in prognostication of post-operative nerve function in thyroid surgery. This trial was conducted in 2011 to 2013; a total of 500 consenting patients qualified for total thyroidectomy with IONM (1,000 nerves at risk) using NIM 3.0 Response equipment were included. Laryngoscopy was used to evaluate and follow-up RLN injury. The primary outcome was diagnostic accuracy of IONM. The receiver operating characteristics (ROC) were used for evaluation of IONM diagnostic accuracy. Loss of signal (LOS) occurred in 31 cases, including 25 patients with LOS and corresponding vocal fold paresis found in post-operative laryngoscopy (2.5 %), including 20 (2.0 %) temporary and 5 (0.5 %) permanent nerve lesions. The following diagnostic accuracy values were calculated for the criterion recommended by INMSG (V2 amplitude of less than or equal to 100 μV): sensitivity of 92.0 %, specificity of 99.3 %, PPV of 76.7 %, and NPV of 99.8 %. The ROC curve analysis allowed for calculation of the most optimal criterion in prognostication of post-operative vocal fold paresis, namely, V2 amplitude of less than or equal to 189 μV. For this criterion, PPV was 77.4 %, while NPV was 99.9 %. The authors concluded that aAdherence to the standardized protocol recommended by the International Neural Monitoring Study Group allowed for optimizing predictive values of IONM in prognostication of post-operative RLN function. Any changes in the cut-off values for the definition of LOS only marginally improve PPV and NPV of IONM and need to be carefully assessed in multi-center studies.
The authors stated that despite a prospective design, the current study had several drawbacks. Not all eligible patients were included, as the employment of IONM in Poland is not reimbursed by the Polish National Health Fund, which is the main reason for using this technique on select patients depending on the individual surgeon’s preferences and availability of the equipment. The operations were performed not by 1, but 2 surgeons. However, in order to minimize the risk of any bias, all the surgeons involved in this study had a comparable background experience both in thyroid surgery and utilization of IONM during thyroidectomy. Post-operative laryngoscopy was not performed immediately after surgery in the recovery room, but at post-operative day 1, which in theory might have led to under-estimation of the prevalence of short-lasting transient nerve injuries.
Calo and colleagues (2017) evaluated the diagnostic accuracy of IONM in predicting post-operative nerve function during thyroid surgery and its consequent ability to assist the surgeon in intra-operative decision-making. A total of 2365 consecutive patients were submitted to thyroidectomy by the same surgical team. Group A included 1,356 patients (2,712 nerves at risk) in whom IONM was utilized, and Group B included 1,009 patients (2,018 nerves at risk) in whom IONM was not utilized. In Group A, loss of signal (LOS) was observed in 37 patients; there were 29 true-positive, 1,317 true-negative, 8 false-positive, and 2 false-negative cases. Accuracy was 99.3 %, PPV was 78.4 %, NPV was 99.8 %, sensitivity was 93.6 %, and specificity was 99.4 %. A total of 29 (2.1 %) cases of unilateral paralysis were observed, 23 (1.7 %) of which were transient and 6 (0.4 %) of which were permanent. Bilateral palsy was observed in 2 (0.1 %) cases requiring a tracheostomy. In Group A, 31 (2.3 %) injuries were observed, 25 (1.8 %) of which were transient and 6 (0.4 %) of which were permanent. In Group B, 26 (2.6 %) unilateral paralysis cases were observed, 20 (2 %) of which were transient and 6 (0.6 %) of which were permanent; bilateral palsy was observed in 2 (0.2 %) cases. In Group B, 28 (2.8 %) injuries were observed, 21 (2.1 %) of which were transient and 7 (0.7 %) of which were permanent. Differences between the 2 groups were not statistically significant. The authors concluded that these findings showed that IONM had a very high sensitivity and NPV, but also good specificity and PPV. For these reasons, in selected patients with LOS, the surgical strategy should be reconsidered. However, patients need to be informed pre-operatively about potential strategy changes during the planned bilateral surgery. These researchers stated that future larger, multi-center studies are needed to confirm the benefits of this therapeutic strategy.
Wojtczak and associates (2018) examined the usefulness of IONM in identifying anatomical variants of the RLN during thyroidectomies, with emphasis on the nerve's relationship to the inferior thyroid artery (ITA), Zuckerkandl's tubercle, non-RLNs (NRLNs), and extra-laryngeal bifurcation. A total of 128 subjects undergoing surgery for thyroid disorders were enrolled in the study, and the course and anatomical variants of RLN were assessed with IONM application. The standard relationship between RLN and ITA was that the artery and nerve intersect (100 %). The right RLN was below the ITA in 76.67 % of the patients, and the left RNL was below it in 75.81 %. There were no statistically significant differences in the relationship between RLN and ITA on the 2 sides; and gender did not significantly influence the relationship between the RLN and ITA on either side. In 1 patient a non-recurrent inferior laryngeal nerve was present on the right side (0.83 %); RLN bifurcation was observed in 33.33 % of the patients on the right and in 19.35 % on the left side; the difference between sides was statistically significant (p < 0.05). Posterior tubercle (Zuckerkandl's tubercle) was observed on the right in 83 % of the subjects and on the left in 69 %. The age, thyroid volume and body mass index (BMI) did not influence the size of the tumor. The authors concluded that the utilization of IONM of the RLN in thyroid surgery added a new dimension to the standard of visual nerve identification allowing for functional nerve testing at the most vulnerable area of the dissection: at the level of Berry's ligament, posterior tubercle (Zuckerkandl's tubercle) and crossing of the RLN with the inferior thyroid artery.
The authors stated that this study had 2 main drawbacks. First of all the study group comprised of 128 patients and hence it could be considered a relatively small study. Second, all these anatomical variants were observed by a single high-volume thyroid surgeon, which may be difficult to follow by low-volume thyroid surgeons.
Mirallie and co-workers (2018) stated that the impact of IONM on RLNP remains debated. In a prospective, multi-center, study, these researchers evaluated the potential protective effect of IONM on RLN during total thyroidectomy. The use of IONM was left at the surgeons' choice. Post-operative laryngoscopy was performed systematically at day 1 to 2 after operation and at 6 months in case of post-operative RLNP. Uni-variate and multi-variate analyses and propensity score (sensitivity analysis) were performed to compare RLNP rates between patients operated with or without IONM. Among 1,328 patients included (women 79.9 %, median age of 51.2 years, median BMI of 25.6 kg/m2), 807 (60.8 %) underwent IONM. Post-operative abnormal vocal cord mobility was diagnosed in 131 patients (9.92 %), including 69 (8.6 %) and 62 (12.1 %) in the IONM and non-IONM groups, respectively; IONM was associated with a lesser rate of RLNP in uni-variate analysis (OR = 0.68, 95 % CI: 0.47 to 0.98, p = 0.04); but not in multi-variate analysis (OR = 0.74, 95 % CI: 0.47 to 1.17, p = 0.19), or when using a propensity score (OR = 0.76, 95 % CI: 0.53 to 1.07, p = 0.11). There was no difference in the rates of definitive RLNP (0.8 % and 1.3 % in IONM and non-IONM groups respectively, p = 0.39). The sensitivity, specificity, PPV and NPV of IONM for detecting abnormal post-operative vocal cord mobility were 29 %, 98 %, 61 %, and 94 %, respectively. The authors concluded that the use of IONM did not decrease post-operative RLNP rate. Due to its high specificity, however, IONM was useful to predict normal vocal cord mobility.
Furthermore, an UpToDate review on “Initial thyroidectomy” (Wang et al, 2018) states that “Intraoperative nerve monitoring (IONM) has been introduced with the goal of reducing the rate of RLN injury. Although its routine use remains controversial, it could potentially assist in the identification, dissection, and prediction of postoperative function of the RLN”.
Wojtczak and associates (2017) stated that thyroid re-operations are at a high risk of RLN injury. In a retrospective, cohort study, these investigators examined if the use of IONM could aid in the RLN identification and minimize the risk of its injury, in comparison with visual RLN identification. This trial consisted patients who underwent thyroid re-operations with and without the use of IONM. Primary end-point was the RLN identification rate. The study entailed 61 patients undergoing thyroid re-operation among whom 24 were operated on with visual RLN identification only, while 37 procedures used IONM. In the non-monitored re-operations, 44.4 % of the RLN were visually identified, as opposed to 91.6 % in the IONM group (p < 0.001). Transient paresis occurred in 3 nerves with visualization (6.6 %), and in 1 in IONM group 1.6 % (p = 0.185). Permanent paresis occurred in the group with visualization (6.6 %), as opposed to none with IONM. The extent of resection in both groups was significantly different (p = 0.043). Total, near-total thyroidectomies, Dunhill operations and subtotal thyroidectomies were performed in 71, 17, 4, and 8 % in the visualization group, and in 94, 0, 3, and 3 %, respectively, in the IONM group. A non-anatomical RLN course was observed in 80 % of the re-operations with IONM. The authors concluded that thyroid re-operation should be performed using IONM, because it allowed for a significantly improved RLN identification rate and a significantly more radical resection.
The authors stated that there is currently no hard evidence that IONM could diminish the prevalence of permanent vocal fold palsy, but more than 90 % of the respondents in the most recent international survey on the identification and neural monitoring of the EBSLN during thyroidectomy emphasized their confidence in IONM, and listed re-operative thyroid cases as the top indication – far higher than any other clinical situation – for the use of this technique during thyroid surgery. Furthermore, these investigators noted that there is no consensus regarding the utility of IONM and its role is still evolving; i is not a standard of care in the majority of countries.
Sun and colleagues (2017) noted that the rate of RLNP is especially high in thyroid re-operations. In a meta-analysis, these researchers examined if IONM reduces the prevalence of RLNP in thyroid re-operations. A systematic literature search was conducted in the PubMed, SCIE and Wan Fang databases for studies published up to August 31, 2016. All data were analyzed using STATA (version 11) software. Publication bias was assessed using Begg's funnel plot and Egger's test, and sensitivity analysis was performed. A total of 9 studies including 2,436 at-risk nerves met the inclusion criteria. The results were presented as pooled RRs with 95 % CI. The overall RLNP rate was significantly lower in re-operations conducted with IONM than in those conducted without IONM (RR = 0.434, 95 % CI: 0.206 to 0.916, p = 0.029). High heterogeneity was found (I2 = 70.2 %, p = 0.001). The rates of transient RLNP with and without IONM did not differ significantly (RR = 0.607, 95 % CI: 0.270 to 1.366, p = 0.227). The heterogeneity was high (I2 = 67.4 %, p = 0.005). However, IONM was significantly associated with a reduction in permanent RLNP (RR = 0.426, 95 % CI: 0.196 to 0.925, p = 0.031). No significant heterogeneity was found (I2 = 13.7 %, p = 0.325). Funnel plots for overall and transient RLNP showed a possible publication bias. The authors concluded that IONM was associated with a reduction in overall and permanent RLNP in thyroid re-operations. However, these investigators stated that given the limited sample size and heterogeneity in this meta-analysis, further studies are needed to confirm these preliminary findings.
Intra-Operative Neuromonitoring During Total Knee Arthroplasty / Replacement
An UpToDate review on “Total knee arthroplasty” (Martin and Roe, 2018) does not mention intra-operative neuromonitoring as a management tool.
Evoked Potential Monitoring During Degenerative Cervical Spine Surgery
Di Martino and colleagues (2019) stated that intraoperative SSEP and TcMEP monitoring are frequently used in spinal as well as spinal cord surgery for so-called IONM, while the combination of these techniques is known as concomitant multi-modal intraoperative monitoring (MIOM). These investigators collected available evidence concerning use of IONM and MIOM in cervical decompression surgery in the degenerative setting and identified the best practice to be advocated. They carried out a review of the PubMed and Medline databases and Cochrane Central Registry of Controlled Trials. Studies were included if they involved patients who underwent cervical spine decompression surgery for degenerative stenosis with use of IONM or MIOM and where sensitivity/specificity was reported. In the identified studies, the sensitivity of SSEP was estimated to be between 22 % and 100 % with constant specificity of 100 % . In the included studies, the sensitivity of MEP was estimated to be between 78 % and 100 % with specificity ranging from 83.2 % to 100 %. The authors concluded that on the basis of available evidence, MIOM could be a helpful tool in decompression cervical spine surgery in patients affected by degenerative spinal stenosis, since it was associated with high specificity and sensitivity for detection of intraoperative neural damage. However, these researchers stated that given the lack of appropriate evidence, they recommended that better and more focused studies be performed to examine if the combination of SSEP and MEP is more sensitive and specific than either method alone. Furthermore, evidence concerning appropriate selection of patients in whom monitoring is indicated is still lacking, and this should be a focus of future studies on this topic.
Intraoperative Neuromonitoring During Total Hip Replacement
Overzet et al (2018) noted that arthroscopic hip surgery is performed routinely for the treatment of various hip disorders. Leg traction during labral tear repair, femoroplasty, and acetabuloplasty for hip stabilization can stretch the peripheral nerves. This may cause temporary or permanent nerve injury. This study examined the benefit of utilizing multi-modality intraoperative neurophysiological monitoring (IONM) during hip surgical procedures. They performed a retrospective review of 10 arthroscopic hip surgeries with neurophysiological monitoring at 1 medical center. Subjects consisted of 6 women and 4 men (mean age of 48.9 years). The procedures were equally divided into left and right-sided procedures; IONM setup included posterior tibial, peroneal, and femoral or saphenous nerve SSEPs, transcranial electrical MEP (TCeMEP), train of 4(TOF), and EMG from the lower extremities. All patients exhibited changes in IONM data during the surgical procedure. Changes in the latency and amplitude or loss of the lower SSEPs on the surgical side occurred in 36 % of the monitorable SSEPs. The surgeon instructed the team to reduce the leg lengthening by removing traction when changes were observed. The SSEPs exhibited a full recovery in 75 % of the affected lower extremity SSEPs. In the 2 instances of non-recovery, the SSEP responses remained increased in latency or decreased in amplitude at closing, but the waveform was intact. There were 5 instances of complete loss of the waveform (4 in the ipsilateral leg, and 1in the contralateral leg) with recovery after traction was reduced. TCeMEP changes occurred in 53 % of the ipsilateral lower muscles monitored. Many of the TCeMEP changes were attributed to ischemia of the feet and could not be resolved intraoperatively. The authors concluded that multi-modality IONM can be a beneficial and protective tool during surgical procedures involving hip and acetabular areas. Early identification of changes in EPs during hip arthroscopy surgeries could minimize post-operative neurological deficits due to peripheral nerve injury and leg ischemia. This was a small study (n = 10) on patients undergoing arthroscopic hip surgeries; not total hip replacement.
Furthermore, an UpToDate review on “Total hip arthroplasty” (Erens et al, 2019) does not mention intraoperative neuromonitoring as a management tool.
Visual Evoked Potential for Evaluation of Neuromyelitis Optica Spectrum Disorder
Ringelstein and colleagues (2020) examined if patients with neuromyelitis optica spectrum disorder (NMOSD) develop sub-clinical visual pathway impairment independent of acute attacks. A total of 548 longitudinally assessed full-field VEP of 167 patients with NMOSD from 16 centers were retrospectively evaluated for changes of P100 latencies and P100-N140 amplitudes. Rates of change in latencies (RCL) and amplitudes (RCA) over time were analyzed for each individual eye using linear regression and compared using generalized estimating equation models. The rates of change in the absence of optic neuritis (ON) for minimal VEP intervals of greater than or equal to 3 months between baseline and last follow-up were +1.951 ms/y (n = 101 eyes; SD = 6.274; p = 0.012) for the P100 latencies and -2.149 µV/y (n = 64 eyes; SD = 5.013; p = 0.005) for the P100-N140 amplitudes. For minimal VEP intervals of greater than or equal to 12 months, the RCL was +1.768 ms/y (n = 59 eyes; SD = 4.558; p = 0.024) and the RCA was -0.527 µV/y (n = 44 eyes; SD = 2.123; p = 0.111). The history of a previous ON of greater than 6 months before baseline VEP had no influence on RCL and RCA. ONs during the observational period led to mean RCL and RCA of +11.689 ms/y (n = 16 eyes; SD = 17.593; p = 0.003) and -1.238 µV/y (n = 11 eyes; SD = 3.708; p = 0.308), respectively. The authors concluded that this first longitudinal VEP study of patients with NMOSD provided evidence of progressive VEP latency delay occurring independently of acute ON. These researchers stated that prospective longitudinal studies are needed to corroborate these findings and help to interpret the clinical relevance.Auditory Evoked Potential for Evaluation of Hearing and Language Deficits in Survivors of Extracorporeal Membrane Oxygenation
Lott et al (1990) examined clinical and neurophysiologic measures in 10 children aged 4 to 9 years after neonatal extracorporeal membrane oxygenation (ECMO). Electroencephalograms (EEG) did not correlate with clinical or other neurophysiologic measures of inter-hemispheric asymmetry. By ultrasound (US) imaging, the right internal carotid artery velocity was approximately 62 % of that on the left, and right internal carotid flow was reduced by 74 % (p ≤ 0.01), whereas an age-matched control group showed no differences. A decrease in the amplitude of the long-latency AEP and SSEP was noted over the right hemisphere after left-sided stimulation compared with the left hemispheric potentials after right-sided stimulation (p ≤ 0.005). No significant differences in hemispheric symmetry were noted in the amplitudes for wave V of the auditory brain-stem response (ABSR) or in the P30 component of the middle-latency AEPs. Likewise, latency measures of the evoked potentials were symmetric. The authors concluded that neonatal ECMO was associated with long-lasting decreased right internal carotid blood flow with compensatory increased flow through the left carotid system; and there was a consistent reduction in the amplitude of right hemispheric long-latency evoked potentials. These latter findings may reflect re-directed cerebral blood flow (CBF) patterns after ECMO.
Desai et al (1997) examined the sensitivity and specificity of neonatal BAEP as markers for subsequent hearing impairment and for developmental problems found later in infancy and childhood. BAEP studies were performed before discharge in infants treated with ECMO, and 2 specific abnormalities were analyzed: elevated threshold and delayed central auditory conduction. Behavioral audiometry was repeated during periodic follow-up until reliable responses were obtained for all frequencies, and standardized developmental testing was also conducted. The sensitivity and specificity of an elevated threshold on the neonatal BAEP for detecting subsequent hearing loss, and the relationship of any neonatal BAEP abnormality to language or developmental disorders in infancy, were calculated. Test results for 46 ECMO-treated infants (57.5 %) were normal, and those for 34 infants (42.5 %) were abnormal, with either elevated wave V threshold, prolonged wave I-V interval, or both on neonatal BAEP recordings. Most significantly, 7 (58 %) of the 12 children with subsequent sensorineural hearing loss (SNHL) had left the hospital after showing normal results on threshold tests. There was no significant difference in the frequency of hearing loss between subjects with abnormal (5/21, or 24 %) and those with normal BAEP thresholds (7/59, or 12 %; Fisher Exact Test, p = 0.28). Thus, the sensitivity of neonatal BAEP testing for predicting subsequent hearing loss was only 42 %. Neonatal BAEP specificity for excluding subsequent hearing loss was 76 %. In contrast, on language development testing, 19 children demonstrated receptive language delay. Of these children, 12 (63 %) had abnormal neonatal BAEP recordings and 7 (37 %) had a normal BAEP threshold, normal central auditory conduction test results, or both (p = 0.04). The authors concluded that neonatal BAEP threshold recordings were of limited value for predicting subsequent hearing loss common in ECMO-treated survivors. However, an abnormal neonatal BAEP significantly increased the probability of finding a receptive language delay during early childhood, even in those with subsequently normal audiometry findings. Because neonatal ECMO is associated with a high risk of hearing and receptive language disorders, parents should be counseled that audiologic and developmental follow-up evaluations in surviving children are essential regardless of the results of neonatal BAEP testing.
Weichbold et al (2006) determined the percentage of children who have a post-natal permanent childhood hearing impairment (PCHI) and the percentage thereof who have risk indicators for a post-natal hearing loss. Data were drawn retrospectively from the clinical charts of children who had bilateral PCHI (greater than 40 dB hearing level, better ear, un-aided) and had undergone universal newborn hearing screening (UNHS) between 1995 and 2000 in various Austrian hospitals. A hearing loss was recognized as post-natal when a child passed UNHS but was later found to have a hearing impairment. The presence of risk indicators, as suggested by the Year 2000 Statement of the American Joint Committee on Infant Hearing (JCIH), was assessed by reviewing the children's clinical charts. Of a total of 105 children with bilateral PCHI, 23 (22 %) showed post-natal impairment. After correction of this number for under-ascertainment, post-natal impairment was estimated to account for 25 % of all bilateral PCHI at age of 9 years. Risk indicators were found in 17 children but did not fully correspond to those proposed by the JCIH. The risk factors found were a family history of hearing loss (n = 3 children), meningitis (n = 2), cranio-facial malformation (n = 2), persistent pulmonary hypertension (n = 1), congenital cytomegaly infection (n = 1), ECMO (n = 1), recurrent otitis media with effusion (n = 1), and, in addition to the JCIH list, ototoxic therapy (n = 5), and birth before 33rd gestational week (n = 2) (1 child had a combination of the last 2); 6 children showed no risk indicators for the post-natal hearing loss. The authors concluded that these findings suggested that approximately 25 % of bilateral childhood hearing loss was post-natal, which supported the leading role of UNHS in detecting PCHI. Provisions for also identifying post-natal cases nevertheless were justified. Because in some of these children no risk indicators were detectable and in others the hearing deterioration started after age 3 years, audiologic monitoring of at-risk children up to this age may not be sufficient. Additional methods, such as hearing screening at nursery schools or schools, were recommended.
Intraoperative Brainstem Neuromonitoring During Coil Embolization for the Treatment of Cerebral Aneurysms
Horowitz et al (2003) reported a case of intra-operative aneurysm rupture during endovascular therapy and documented the effects of rupture on cerebral transit times and neurophysiologic monitoring. A 42-year old man with Hunt and Hess grade 1, Fisher grade-3 subarachnoid hemorrhage (SAH) secondary to a 5-mm anterior communicating artery aneurysm underwent coil embolization. Endovascular therapy was complicated by intra-procedural aneurysm rupture. Changes in cerebral transit time and electroencephalography (EEG) along with SSEPs were documented as were improvement in these parameters following aneurysm obliteration and ventriculostomy placement. The patient awoke without deficit and was discharged 2 weeks later with a grossly normal examination. The authors concluded that early recognition of aneurysm rupture during coil embolization and prompt aneurysm obliteration and reduction in intra-cranial hypertension could lead to acceptable patient outcomes. These researchers stated that the use of neurophysiologic monitoring in the intubated patient could help the neurosurgeon determine the need for cerebrospinal fluid (CSF) drainage in such situations.
In a prospective study, Chen (2010) examined the efficacy of neurophysiological monitoring (NPM) techniques in the detection of ischemic changes that may be observed during endovascular treatment of cerebral aneurysms. A total of 63 patients underwent NPM during 1st-stage endovascular treatment of cerebral aneurysms. The endovascular procedures included coil embolization (26 patients), balloon-remodeling coiling (16 patients), stent-assisted coiling (10 patients), balloon-stent-assisted coiling (9 patients), and balloon test occlusion (2 patients). NPM included EEG, SSEP, and (BAEP, depending on the location of the aneurysm and its associated vascular territory. NPM changes were observed in 3 (4.8 %) patients and the procedures were altered immediately. No neurological changes were found post-endovascularly; 10 patients demonstrated abnormal angiographic findings without concurrent NPM changes, of which 5 patients developed visual disturbance or hemiparesis. The author concluded that NPM was a valuable monitoring tool for endovascular treatment of cerebral aneurysms. A combination of SSEP, EEG, BAEP or MEP may be particularly useful in situations in which neurological examination is not possible (such as when the patient is under general anesthesia) or when a patient's condition (such as obtunded SAH) precluded neurological examination. It should also be emphasized that the decision-making and changing of endovascular procedures would not only be based on NPM changes, but also the real-time abnormal angiographic findings. The author stated that BAEP monitoring detected functional changes along the auditory brain stem pathways; BAEP changes were most often caused by a brain stem insult, which could result from vertebrobasilar ischemia. However, ischemia in the cerebellum or posterior cerebral artery territories could still be missed. Other technical limitations include confounding anesthesia-related effects, which may mimic cerebral ischemia.
Ares et al (2018) noted that SSEP monitoring is used extensively for early detection and prevention of neurological complications in patients undergoing many different neurosurgical procedures. However, the predictive ability of SSEP monitoring during endovascular treatment of cerebral aneurysms is not well detailed. These researchers evaluated the performance of intra-operative SSEP in the prediction post-procedural neurological deficits (PPNDs) after coil embolization of intra-cranial aneurysms. This population-based cohort study included patients of greater than or equal to 18 years of age undergoing intra-cranial aneurysm embolization with concurrent SSEP monitoring between January 2006 and August 2012. The ability of SSEP to predict PPNDs was analyzed by multiple regression analyses and assessed by AUC. In a population of 888 patients, SSEP changes occurred in 8.6 % (n = 77); 28 patients (3.1 %) suffered PPNDs. A 50 % to 99 % loss in SSEP waveform was associated with a 20-fold increase in risk of PPND; a total loss of SSEP waveform, regardless of permanence, was associated with a greater than 200-fold risk of PPND. SSEPs displayed very good predictive ability for PPND, with AUC of 0.84 (95 % CI: 0.76 to 0.92). The authors concluded that this study supported the predictive ability of SSEPs for the detection of PPNDs. The magnitude and persistence of SSEP changes was clearly associated with the development of PPNDs. The utility of SSEP monitoring in detecting ischemia may provide an opportunity for neuro-interventionalists to respond to changes intra-operatively to mitigate the potential for PPNDs. These researchers stated that although further analysis of the clinical outcomes of patients who experienced changes in SSEP monitoring is needed, especially the long-term outcomes of patients with sub-total loss of signals, regular use of SSEP monitoring may allow the opportunity to respond to changes in monitoring in a way that minimizes both short- and long-term clinical deficits.
The authors stated that this study had several drawbacks. The limitations of such a retrospective analysis were fairly self-evident and well described in the literature. Subjective data, such as consistent documentation of neurological examinations prior to and after the procedure and self-reporting by the proceduralist for documentation of procedural complications, was always prone to bias; however, great care was taken to maximize fidelity of this data, and no gross mis-representations were noted during data collection. Furthermore, the focus on immediate PPNDs and lack of long-term follow-up may both over-state the gravity and permanence of these deficits and under-estimate the long-term differences between the sub-categorical SSEP changes.
Intraoperative Neuromonitoring During Cervical Lymphadenectomy (Modified Radical Neck Dissection)
Calo et al (2014) examined the ability of IONM in reducing the post-operative recurrent laryngeal nerve (RLN) palsy rate by a comparison between patients submitted to thyroidectomy with IONM and with routine identification alone. Between June 2007 and December 2012, a total of 2,034 consecutive patients underwent thyroidectomy by a single surgical team. These researchers compared patients who have had neuromonitoring and patients who have undergone surgery with nerve visualization alone. The number of patients in which neuromonitoring was not utilized (Group A) was 993, and the number of patients in which neuromonitoring was utilized (group B) was 1,041. In group A, 28 RLN injuries were observed (2.82 %), 21 (2.11 %) transient and 7 (0.7 %) permanent. In group B, 23 RLN injuries were observed (2.21 %), in 17 cases (1.63 %) transient and in 6 (0.58 %) permanent. Differences were not statistically significative. The authors concluded that visual nerve identification remains the gold standard of RLN management in thyroid surgery. Neuromonitoring helped to identify the nerve, in particular in difficult cases, but it did not decrease nerve injuries compared with visualization alone. Moreover, these researchers stated that future studies are needed to evaluate the benefit of IONM in thyroidectomy, especially in conditions in which the RLN is at high risk of injury.
Brauckhoff et al (2016) stated that continuous vagal IONM (CIONM) of the RLN may reduce the risk of RLN lesions during high-risk endocrine neck surgery such as operation for large goiter potentially requiring trans-sternal surgery, advanced thyroid cancer, and recurrence. A total of 55 consecutive patients (41 women, median age of 61 years, 87 nerves at risk) underwent high-risk endocrine neck surgery. CIONM was performed using the commercially available NIM-Response 3.0 nerve monitoring system with automatic periodic stimulation (APS) and matching endotracheal tube electrodes. All CIONM events (decreased amplitude/increased latency) were recorded; APS malfunction occurred on 3 sides (3 %). A total of 138 CIONM events were registered on 61 sides. Of 138, 47 (34 %) events were assessed as imminent (13 events) or potentially imminent (34 events) lesions, whereas 91 (66 %) were classified as artifacts. Loss of signal was observed in 7 patients. Actions to restore the CIONM baseline were undertaken in 58/138 (42 %) events with a median 60 s required per action; 4 RLN palsies (3 transient, 1 permanent) occurred: 1 in case of CIONM malfunction, 2 sudden without any significant previous CIONM event, and 1 without any CIONM event. The APS vagus electrode led to temporary damage to the vagus nerve in 2 patients. The authors concluded that CIONM using the APS system may be a useful tool in high-risk thyroid and parathyroid surgery in order to reduce the risk of RLN lesions. Moreover, these researchers noted that even though the technology has matured, a major development effort is needed to reduce EMG artifacts and improve the safety of CIONM systems. They also stated that randomized studies are needed in order to obtain reliable estimates of cost benefit.
The authors stated that this study had several drawbacks. First, the restricted number of patients undergoing high-risk surgery limited the number of relevant clinical events (loss of signal and RLN palsy). Second, due to the non-randomized study design, no final conclusion regarding the potential benefit of CIONM could be drawn. Third, even though classification of events as intrinsic versus artifactual was based on several objective parameters, it ultimately rested on the subjective evaluation by the surgeon. Therefore, these investigators could not exclude that some artifactual events were related to sub-clinical nerve damage and vice versa. Fourth, the protocol was not completely standardized (e.g., use of needle electrodes); however, this reflected clinical practice. Last, the results pertained to high-risk surgery and a specific device (APS) and could perhaps not be transferred to the systems by other manufacturers.
Yang et al (2017) stated that IONM has been a commonly used technology during thyroid surgery aimed at reducing the incidence of RLN palsy (RLNP), which is a severe complication and leads to significant impacts on a patient's life. In a systematic review and meta-analysis, these researchers provided a comprehensive assessment for potential benefits and disadvantage of IONM; they discussed RLNP rate, predictive power, CIONM, and emphasized on application during thyroid cancer surgeries. These investigators carried out a literature search in the following electronic databases: PubMed, Embase, and the Cochrane library from January 1, 2004 to July 30, 2016. After applying inclusion and exclusion criteria, a total of 24 studies, including 4 prospective, randomized trials, were selected. Heterogeneity of studies was checked by the Cochran Q test. Publication bias was assessed by funnel plots with Egger's linear regression test of asymmetry; OR was calculated by random effects model. A total of 9,203 patients and 17,203 nerves at risk (NAR) were included. Incidence of overall, transient, and persistent RLNP in IONM group were, respectively, 3.15 %, 1.82 %, and 0.67 %, whereas for the visual identification group, they were 4.37 %, 2.58 %, and 1.07 %. The summary OR of overall, transient, and persistent RLNP compared using IONM and ID were, respectively, 0.81 (95 % CI: 0.66 to 0.99), 0.76 (95 % CI: 0.61 to 0.94), and 0.78 (95 % CI: 0.55 to 1.09). The authors presented data showed benefits of reducing RLNP rate by using IONM, but without statistical significance for persistent RLNP rate. For patients with thyroid cancer who undergo total thyroidectomy, using IONM may improve the outcome by reducing amount of residual thyroid tissue. However, no benefits were found for thyroid re-operation; visual identification and careful dissection remain standard for this challenging procedure. Furthermore, the relative low positive predictive power indicated intermittent IONM (IIONM) may not be reliable; but CIONM was showed to be a more promising method, with prudent approach. These researchers stated that future studies may include larger patient number, and multi-center, prospective, randomized trials; and PPV of IONM should be improved through the establishment of standardized criteria for RLNP diagnosis.
Cirocchi et al (2019) stated that injuries to the recurrent inferior laryngeal nerve (RILN) remain one of the major post-operative complications after thyroid and parathyroid surgery. Damage to this nerve can result in a temporary or permanent palsy, which is associated with vocal cord paresis or paralysis. Visual identification of the RILN is a common procedure to prevent nerve injury during thyroid and parathyroid surgery. Recently, IONM has been introduced in order to facilitate the localization of the nerves and to prevent their injury during surgery; IONM allows nerve identification using an electrode, where, in order to measure the nerve response, the electric field is converted to an acoustic signal. In a Cochrane review, these researchers examined the effects of IONM versus visual nerve identification for the prevention of RILN injury in adults undergoing thyroid surgery. They searched CENTRAL, Medline, Embase, ICTRP Search Portal and ClinicalTrials.gov. The date of the last search of all data-bases was August 21, 2018. These investigators did not apply any language restrictions. They included RCTs comparing IONM nerve identification plus visual nerve identification versus visual nerve identification alone for prevention of RILN injury in adults undergoing thyroid surgery; 2 review authors independently screened titles and abstracts for relevance. One review author carried out screening for inclusion, data extraction and “risk of bias” assessment and a 2nd review author checked them. For dichotomous outcomes, these researchers calculated risk ratios (RRs) with 95 % CIs. For continuous outcomes, they calculated mean differences (MDs) with 95 % CIs; and assessed trials for certainty of the evidence using the GRADE instrument. A total of 5 RCTs with 1,558 participants (781 participants were randomly assigned to IONM and 777 to visual nerve identification only) met the inclusion criteria; 2 trials were performed in Poland and 1 trial each was performed in China, Korea and Turkey. Inclusion and exclusion criteria differed among trials: previous thyroid or parathyroid surgery was an exclusion criterion in 3 trials. In contrast, this was a specific inclusion criterion in another trial. Three trials had central neck compartment dissection or lateral neck dissection and Graves' disease as exclusion criteria. The mean duration of follow-up ranged from 6 to 12 months. The mean age of participants ranged between 41.7 and 51.9 years. There was no firm evidence of an advantage or disadvantage comparing IONM with visual nerve identification only for permanent RILN palsy (RR 0.77, 95 % CI: 0.33 to 1.77; p = 0.54; 4 trials; 2,895 nerves at risk; very low-certainty evidence) or transient RILN palsy (RR 0.62, 95 % CI: 0.35 to 1.08; p = 0.09; 4 trials; 2,895 nerves at risk; very low-certainty evidence). None of the trials reported health-related quality of life (HR-QOL). Transient hypoparathyroidism as an adverse event (AE) was not substantially different between intervention and comparator groups (RR 1.25; 95 % CI: 0.45 to 3.47; p = 0.66; 2 trials; 286 participants; very low-certainty evidence). Operative time was comparable between IONM and visual nerve monitoring alone (MD 5.5 mins, 95 % CI: -0.7 to 11.8; p = 0.08; 3 trials; 1,251 participants; very low-certainty evidence); 3 of 5 included trials provided data on all-cause mortality: no deaths were reported. None of the trials reported socioeconomic effects. The evidence reported in this review was mostly of very low certainty, particularly because of risk of bias, a high degree of imprecision due to wide CIs and substantial between-study heterogeneity. The authors concluded that the findings from this systematic review and meta-analysis indicated that there is currently no conclusive evidence for the superiority or inferiority of IONM over visual nerve identification only on any of the outcomes measured. These researchers stated that well-designed RCTs with a larger number of participants and longer follow-up, employing the latest IONM technology and applying new surgical techniques are needed.
Stankovic et al (2020) noted that although the history of IONM dates back to the 19th century, the method did not evolve further than the mere differentiation of nerves until recently. Only the development of CIONM has allowed for non-stop analysis of excitation amplitude and latency during surgical procedures, which is nowadays integrated into the software of almost all commercially available neuromonitoring devices. The objective of CIONM is real-time monitoring of nerve status in order to recognize and prevent impending nerve injury and predict post-operative nerve function. Despite some drawbacks such as false-positive/negative alarms, technical artefacts, and rare AEs, CIONM remains a good instrument which is still under development. Active (aCIONM) and passive (pCIONM) methods of CIONM were described in the literature. The main fields of CIONM implementation are currently thyroid surgery (in which the vagal nerve is continuously stimulated) and surgery to the cerebello-pontine angle (in which the facial nerve is either continuously stimulated or the discharge signal of the nerve is analyzed via pCIONM). In the latter surgery, continuous monitoring of the cochlear nerve is also established. The authors provided the following conclusions:
- Continuous IONM is a new evolving instrument destined to help surgeons in performing surgical maneuvers in close proximity to neural structures.
- It cannot and does not replace good operative technique and patency; however, it does provide reliable and safe assistance.
- The safety of active CIONM (aCIONM) has been demonstrated in animal and human studies.
- The field appears to be open for future studies, especially in surgery of the parotid gland where to-date neither aCIONM nor pCIONM has been applied.
Furthermore, UpToDate reviews on “Neck dissection for differentiated thyroid cancer” (Sippel, 2020) and “Treatment of locoregionally advanced head and neck cancer: The oropharynx” (Worden et al, 2020) do not mention intraoperative neuromonitoring as a management option.
Intraoperative Neuromonitoring During Craniotomy Repair of Cerebrospinal Fluid Leak
Feng et al (2014) noted that CSF leak may occur during the preparation of trajectory of thoracic pedicle screws in scoliosis surgery. The strategy for management of such situation is controversial. There is limited literature regarding the CSF leak and concomitant neuromonitoring change. In a retrospective study, these researchers analyzed CSF leak during the thoracic pedicle screw fixation in spinal deformities, the relative IONM changes and the strategy for management. A total of 695 patients with spinal deformity subjected to correction by posterior instrumentation using thoracic pedicle screw fixation from 2008 January to 2010 December and followed-up for more than 2 years were retrospectively analyzed for CSF leak during pedicle screw placement and the concomitant neuromonitoring changes. The cases with CSF leak and with complete information regarding neuromonitoring were reviewed. A total of 7,284 thoracic pedicle screws were inserted in the thoracic level (10.4 screws/patient). All the procedures were carried out under the IONM. There were 8 cases of CSF leak with the rate of 0.11 % during the screw trajectory preparation; 7 of the screws located at the concave side; 5 cases presented with concomitant positive IONM changes. The holes were sealed for 3 of them, and patients presented with reversible monitoring changes and intact neurological function. Negligence of the CSF leak and screw insertion caused the deterioration of neuromonitoring even neurological deficit that needed revision surgery; 3 cases presented without IONM changes and woke-up without neurological deficit. The authors concluded that the factors impacting the safety of screw placement for CSF leak included screw position, segment of vertebra, and concomitant neuromonitoring changes. Commonly, it was unnecessary to repair the dural tear and sealing the pedicle hole with bone wax for the case with reversible neuromonitoring changes was all that needed. A lateral entry point to the initial one could be used and to continue the screw placement when neuromonitoring demonstrated reversible positive changes. Level of Evidence = IV.
Silverstein et al (2018) stated that transcranial MEP (TCMEP) and direct cortical MEP (DCMEP) paradigms have historically been used contemporaneously or independently for supratentorial craniotomies. DCMEP provides focal stimulation to the cortical surface, whereas TCMEP stimulation is more variable and may be activating structures deeper than those at risk during a supratentorial craniotomy. These researchers presented the case of a 65-year old woman who underwent a supratentorial craniotomy for the clipping of a right-sided unruptured middle cerebral artery (MCA) aneurysm. DCMEP recordings of the upper extremity (UE) degraded after the parent vessel was temporarily occluded with a clip. The recordings returned once the clip was released. The DCMEP lower extremity (LE) recordings did not deviate from their established baseline. TCMEP recordings (UEs and LEs) also did not deviate from their established baselines. The permanent clip was placed without incident, and the patient awoke neurologically intact. This case study demonstrated the specificity and sensitivity of DCMEP versus TCMEP. DCMEP activated the corticospinal tract more superficially; thus, it was evident by the loss of the UE DCMEPs without the loss of LE DCMEPs that the temporary vessel occlusion caused an ischemic event focal to the cortical area perfused by the MCA. This ischemic event was not detected by TCMEP. The authors concluded that TCMEP and DCMEP are part of the neurophysiologist’s and neurosurgeon’s armamentarium and should be used accordingly. DCMEPs are shown to be more specific and more sensitive than TCMEPs in supratentorial craniotomy and should be employed when feasible. TCMEPs should not be discarded or discontinued, as they do have benefits in cranial surgery. For example, the establishment of pre-incision baseline data can be used as a pilot to what should be expected from DC stimulation. However, the expectations of their utility as an indicator of the cortical function should be managed, and if only using TCMEP, it should be understood that the risk of a false-negative occurring is increased, even if the neurophysiologist has controlled for the “crossover” response. This was a single-case study that examined the use of MEP.
Beck et al (2019) stated that spinal CSF leaks are the cause of spontaneous intracranial hypotension (SIH). These investigators proposed a surgical strategy, stratified according to anatomic location of the leak, for sealing all CSF leaks around the 360° circumference of the dura through a single tailored posterior approach. All consecutive SIH patients undergoing spinal surgery were included. The anatomic site of the leak was localized. These researchers used a tailored hemi-laminotomy and IONM for all cases. Neurological status was examined before and up to 90 d after surgery. A total of 47 SIH patients had an identified CSF leak between the levels C6 and L1. Leaks, anterior to the spinal cord, were approached by a transdural trajectory (n = 28). Leaks lateral to the spinal cord by a direct extradural trajectory (n = 17) and foraminal leaks by a foraminal microsurgical trajectory (n = 2). The transdural trajectory necessitated cutting the dentate ligament accompanied by elevation and rotation of the spinal cord under continuous neuromonitoring (spinal cord release maneuver, SCRM); 4 patients had transient deficits, none had permanent neurological deficits. These researchers proposed an anatomic classification of CSF leaks into I ventral (77 %, anterior dural sac), II lateral (19 %, including nerve root exit, lateral, and dorsal dural sac), and III foraminal (4 %). The authors concluded that safe sealing (with IONM) of all CSF leaks around the 360° surface of the dura was feasible through a single posterior approach. The exact surgical trajectory was selected according to the anatomic category of the leak.
Intraoperative Neuromonitoring During Shoulder Surgery
In a prospective, cohort study, Esmail et al (2005) examined the ability of a novel IONM method used to locate the axillary nerve, predict relative capsule thickness, and identify impending injury to the axillary nerve during arthroscopic thermal capsulorrhaphy of the shoulder. A total of 20 consecutive patients with glenohumeral instability were monitored prospectively during arthroscopic shoulder surgery. Axillary nerve mapping and relative capsule thickness estimates were recorded before the stabilization portion of the procedure. During labral repair and/or thermal capsulorrhaphy, continuous and spontaneous EMG recorded nerve activity. Furthermore, trans-spinal MEPs of the 4th and 5th cervical roots and brachial plexus electrical stimulation, provided real-time information regarding nerve integrity. Axillary nerve mapping and relative capsule thickness were recorded in all patients. Continuous axillary nerve monitoring was successfully performed in all patients; 11 of the 20 patients underwent thermal capsulorrhaphy alone or in combination with arthroscopic labral repair; 9 patients underwent arthroscopic labral repair alone. In 4 of the 11 patients who underwent thermal capsulorrhaphy, excessive spontaneous neurotonic EMG activity was noted, thereby altering the pattern of heat application by the surgeon. In 1 of these 4 patients, a small increase in the motor latency was noted after the procedure but no clinical deficit was observed. There were no neuromonitoring or clinical neurologic changes observed in the labral repair group without thermal application. At last follow-up, no patient in either group had any clinical evidence of nerve injury or complications from neurophysiologic monitoring. The authors successfully evaluated the use of IONM to identify axillary nerve position, capsule thickness, and provide real-time identification of impending nerve injury and function during shoulder thermal capsulorrhaphy. The use of IONM altered the heat application technique in 4 of 11 patients and may have prevented nerve injury. These findings need to be validated by well-designed studies.
Parisien et al (2016) compared the incidence and pattern of potential nerve injuries between reverse shoulder (RSA) and total shoulder arthroplasty (TSA) using IONM. These researchers hypothesized that RSA has a greater risk of nerve injury than TSA due to arm lengthening. They reviewed 36 consecutive patients who underwent RSA (n = 12) or TSA (n = 24) with IONM. The number of nerve alerts was recorded for each stage of surgery. Neurologic function was assessed pre-operatively and post-operatively at routine follow-up visits. Predictive factors for increased intra-operative nerve alerts and clinically detectable neurologic deficits were determined. There were nearly 5 times as many post-reduction nerve alerts per patient in the RSA cohort compared with the TSA cohort (2.17 versus 0.46). There were 17 unresolved nerve alerts post-operatively, with only 2 clinically detectable nerve injuries, which fully resolved by 6 months post-operatively. A pre-operative decrease in active forward flexion and the diagnosis of rotator cuff arthropathy were independent predictors of intra-operative nerve alerts. The authors concluded that RSA had a higher incidence of intra-operative nerve alerts than TSA during the post-reduction stage due to arm lengthening. Decreased pre-operative active forward flexion and the diagnosis of rotator cuff arthropathy were predictors of more nerve alerts. Moreover, these investigators stated that the clinical utility of routine IONM remained in question given the high level of nerve alerts and lack of persistent post-operative neurologic deficits.
In a case-series study, Shinagawa et al (2019) examined the risk of nerve injury with IONM during reverse total shoulder arthroplasty. This study included 15 shoulders of 15 patients (11 females and 4 males) who underwent RSA. The mean age of the subjects was 74.8 ± 4.4 years; 9 shoulders had cuff tear arthropathy, 4 had massive rotator cuff tears, 2 had osteoarthritis (OA), and 1 had RA. The SSEPs of the median nerve, transcranial MEPs, and free-EMGs from 6 upper-extremity muscles were measured intra-operatively. These researchers defined a nerve alert as 50 % amplitude attenuation or 10 % latency prolongation of the SSEPs and transcranial MEPs and sustained neurotonic discharge on free-EMG. A total of 31 alerts were recorded in 11 patients. The axillary nerve was associated with 17 alerts; 11 alerts occurred during the glenoid procedure and 5 alerts occurred during the humeral procedure; 1 patient who did not recover from the alert of the axillary nerve had clinically incomplete paralysis of the deltoid muscle. The authors concluded that the findings of this study suggested that the axillary nerve was the nerve most frequently exposed to the risk of injury, especially during glenoid and humeral implantation. Level of Evidence = IV.
Intraoperative Neuromonitoring During Temporal Artery to Middle Cerebral Artery Bypass in Patients with Moyamoya Disease
Chen et al (1989) described the findings of 20 Japanese children with Moyamoya disease who were investigated by examining the multi-modality evoked potentials (BAEP, FVEP and SSEP). BAEPs were abnormally prolonged wave I-III and wave III-V in each one (10 %). FVEPs were abnormal in 6 (30 %), included prolonged latencies, reduced amplitudes and poor waveform in one each, and delayed latencies as well as reduced amplitudes in 3. FVEPs significantly correlated with intellectual deterioration (p < 0.01). SSEPs were abnormal in 13 (65 %) significantly more frequent than BAEPs and FVEPs (p < 0.01); reduction of N20 in 7, delayed latencies of N13-N20 in 4, and both delayed latencies and reduced amplitudes of N20 in 2. The authors stated that these findings correlated well with the neurologic deficits, CT findings and EEG findings in this progressive cerebrovascular disease (Moyamoya disease) in children.
Intraoperative Neuromonitoring During Thoracotomy for Resection of Mediastinal Mass
Husain et al (2007) noted that conventional surgery on the descending thoracic aorta for aneurysm or dissection repair typically involves open thoracotomy and cross-clamping of the aorta. These procedures are associated with the potential for significant neurologic morbidity due to spinal cord ischemia. Endovascular stent graft (EVSG) repair of the descending thoracic aorta precludes the need for aortic cross-clamping and appeared to be associated with fewer neurologic complications. Several studies have demonstrated the utility of IONM during conventional aortic surgery; however, less information is available regarding IONM during EVSG repair.
Srivastava et al (2014) reported a rare case of benign thoracic dumb-bell tumor in the upper posterior mediastinum, which was successfully removed by posterolateral thoracotomy and foraminotomy, using intraoperative monitoring of spinal MEPs. This technique has many advantages including minimal morbidity and mortality, a single incision, 1-step complete resection with adequate exposure, spinal stabilization, avoidance of laminectomy, nerve root identification, and good predicted post-operative function.
Mikai et al (2019) reported the findings of a 33-year old woman who presented with a right cervical mass. Contrast computed tomography (CT) showed a multi-locular tumor with a clear border and heterogeneous contents including fat and calcification. The tumor was located adjacent to the vagus and recurrent nerves. To avoid injury of these nerves, these investigators resected the tumor through a median sternotomy and right cervical lateral incision; IONM was carried out using an NIM TriVantage EMG tube (Medtronic, Minneapolis, MN). After the surgery, no neuropathy such as hoarseness was recognized. Pathological diagnosis showed a benign mature teratoma. The authors concluded that IONM was useful for superior mediastinal surgery around the vagus and recurrent nerves.
An UpToDate review on “Overview of open surgical repair of the thoracic aorta” (Burke, 2020) states that “For patients at high risk for spinal cord ischemia (i.e., extent I and II disease, e.g., descending thoracic aortic aneurysm and thoracoabdominal aortic aneurysm repair), cerebrospinal fluid drainage and perioperative monitoring of spinal perfusion pressure (mean arterial pressure - spinal pressure of greater than 80 mmHg) and spinal cord function are recommended. In our protocol, we maintain intrathecal pressure ≤ 10 mmHg. Intraoperative motor or somatosensory evoked potential monitoring can also be used to detect early spinal cord ischemia, which may help guide therapy. It is reasonable to base the decision to use neurophysiologic monitoring on individual patient needs, institutional resources, the urgency of the procedure, and the surgical and perfusion techniques to be used during open thoracic aortic repair”.
Intraoperative Neuromonitoring During Zenkers Diverticulectomy
Ataka et al (2020) noted that Killian-Jamieson diverticulum is a rare pharyngo-esophageal diverticulum. The risk of intra-operative injury of the recurrent laryngeal nerve (RLN) is high during surgical resection of Killian-Jamieson diverticulum because the RLN usually runs next to the base of the diverticulum. These researchers presented a case of Killian-Jamieson diverticulum that was safely resected with effective use of an IONM system with a hand-held stimulating probe to prevent RLN injury. This case entailed a 69-year old man who complained of dysphagia, and was diagnosed with Killian-Jamieson diverticulum and underwent open transcervical diverticulectomy. Because the anterior aspect of the diverticulum was expected to be close to the RLN, the accurate location of the RLN was checked during dissection by intermittent stimulation using a hand-held probe of the IONM system to avoid mechanical and thermal injury. The diverticulum was transected longitudinally using a linear stapler, and the staple line was buried using absorbable sutures from the distal end. During its closure, RLN was identified very close to the diverticulum stump by IONM, and the upper side of the stump was left unburied to avoid RLN injury. The post-operative course was uneventful and the patient was discharged on post-operative day 7. Post-operative evaluation showed no vocal cord paralysis. The authors concluded that IONM may be beneficial during open surgery for Killian-Jamieson diverticulum, which usually protrudes just lateral to the RLN. The finding of this single-case study needs to be validated by well-designed studies.
Furthermore, an UpToDate review on “Zenker's diverticulum” (Schiff and van Delft, 2020) does not mention intraoperative nerve monitoring.
Ocular Vestibular Evoked Myogenic Potentials for Diagnosis of Myasthenia Gravis
De Meel et al (2020) validated the repetitive ocular vestibular evoked myogenic potentials (RoVEMP) test for diagnostic use in myasthenia gravis (MG) and examined its value in diagnostically challenging subgroups. The RoVEMP test was carried out in 92 patients with MG, 22 healthy controls, 33 patients with a neuromuscular disease other than MG (neuromuscular controls), 4 patients with Lambert-Eaton myasthenic syndrome, and 2 patients with congenital myasthenic syndrome. Mean decrement was significantly higher in patients with MG (28.4 % ± 32.2) than in healthy controls (3.2 % ± 13.9; p < 0.001) or neuromuscular controls (3.8 % ± 26.9; p < 0.001). With neuromuscular controls as reference, a cut-off of greater than or equal to 14.3 % resulted in a sensitivity of 67 % and a specificity of 82 %. The sensitivity of the RoVEMP test was 80 % in ocular MG and 63 % in generalized MG. The RoVEMP test was positive in 6 of 7 patients with sero-negative MG (SNMG) with isolated ocular weakness. Of 10 patients with SNMG with negative repetitive nerve stimulation (RNS) results, 73 % had an abnormal RoVEMP test . The magnitude of decrement was correlated with the time since the last intake of pyridostigmine (B = 5.40; p = 0.019). The authors concluded that the RoVEMP test is a new neurophysiologic test that, in contrast to RNS and single-fiber EMG, was able to measure neuromuscular transmission of extra-ocular muscles, which are the most affected muscles in MG. Especially in diagnostically challenging patients with negative antibody tests, negative RNS results, and isolated ocular muscle weakness, the RoVEMP test has a clear added value in supporting the diagnosis of MG. This study provided Class III evidence that RoVEMP distinguishes MG from other neuromuscular diseases.
The authors stated that drawbacks of this study included the single center of inclusion and this study population within a tertiary referral center that may not fully reflect the total MG population due to a referral bias. The control group of neuromuscular patients did not reflect the whole range of patients with diplopia due to a neuromuscular disease other than MG. However, these researchers included control patients with disorders that were previously reported to cause diagnostic confusion and delay due to similarities in presenting symptoms compared to OMG. Methodologic limitations of this trial included the fact that inter-rater reliability was not formally examined and the fact that researchers were not blinded to clinical status. These methodologic limitations were likely to have a minimal impact because the role of the investigator was limited to placing electrodes, encouraging the patient to relax, and placing the mini-shaker, but further studies on reliability will still be needed to prove this. All post-processing and decrement calculation were fully automated by a Matlab script. Another limitation was the (current) impossibility of including patients with excessive blinking in response to the vibrations. In this study, these investigators have excluded 3 % of the subjects due to this problem. By further optimizing stimulus parameters, altering the procedure of testing in patients with excessive blinking (e.g., lowering the stimulus intensity), and optimizing postprocessing, these researchers hope to increase diagnostic yield in future studies. The RoVEMP results of 1 patient with MG, 2 healthy controls, and 2 neuromuscular controls were not analyzable due to excessive blink artifacts and were excluded.
Short-Latency Somatosensory Evoked Potential (SSEP) Study for Evaluation of Movement Disorders
Pratt et al (1979) recorded short-latency SSEP by mechanical stimulation by surface electrodes over the digital nerves in the index finger, the median nerve at the wrist, the median nerve near the axilla, the brachial plexus, the cervical cord at CII, and the scalp overlying the somatosensory cortex. Nerve conduction velocities (NCVs) varied inversely with age and ranged from 43 to 68 m/sec. Mechanically evoked potentials recorded from the electrodes overlying the digital nerves were an artifact of the finger movement. All other electrode configurations recorded potentials comparable to those evoked by electrical stimulation of nerves. The authors concluded that these mechanically evoked potentials could prove useful in the evaluation of clinical disorders of somatosensory function from receptor to cortex in man.
UpToDate reviews on “Hyperkinetic movement disorders in children” (Jankovic, 2020), and “Functional movement disorders” (Miyasaki, 2020) do not mention short-latency SSEP as a management option.
Cervical Vestibular Evoked Myogenic Potential (cVEMP) for the Evaluation of Vertigo
Lee et al (2017) noted that vestibular-evoked myogenic potentials (VEMPs) can be abnormal in patients with idiopathic recurrent spontaneous vertigo. These researchers examined if abnormal cervical VEMPs (cVEMPs) can predict evolution of isolated recurrent vertigo into Meniere's disease (MD). They had followed-up 146 patients with isolated recurrent vertigo and an evaluation of cVEMPs for 0 to 142 months [median of 6, inter-quartile range (IQR) = 0 to 29] at the Dizziness Clinic of Seoul National University Bundang Hospital from June 2003 to May 2014. These investigators defined the variables associated with a progression into MD and calculated cumulative progression rates. Among the 94 patients with recurrent vertigo and abnormal cVEMPs, 18 (18/94, 19 %) showed an evolution into MD while only 2 of the 50 (4 %) patients with normal cVEMPs evolved into MD during the follow-up (p = 0.01). The interval between onset of vertigo and development of cochlear symptoms ranged from 1 month to 13.6 years (median of 3 years, IQR = 0.5 to 4.5 years). Overall, pure tone audiometry (PTA) threshold at 0.25-kHz [hazard ratio (HR) = 1.1, 95 % confidence interval (CI): 1.0 to 1.2] and abnormalities of cVEMPs (HR = 5.6, 95 % CI: 1.3 to 25.5) were found to be significantly associated with a later conversion into MD. The cumulative progression rate was 12 % (95 % CI: 5 to 18) at 1 year, 18 % (8 to 26) at 2 years, and 22 % (11 to 32) at 3 years. The authors concluded that abnormal cVEMPs may be an indicator for evolution of isolated recurrent vertigo into MD. Patients with isolated recurrent vertigo may be better managed conforming to MD when cVEMPs are abnormal.
Semmanaselvan et al (2019) stated that VEMP abnormalities in individuals with benign paroxysmal positional vertigo (BPPV) are often reported to be associated with utricle and saccule degeneration. These researchers evaluated the frequency of VEMP abnormalities using VEMPs in individuals with posterior canal BPPV after Epley's maneuver. A total of 36 individuals (36 ears) with definite posterior canal BPPV and 36 healthy controls were considered for the present study. All subjects underwent otoscopic examination, Dix-Hallpike maneuver to diagnose posterior canal BPPV. Further audiological evaluation including PTA was performed to rule out vestibular disorders associated with hearing loss. Epley's maneuver was performed on all individuals with BPPV by an experienced otorhinolaryngologist. Cervical and ocular VEMP were used to examine the saccule and utricle functions following Epley's maneuver . Cervical VEMP (cVEMP) and ocular VEMP (oVEMP) abnormalities were observed in 8/36 (22.22 %) and 18/36 (50 %) affected ears with BPPV, respectively. Cervical VEMP responses were reduced in amplitude among 1/36 (2.77 %) and absent in 7/36 (19.44 %) of affected ears with BPPV. Ocular VEMP responses were reduced in amplitude on 11/36 (30.55 %), followed by absent responses in 5/36 (13.88 %) ears with BPPV; 2 patients with posterior canal BPPV i.e., 4/64 (5.55 %) ears had bilateral absence of oVEMP responses. Two ears with BPPV 2/36 (5.55 %) had absence of both cVEMP and oVEMP responses in BPPV affected ear. T-test showed significant difference (p < 0.01) in the amplitude of oVEMP among posterior canal BPPV individuals when compared to cVEMP. The authors concluded that the findings of this study highlighted individuals with posterior canal BPPV may have otoconia dislodgement or macular degeneration of utricle, saccule, both utricle and saccule unilaterally, or bilaterally. These researchers stated that VEMP may be useful in evaluating degeneration of both otolith organs associated with BPPV.
Xu et al (2019) examined the diagnostic value of VEMP (cVEMP and oVEMP), caloric test, and cochlear electrogram (EcochG) in patients with Meniere's disease (MD) and non-MD. A total of 64 patients (64 ears) with unilateral MD were enrolled in the study group (MD group), and 127 cases (254 ears) of non-MD patients as non-MD group, including vertigo migraine in 40 cases, BPPV in 48 cases, benign recurrent vertigo in 13 cases, vestibular paroxysmia in 3 cases, vestibular neuritis in 5 cases and other undiagnosed vertigo in 18 cases. Both groups underwent cVEMP, oVEMP, caloric test and ECochG. Medcale software was used to draw ROC curve of ECochG and calculate the area under curve (AUC), Jordan index and optimal diagnostic cut-off points. The cut-off point was the point of -SP/AP, then the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of cVEMP, oVEMP, caloric test and ECochG in MD group and non-MD group were evaluated. The AUC of ECochG ROC curve was 0.74, the Jordan index was 0.47 and the cut-off point was 0.4. The sensitivity and specificity of cVEMP (62 % and 68 %), oVEMP (61 % and 53 %), and caloric test (53 % and 57 %) were all below ECochG (65 % and 78 %). The PPV of ECochG was the highest (61.9 %, the NPV of cVEMP was highest (87.5 %). The diagnostic accuracy of ECochG was highest (74 %), followed with cVEMP (67 %), oVEMP (55 %) and caloric test (56 %). The authors concluded that compared with the vestibular function tests, the sensitivity, specificity, diagnostic accuracy and NPV were all higher in ECochG, and the diagnostic benefit can be maximized when -SP/AP value greater than 0.4. Thus, the value of single vestibular function examination in the diagnosis of Meniere's disease is limited. The diagnosis of MD still requires a comprehensive evaluation in combination with medical history, audiological tests and vestibular function examinations.
Gunes et al (2020) noted that cVEMP measurements still do not have standard normative values in posterior canal BPPV. These researchers compared cVEMP recordings obtained with different stimuli applied in 2 different intensities in posterior canal BPPV patients. A total of 34 patients with unilateral posterior canal BPPV were included in the patient group. In cVEMP recordings obtained with different stimulus intensity [95 dB HL and 105 dB HL] and different stimuli [tone-burst cVEMP (T-cVEMP) and click cVEMP (C-cVEMP)]. When the C-cVEMP and T-cVEMP findings were compared in the patient group, differences were observed only in peak-to-peak p1-n1 amplitude values in the measurements performed with 95 dB stimulus; however, T-cVEMP measurements performed with 105-dB stimulus showed that both p1 and n1 latency values were longer and peak-to-peak p1-n1 amplitude values were higher than C-cVEMP measurements. The authors recommended using pure tone-burst stimulus for measurements with 105-dB HL in cVEMP evaluations they would perform in posterior BPPV patients. Both stimulants can be used when 95-dB HL stimuli is used.
Furthermore, an UpToDate review on “Evaluation of the patient with vertigo” (Furman and Barton, 2021) states that “cVEMPs are especially useful for detecting superior semicircular canal dehiscence syndrome, which will manifest as a cVEMP with a reduced threshold”.
Intra-Operative Neuromonitoring During Femur, Tibia/Fibula Osteotomy and Ankle Arthrodesis
Li et al (2018) noted that transcranial motor evoked potential (TcMEP) is widely used intra-operatively to monitor spinal cord and nerve root function. To the authors’ knowledge, there is no report regarding TcMEP signal loss purely caused by patient positioning during the spinal procedure. In a retrospective, case report, these investigators reported an intra-operative TcMEP signal loss of a patient with fixed sagittal imbalance posture along with mild hip contractures. A 57-year old man had fixed sagittal imbalance and flexed hip contractures. For a reconstruction surgery of T10 to the sacrum/ilium and L5 pedicle subtraction osteotomy (PSO), he was put in a prone position on a Jackson table. In order to accommodate his fixed hip flexion contracture, thigh pads were not used; and pillows were placed under his bilateral thighs for cushioning. TcMEPs were used to evaluate lumbar nerve root function. Ten minutes after incision, bilateral vastus medialis TcMEPs were lost during spine exposure whereas all other data remained normal at baseline. The bilateral lower extremities were re-positioned, with the knees flexed into a sling position to increase hip flexion. Five minutes after re-positioning, the bilateral vastus medialis TcMEPs gradually improved and maintained baseline amplitude during the remainder of the surgery. No muscle weakness was detected immediately after surgery. The patient was discharged 6 days post-operatively with markedly improved posture and alignment. The authors concluded that insufficient hip flexion in patients with fixed sagittal imbalance and hip flexion contractures may cause TcMEP signal changes in the quadriceps response. TcMEP monitoring of bilateral lower extremities is highly recommended for patients with sagittal imbalance and hip contractures, with consideration for lower extremity re-positioning when data degradation did not correlate with the actual spinal procedure being performed.
Furthermore, an UpToDate review on “Total joint replacement for severe rheumatoid arthritis” (Rinaldi, 2021) does not mention intra-operative neuromonitoring as a management tool.
Intra-Operative Neuromonitoring During Sacroiliac Joint Fusion
In a retrospective, case-series, single-center study, Woods et al (2014) documented the clinical utility of intra-operative neuromonitoring during minimally invasive surgical sacroiliac joint (SIJ) fusion for patients diagnosed with SIJ dysfunction (as a direct result of SIJ disruptions or degenerative sacroiliitis) and determined stimulated electromyography (EMG) thresholds reflective of favorable implant position. A medical chart review of consecutive patients treated with minimally invasive surgical SIJ fusion was undertaken at a single center. Baseline patient demographics and medical history, intra-operative EMG thresholds, and peri-operative adverse events (AEs) were collected after obtaining institutional review board (IRB) approval. A total of 111 implants were placed in 37 patients. Sensitivity of EMG was 80 % and specificity was 97 %; intra-operative neuromonitoring potentially avoided neurologic sequelae as a result of improper positioning in 7 % of implants. The authors concluded that the findings of this study suggested that intra-operative neuromonitoring may be a useful adjunct to minimally invasive surgical SIJ fusion in avoiding nerve injury during implant placement.
The authors stated that the drawbacks of this study included its small sample size (n = 37 patients), single surgeon experience, and absence of a control group. The small patient size was reflective of the number of patients available in the private practice office. All patients included in this study were followed post-operatively for a minimum of 3 months. The benefits of evaluating patients from a single center include a consistent diagnostic and therapeutic approach. Hopefully, in the near future, other surgeons will add to this body of knowledge and help validate the outcomes of this limited study.
Shamrock et al (2019) performed a systematic review of the existing literature to determine the safety of minimally invasive (MI)-SIJ fusion via the determination of the rate of procedural and device-related intra-operative and post-operative complications. All original studies with reported complication rates were included for analysis. Complications were defined as procedural if secondary to the MI surgery and device-related if caused by placement of the implant. Complication rates were reported using descriptive statistics. Random-effects meta-analysis was carried out for pre-operative and post-operative visual analog score (VAS) pain ratings and Oswestry Disability Index (ODI) scores. A total of 14 studies entailing 720 patients (499 females/221 males) with a mean follow-up of 22 months were included; 99 patients (13.75 %) underwent bilateral SI joint arthrodesis resulting in a total of 819 SI joints fused. There were 91 reported procedural-related complications (11.11 %) with the most common AE being surgical wound infection/drainage (n = 17); 25 AEs were attributed to be secondary to placement of the implant (3.05 %) with nerve root impingement (n = 13) being the most common. The revision rate was 2.56 %. MI-SIJ fusion reduced VAS scores from 82.42 (9 5% confidence interval [CI]: 79.34 to 85.51) to 29.03 (95 % CI: 25.05 to 33.01) and ODI scores from 57.44 (95 % CI: 54.73 to 60.14) to 29.42 (95 % CI: 20.62 to 38.21). The authors concluded that MI-SIJ fusion was a relatively safe procedure but is not without certain risks. These researchers stated that further investigation must be carried out to optimize the procedure's complication profile. Possible areas of improvement include pre-operative patient optimization, operative technique, and use of intra-operative real-time imaging. This review did not mention intra-operative neuromonitoring (electromyography, nerve conduction velocity study, motor evoked potential, and somatosensory evoked potential).
Intra-Operative SSEP During Open Reduction Internal Fixation (ORIF) of Acetabulum fracture
Calder et al (1994) examined the effectiveness of intra-operative sciatic nerve monitoring for 88 consecutive patients undergoing open reduction and internal fixation (ORIF) for acetabular fractures. Intervention outcomes and pre- and post-operative electrophysiologic status were compared to post-operative functional findings. Only 2 % of the patients demonstrated iatrogenic sciatic nerve palsies. Functional and evoked potential (Eps) findings were in agreement for 89 % of the patients with post-operative palsies, while 26 % of the functionally normal patients showed abnormal EPs. Intervention occurred in 55 surgeries; 80 % of interventions involved the peroneal nerve; 41 of the 55 patients who had interventions based on EP results showed recovery of responses to baseline. Of the 14 patients with incomplete intervention recovery, 11 showed impaired post-operative responses. Patients with pre-operative EP abnormalities did not show increased susceptibility to iatrogenic evoked potential changes.
In a retrospective, case-review study, Middlebrooks e al (1997) examined the incidence of sciatic nerve injury associated with the operative repair of acetabular fractures without SSEP monitoring. These researchers reviewed prospectively documented pre- and post-operative physical examinations. All the cases were reviewed of patients with ORIF of acetabular fractures who underwent posterior or extensile approaches (n = 129) performed by the 3 senior authors from January 1991 through March 1995. Intraoperative SSEP monitoring was not used during any of the procedures. The procedures included 65 Kocher-Langenbeck approaches, 34 combined Kocher-Langenbeck and ilio-femoral approaches, 4 extended ilio-femoral approaches, and 4 triradiate approaches; 1 case of iatrogenic nerve injury resulted in a sensory deficit. No patient suffered an exacerbation of a pre-existing nerve injury. The authors concluded that the findings of this study indicated that ORIF of acetabular fractures, using current techniques with visualization and protection of the sciatic nerve, can reduce the incidence of neurologic injury to a negligible level. There did not appear to be justification for the addition of SSEP or EMG modalities to the operative routine of experienced surgeons.
Arrington et al (2000) stated that monitoring of motor evoked potentials (MEP) and SSEP provides instantaneous intraoperative assessment of a patient's neurologic status. Monitoring of the sciatic nerve through MEP and SSEP can be used during ORIF of pelvic and acetabular fractures. These investigators carried out a review of 12 pelvic and acetabular fractures treated with ORIF and evaluated with a combination of intraoperative MEP and SSEP monitoring. Results revealed intraoperative MEP monitoring was 100 % sensitive and 100 % specific in predicting post-operative sciatic nerve deficits, whereas SSEP were not accurate in predicting post-operative sciatic nerve deficits. The authors concluded that combined monitoring of the sciatic nerve with MEP and SSEP is beneficial at predicting post-operative sciatic nerve deficits during ORIF of pelvic and acetabular fractures.
In a retrospective, non-randomized study, Haidukewych et al (2002) described their experience with iatrogenic nerve injuries and examined the efficacy of intraoperative monitoring in a large consecutive series of operatively treated acetabular fractures from January 1, 1992 through December 31, 1998. A total of 256 consecutive acetabular fractures were operatively treated at the authors’ institution; 140 unmonitored procedures and 112 monitored procedures were available for review. The decision to use monitoring was at the discretion of the treating surgeon. Intervention was ORIF of the acetabular fracture. Pre-operative and post-operative neurologic examinations, fracture type, use of traction, dislocation, operative approach, and complications were analyzed. Motor strength, sensation, the need for gait aids, orthoses, and extent of recovery were evaluated. Traumatic nerve palsies were present in 11 of 140 (7.9 %) unmonitored and 13 of 112 (11.6 %) monitored fractures (p = 0.314). There were 14 iatrogenic sciatic nerve palsies in 252 cases (5.6 %). There were 4 iatrogenic sciatic palsies (2.9 %) in the unmonitored group and 10 iatrogenic palsies (8.9 %) in the monitored group (p = 0.037). In the unmonitored group 1 of 81 Kocher-Langenbeck approaches (1.2 %), 2 of 52 ilio-inguinal (3.9 %), and 1 of 3 extended ilio-femoral approaches developed a sciatic palsy. In the monitored group 6 of 77 Kocher-Langenbeck approaches (7.8 %), 3 of 25 ilio-inguinal (12 %), and 1 of 6 combined approaches (16.7 %) developed a sciatic palsy. In 7 of the 10 iatrogenic palsies in the monitored group, the intraoperative monitoring was normal. A total of 76 patients were monitored with SSEP alone, and 9 had iatrogenic injuries (11.8 %); 36 patients were monitored with SSEP and EMG, and 1 had an iatrogenic injury (2.8 %) (p = 0.164). Clinical follow-up was available for 3 of the 4 patients with iatrogenic injuries in the unmonitored group, with a mean follow-up of 27 months (range of 8 to 60 months); 2 patients had full motor recovery at a mean of 6 months, and 1 had no recovery at 14 months. The authors concluded that the use of intraoperative monitoring did not decrease the rate of iatrogenic sciatic palsy. These researchers stated that further study involving larger prospective, randomized methodology appeared warranted. Sciatic nerve injury was more common in ilio-inguinal approaches in both groups, likely due to reduction techniques for the posterior column performed with the hip flexed, placing the sciatic nerve under tension.
Ocular Vestibular Evoked Myogenic Potential (oVEMP) for the Diagnosis of Benign Paroxysmal Positioning Vertigo
Xu et al (2016) stated that it is well-known that ocular vestibular evoked myogenic potentials (oVEMPs) predominantly reflect utricular function while cervical vestibular evoked myogenic potentials (cVEMPs) reflect saccular function. To-date, there are no published reports on the systemic evaluation of utricular and saccular function in benign paroxysmal positional vertigo (BPPV), nor are there any reports on the differences in VEMPs between patients with recurrent and non-recurrent BPPV. These researchers examined the difference in cervical and ocular (c/o)VEMPs between patients with BPPV and normal controls, as well as between patients with recurrent and non-recurrent BPPV. A total of 30 patients with posterior canal BPPV and 30 healthy subjects (as normal controls) were prospectively enrolled. cVEMP and oVEMP testing using 500 Hz tone-burst stimuli were performed on all. VEMP tests were repeated 3 times on each subject to ensure reliability and reproducibility of responses. VEMPs were defined as present or absent. Abnormal VEMP was defined by lack of VEMP response. In the control group, abnormal cVEMPs responses were detected in 6.67 % and abnormal oVEMPs responses were detected in 3.34 %. In BPPV patients (10 with recurrent BPPV, 20 with non-recurrent BPPV), abnormal cVEMPs responses were detected in 30 % and abnormal oVEMPs responses were detected in 56.7 %. More patients with BPPV showed abnormal responses in c/oVEMPs as compared to the control group (p < 0.05). oVEMPs was more often abnormal as compared to cVEMPs in BPPV patients (p < 0.05). There was no statistical difference between abnormal cVEMP responses in non-recurrent BPPV patients (25 %) and recurrent BPPV patients (40 %) (p > 0.05). Differences in abnormal oVEMP responses (non-recurrent BPPV, 40 %; recurrent BPPV, 90 %) were significant (p < 0.05). The authors concluded that an increased occurrence of abnormal c/oVEMP recordings appeared in BPPV patients, possibly as a result of degeneration of the otolith macula. oVEMPs were more often abnormal in BPPV patients as compared to cVEMPs, suggesting that utricular dysfunction may be more common than saccular dysfunction. Furthermore, oVEMP abnormalities in the recurrent BPPV group were significantly higher than those in the non-recurrent BPPV group. These researchers stated that assessment of c/oVEMPs in BPPV patients may therefore be of prognostic value in predicting likelihood of BPPV recurrence.
The authors stated that considering the controversy in the stability and repeatability of c/oVEMPs, they defined abnormal c/oVEMPs as absent responses in this study. As a result, these investigators did not analyze the latency and amplitude of the waves in c/oVEMPs. The main drawback of this study was the small number of BPPV patients (n = 30). As the incidence of BPPV is higher in the elderly and the average age of this study patients was under 60 years, there was a potential bias in the research. In future research, a larger sample size will be obtained such that quantitative analysis of otolith function in BPPV patients can be performed.
Semmanaselvan et al (2019) stated that VEMP abnormalities in individuals with BPPV are often reported to be associated with utricle and saccule degeneration. These investigators examined the frequency of VEMP abnormalities using VEMPs in individuals with posterior canal BPPV after Epley's maneuver. A total of 36 individuals (36 ears) with definite posterior canal BPPV and 36 healthy controls were considered for the present study. All of them underwent otoscopic examination, Dix-Hallpike maneuver to diagnose posterior canal BPPV. Further audiological evaluation including pure tone audiometry was performed to rule out vestibular disorders associated with hearing loss. Epley's maneuver was carried out on all individuals with BPPV by an experienced otorhinolaryngologist. cVEMP and oVEMP were used to examine the saccule and utricle functions following Epley's maneuver’ cVEMP and oVEMP abnormalities were observed in 8/36 (22.22 %) and 18/36 (50 %) affected ears with BPPV, respectively. Cervical VEMP responses were reduced in amplitude among 1/36 (2.77 %) and absent in 7/36 (19.44 %) of affected ears with BPPV; oVEMP responses were reduced in amplitude on 11/36 (30.55 %), followed by absent responses in 5/36 (13.88 %) ears with BPPV. Two patients with posterior canal BPPV i.e., 4/64 (5.55 %) ears had bilateral absence of oVEMP responses. Two ears with BPPV 2/36 (5.55 %) had absence of both cVEMP and oVEMP responses in BPPV affected ear. T-test showed significant difference (p < 0.01) in the amplitude of oVEMP among posterior canal BPPV individuals when compared to cVEMP. The authors concluded that this study highlighted individuals with posterior canal BPPV may have otoconia dislodgement or macular degeneration of utricle, saccule, both utricle and saccule unilaterally, or bilaterally. These researchers stated that VEMP may be useful in evaluating degeneration of both otolith organs associated with BPPV.
Oya et al (2019) noted that as the pathological cause of benign paroxysmal positional vertigo (BPPV), the dislocation or degeneration of otoconia in the utricle and saccule is suggested; and VEMP could reflect otolithic dysfunction due to these etiologies of BPPV. In a meta-analysis, these researchers examined the clinical significance of cVEMP and oVEMP in BPPV. Articles related to BPPV with data on cVEMP and oVEMP were collected. The following keywords were used to search PubMed and Scopus for English language articles: benign paroxysmal positional vertigo or BPPV and vestibular evoked myogenic potential or VEMP. The p13 latency in cVEMP and n1 latency in oVEMP were slightly but significantly prolonged in BPPV patients compared to control patients. AR in oVEMP of BPPV patients also showed higher value than that of control patients. However, the n23 latency and AR in cVEMP and p1 latency in oVEMP showed no significant difference between BPPV and control patients. Furthermore, latencies in VEMPs also showed no significant difference between an affected and a non-affected ear in BPPV patients. The authors concluded that the findings of this meta-analysis indicated that otolith dysfunction of BPPVs was detected by latencies in VEMPs, and AR in oVEMP more sensitively reflected the difference between affected and non-affected ears in BPPV patients. The otolith dysfunction of BPPV might be induced by the systemic condition. However, the differences of latencies between BPPV patients and control patients were too small to use VEMPs as a prognostic predictor.
Chen et al (2020) compared utricular dysfunction with saccular dysfunction in BPPV, based on oVEMP and (cVEMP, respectively. These researchers carried out a literature search examining utricular and saccular dysfunction in BPPV patients through June 2020 using oVEMP and cVEMP, respectively. The databases included PubMed, Embase, CENTRAL, CNKI, Wan Fang Data, and CBM. The literatures were limited to Chinese and English. Inclusion criteria and exclusion criteria were defined. These investigators adopted abnormal rate as the outcome. All statistical processes were performed by means of software Review Manager. Considering the air-conducted sound (ACS) and bone conducted vibration (BCV) may have different mechanisms, and 3 types of diagnostic criteria for abnormal VEMP were available, sub-group analysis was performed simultaneously according to the sound stimuli and the diagnostic criteria of abnormal VEMP. The authors retrieved 828 potentially relevant literatures, and finally 12 studies were included for meta-analysis of abnormal rate after duplication removal, titles and abstracts screening, and full-text reading. The abnormal rate of oVEMP was not significantly different from cVEMP (odds ratio [OR] = 1.59, 95 % confidence interval [CI]: 0.99 to 2.57). But the abnormal rate was obviously different between the subgroups adopting ACS oVEMP and BCV oVEMP. In studies adopting ACS oVEMP, the abnormal rate of oVEMP was higher than cVEMP (OR = 1.85, 95 % CI: 1.38 to 2.49). The abnormal rate of oVEMP was also higher than cVEMP when adopting asymmetry ratio (AR) and no response (NR) as diagnostic criteria (OR = 2.16, 95 % CI: 1.61 to 2.89). The authors concluded that this meta-analysis revealed that in oVEMP, the abnormal rate has been higher using ACS when compared to BCV, showing that BCV appeared to be more specific for the evaluation of utricular dysfunction. And in studies adopting ACS cVEMP and ACS oVEMP, the abnormal rate of oVEMP was higher than cVEMP. And the abnormal rate of oVEMP in BPPV patients was also higher than cVEMP with no heterogeneity if adopting AR and NR as diagnostic criteria. It was inferred that utricular dysfunction may be more predominant in BPPV compared with saccular dysfunction. These researchers stated that well-designed studies with large sample and normal control group and uniform parameters of VEMP testing are needed to further examine the otolith dysfunction of BPPV patients.
The authors stated that this review/meta-analysis had several drawbacks. First, a part of the studies adopted different stimulation modes, such as ACS and BCV. Even if they all adopted ACS, the intensity and frequency of acoustic stimuli may have a little difference. And only 1 study on BCV oVEMP was included in the meta-analysis. Second, the different diagnostic criteria for abnormal VEMP resulted in large heterogeneity. Third, the mean ages of BPPV individuals in the included articles were different from each other, and normal control group was absent.
Furthermore, an UpToDate review on “Benign paroxysmal positional vertigo” (Barton, 2021) does not mention vestibular evoked myogenic potential as a management option.
Olfactory Event‐Related Potential for the Evaluation of Long-Term COVID-19
Mazzatenta et al (2021) noted that COVID-19 is a public health emergency with cases increasing globally. Its clinical manifestations range from asymptomatic and acute respiratory disease to multi-organ dysfunction syndromes and effects of COVID-19 in the long-term. Interestingly, regardless of variant, all COVID-19 share impairment of the sense of smell and taste. These investigators reported, as far as they knew, the first comprehensive neurophysiological evaluation of the long-term effects of SARS-CoV-2 on the olfactory system with potential-related neurological damage. The case report concerned a military doctor, with a monitored health history, infected in April 2020 by the first wave of the epidemic expansion while on military duty in Codogno (Milan). In this subject, these researchers found the electrophysiological signal in the periphery, while its correlate was absent in the olfactory bulb region than in whole brain recordings. In agreement with this result was the lack of metabolic signs of brain activation under olfactory stimulation. Consequently, quantitative and qualitative diagnoses of anosmia were made by means of olfactometric tests. The authors strongly suggested a comprehensive series of olfactometric tests from the first sign of COVID-19 and subsequent patient assessments; and concluded that electrophysiological tests (olfactory event‐related potential and olfactory real‐time volatile organic compound test) and metabolic tests of olfactory function have made it possible to study the long-term effects and the establishment of neurological consequences.
Furthermore, an UpToDate review on “COVID-19: Evaluation and management of adults following acute viral illness” (Mikkelsen and Abramoff, 2021) states that “Olfactory/gustatory symptoms -- For patients who experienced a loss or decrease in their sense of smell or taste with acute COVID-19, we inquire about the degree of residual impairment and if their appetite or weight have been affected. Weight loss can be significant for some patients after critical illness for multifactorial reasons, and taste and smell impairment may contribute. In most cases, symptoms resolve slowly over several weeks and do not require intervention except for education regarding food and home safety. Patients with persistent gustatory and/or olfactory dysfunction may benefit from olfactory training, and self-guided programs are available online. If symptoms fail to resolve, further evaluation by an otolaryngologist may be needed, particularly in the setting of accompanying upper airway symptoms. Although not widely available, referral to a specialized taste and smell clinic may also be considered”. This review does not mention the sue of event‐related potentials as a management tool.
Pre-Operative SSEP of the Bilateral Tibial Somatosensory Pathways Prior To Scoliosis Surgery
In a prospective study, Shen et al (1996) reported the findings of 72 patients with the clinical diagnosis of adolescent idiopathic scoliosis (AIS) who underwent routine pre-operative magnetic resonance imaging (MRI) scans and neurologic consultations; 48 patients also had pre-operative somatosensory evoked potentials (SSEPs). All patients had normal neurologic examinations. Abnormal findings included 2 patients with Chiari type I malformation and 1 with a finding of a fatty collection in a vertebral body. In 4 cases, interpretation of the MRI was suspicious or equivocal, necessitating a computed tomography (CT) myelogram or other additional studies for clarification. Abnormal pre-operative SEP results were obtained in 3 patients, none of which proved significant. All surgical patients underwent instrumentation and fusion without incident. The authors concluded that the findings of this study indicated that routine preoperative SSEP is not necessary. Routine preoperative MRI is probably not indicated in AIS if the patient has a normal neurologic examination.
Hausmann et al (2003) reported the findings of a prospective study of spinal MRI, electrophysiological recordings, and neurological examinations of 100 patients admitted for surgery for AIS, which was conducted to evaluate the prevalence of structural and functional abnormalities within the spinal cord in patients with clinically normal neurologic condition. In all patients the clinical diagnosis and intact neurological condition was ascertained by a spinal orthopedic surgeon. Full-length spinal axis MRI studies (T1/T2 sequences) and SSEPs of the tibial nerves (tSSEPs) were pre-operatively examined by independent evaluators blinded to the patients' medical histories. Structural spinal cord abnormalities were found in 3 of 100 AIS patients on MRI. In 1 patient a Chiari malformation type 1 with an accompanying syringomyelia was diagnosed, which required a suboccipital decompression. In the other 2 patients small thoracic syringomyelias were diagnosed. Abnormalities of spinal cord function were detected in 68 % of the 100 patients: tSSEP latencies corrected for body height were increased in 56 % of the patients; pathological differences between tSSEPs on the left and right sides were present in 17 % (12 % in combination with a prolongation of the latency). The authors concluded that the findings of this study indicated that MRI and electrophysiological examinations are essential to evaluate spinal cord abnormalities that are clinically not detectable in AIS patients. Even in patients with intact neurologic condition and clinically typical right-curved thoracic scoliosis, the possibility of intra-spinal pathologies should be ruled out by MRI. It is especially important to detect structural pathologies like syringomyelia and Chiari malformation before proceeding with scoliosis surgery, as these conditions are associated with a higher neurological risk during scoliosis surgery. The electrophysiological recordings made in the present study, with the high number of pathological tSSEPs, are indicative of functional abnormalities with a sub-clinical involvement of the recorded neuronal pathways. The relevance of the latter findings is not yet clear, but pre-operative tSSEP examinations offer the possibility of evaluating alterations in spinal cord function that are undetectable by clinical examination.
Virk et al (2019) stated that intra-operative neuromonitoring is well established and widely used to assist in completing corrective surgery for AIS safely. The role of pre-operative measurement of SSEPs and/or transcranial magnetic stimulation (TMS) to determine if there is trans-spinal pathology, however, is unclear. These researchers examined if pre-operative SSEP and/or TMS measurement provided clinical benefit to patients with AIS. They carried out a review of medical charts between 2010 and 2012 for patients who underwent surgery for scoliosis; patients with diagnoses other than AIS were excluded. Patients with incomplete pre-operative or intra-operative data were also excluded. Relevant clinical information such as age, sex, number of levels fused, and major Cobb angle were recorded. Pre-operative neuromonitoring measurements and intra-operative neuromonitoring results were reviewed by an attending neurologist. Any instance in which an intra-operative surgical plan or neuromonitoring result interpretation was influenced by pre-operative results was recorded. Further imaging obtained based on pre-operative results was noted. Any acute neurologic complication such as paralysis was noted. A total of 81 patients met inclusion criteria (64 female, 17 male); average age was 15 years (± 1.92). Major Cobb angle at pre-operative evaluation averaged 57.5 degrees (± 10.81 degrees); 10 patients had abnormal pre-operative SSEP/TMS results. There were no changes in protocol during intra-operative neuromonitoring based upon pre-operative neuromonitoring findings. No additional imaging was needed for patients with abnormal pre-operative neuromonitoring results. There was no statistically significant difference in pre-operative Cobb angle between the group of patients with abnormal pre-operative neuromonitoring and those with normal baseline testing. The authors concluded that pre-operative SSEP/TMS measurement prior to corrective surgery for AIS has limited utility. There were no instances in which a patient's clinical course was improved by testing. These investigators recommended against routine use of preoperative SSEP/TMS testing for AIS patients requiring corrective surgery.
Furthermore, an UpToDate review on “Adolescent idiopathic scoliosis: Management and prognosis” (Scherl, 2021) states that “The preoperative evaluation for scoliosis surgery includes posteroanterior and lateral spinal radiographs and pulmonary function tests for patients with curves ≥ 60°. Lateral bending films for surgical planning may be obtained at the discretion of the surgeon”. It does not mention pre-operative SSEP.
Stimulus Evoked Response During Radical Prostatectomy
Reeves et al (2016) employed nerve conduction studies (NCS) to clarify the functional innervation of the male urethral rhabdo-sphincter (RS), especially to test the hypothesis that in some men, fibers of the neurovascular bundle supply the RS. These fibers may be at risk during radical prostatectomy (RP). In this trial, men undergoing robot-assisted RP for clinically localized prostate cancer (PCa) were included. Men with a history of pelvic surgery and/or radiation and/or trauma, obesity, or neurological diseases were excluded; NCS were carried out before and after prostate removal. The St. Mark's pudendal electrode was used for pudendal (control) stimulation. The ProPep Nerve-Monitoring System (ProPep Surgical, Austin, TX) was used to stimulate the neurovascular bundle at the level of the prostate base, mid, and apex. ProPep needle electrodes inserted into the RS were used to measure evoked compound motor action potential (cMAP)response. Results were only included if a valid pudendal control was elicited. A total of 17 men underwent investigation. Valid measurements were obtained after initial quality control in 7. In 2 cases, evidence of sphincteric activation was observed, providing evidence to support neurovascular bundle innervation of the RS. In the other 5 patients, no intra-pelvic nerve supply was demonstrated. The authors concluded that somatic nerve supply to the RS was variable. Direct intra-pelvic supply to the RS may exist in some men. This may be one explanation as to why some patients unexpectedly develop severe urinary incontinence (UI) post-operatively despite technically satisfactory surgery. Moreover, these researchers stated that further research is needed to validate these findings.
Furthermore, UpToDate reviews on “Radical prostatectomy for localized prostate cancer” (Klein, 2021), “Follow-up surveillance after definitive local treatment for prostate cancer” (Penson, 2021) and “Overview of approach to prostate cancer survivors” (Skolaru, 2021) do not mention stimulus evoked response as a management option.
Intraoperative Neuromuscular Junction Testing in Anoxic Brain Injury
An UpToDate review on “Hypoxic-ischemic brain injury in adults: Evaluation and prognosis” (Weinhouse and Young, 2022) does not mention neuromuscular junction testing as a management option.
Intraoperative Somatosensory Evoked Potential (SSEP) Monitoring During Hip Dysplasia and Labral Repair Surgery
Overzet et al (2018) noted that arthroscopic hip surgery is routinely carried out for the treatment of various hip disorders. Leg traction during labral tear repair, femoroplasty, and acetabuloplasty for hip stabilization can stretch the peripheral nerves. This may cause temporary or permanent nerve injury. In a retrospective study, these researchers examined the benefit of employing multi-modality IONM during hip surgical procedures. They conducted a review of 10 arthroscopic hip surgeries with neurophysiological monitoring at 1 medical center. Subjects consisted of 6 women and 4 men (mean age of 48.9 years). The procedures were equally divided into left and right-sided procedures. IONM setup included posterior tibial, peroneal, and femoral or saphenous nerve SSEPs, transcranial electrical MEP (TCeMEP), train of 4 (TOF), and EMG from the lower extremities. All subjects exhibited changes in IONM data during the surgical procedure. Changes in the latency and amplitude or loss of the lower SSEPs on the surgical side occurred in 36 % of the monitorable SSEPs. The surgeon instructed the team to reduce the leg lengthening by removing traction when changes were observed. The SSEPs exhibited a full recovery in 75 % of the affected lower extremity SSEPs. In the 2 instances of non-recovery, the SSEP responses remained increased in latency or decreased in amplitude at closing, but the waveform was intact. There were 5 instances of complete loss of the waveform (4 in the ipsilateral leg, and 1 in the contralateral leg) with recovery after traction was reduced. TCeMEP changes occurred in 53 % of the ipsilateral lower muscles monitored. Many of the TCeMEP changes were attributed to ischemia of the feet and could not be resolved intra-operatively. The authors concluded that multi-modality IONM could be a beneficial and protective tool during surgical procedures involving hip and acetabular areas. Early identification of changes in evoked potentials during hip arthroscopy surgeries could minimize post-operative neurological deficits due to peripheral nerve injury and leg ischemia.
Murena et al (2021) stated that sciatic nerve injury is an uncommon but potentially devastating complication in hip and pelvis surgery; IONM was employed since the 1970s in neurosurgery and spine surgery. To-date, IONM has gained popularity in other surgical specialties including orthopedic and trauma surgery. In a systematic review, these investigators examined the available evidence on the effectiveness of intra-operative monitoring of sciatic nerve during pelvic and hip surgery. Two reviewers independently identified studies by a systematic search of PubMed and Google Scholar from inception of database to January 10, 2021. Inclusion criteria entailed English written papers, use of any type of IONM during traumatic or elective pelvic and hip surgery, comparison of the outcomes between patients who underwent nerve monitoring and patient who underwent standard procedures, all study types including case reports. The present review was carried out in accordance with the 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The literature search produced 224 papers from PubMed and 594 from Google Scholar, with a total amount of 818 papers. The 2 reviewers excluded 683 studies by title or duplicates. Of the 135 remaining, 72 were excluded after reading the abstract, and 31 by reading the full text; therefore, 32 studies were finally included in the review. The authors concluded that the use of IONM during hip and pelvis surgery was debated. The review results were insufficient to support the routine use of IONM in hip and pelvis surgery. The different IONM techniques have peculiar advantages and disadvantages and differences in sensitivity and specificity without clear evidence of superiority for any. Results from different studies and different interventions were often in contrast. However, there is general agreement in recognizing a role for IONM to define the critical maneuvers, positions or pathologies that could lead to sciatic nerve intra-operative damage. Level of Evidence = II.
Intraoperative Somatosensory Evoked Potential (SSEP) Monitoring During Incision and Drainage of Paraspinal/Epidural Abscess of Cervical Spine
Abdelkader et al (2019) noted that monitoring of SSEPs serves as an early warning system to detect spinal cord injury and is correlated with post-operative sensory findings. It is an indirect indicator of motor function. These investigators examined the usefulness of intra-operative SSEPs monitoring as a stand-alone tool during spinal surgeries when MEPs are not available, to prevent and predict new post-operative neurologic deficits. MEPs were not used as the equipment needed to record them was not available at the time of this study. This trial included 50 patients, aged 14 to 67 years, undergoing extra-medullary manipulations, decompression of an epidural abscess or neoplasm, removal of intra-medullary tumor, or arterio-venous malformation (AVM) or spine correction procedures. SSEPs were analyzed for latency and peak-to-peak amplitude. Critical SSEP changes were defined as a 50 % decrease in amplitude or a 10 % increase in latency. SSEPs had an overall sensitivity of 81.8 %, a specificity of 100 %, a PPV of 100 %, and a NPV of 91.3 %. The authors concluded that intra-operative SSEPs have proven to be highly sensitive and specific for iatrogenic injury, mechanical stress caused by cord traction/compression, dural traction, lowered systemic blood pressure (SBP), and cord hypothermia. The reversibility of intra-operative SSEP changes showed a highly significant relation to the number of cases with new post-operative deficits as well as type and site of pathologic study (p = 0.00, p = 0.01, and p = 0.00, respectively) but not with the level of pathologic study (p = 0.49).
Reddy et al (2021) stated that cervical decompression and fusion surgery remains a mainstay of treatment for a variety of cervical pathologies. Potential intra-operative injury to the spinal cord and nerve roots poses non-trivial risk for consequent post-operative neurologic deficits. Although neuromonitoring with intra-operative SSEPs is often used in cervical spine surgery, its therapeutic value remains controversial. These researchers examined if significant SSEP changes could predict post-operative neurologic complications in cervical spine surgery. A subgroup analysis was carried out to compare the predictive power of SSEP changes in both anterior and posterior approaches. This study was a meta-analysis of the literature from PubMed, Web of Science, and Embase to identify prospective/retrospective studies with outcomes of patients who underwent cervical spine surgeries with intra-operative SSEP monitoring. The total cohort consisted of 7,747 patients who underwent cervical spine surgery with intra-operative SSEP monitoring. Inclusion criteria for study selection were as follows: prospective or retrospective cohort studies; studies conducted in patients undergoing elective cervical spine surgery not due to aneurysm, tumor, or trauma with intra-operative SSEP monitoring; studies that reported post-operative neurologic outcomes; studies conducted with a sample size 20 or more patients; studies with only adult patients 18 years of age or older; studies published in English; and studies inclusive of an abstract. The sensitivity, specificity, diagnostic odds ratio (DOR), and likelihood ratios of overall SSEP changes, reversible SSEP changes, irreversible SSEP changes, and SSEP loss for predicting post-operative neurological deficit were calculated. The total rate of post-operative neurological deficits was 2.50 % (194/7,747) and the total rate of SSEP changes was 7.36 % (570/7,747). The incidence of post-operative neurological deficit in patients with intra-operative SSEP changes was 16.49 % (94/570) while only 1.39 % (100/7,177) in patients without. All significant intra-operative SSEP changes had a sensitivity of 46.0 % and specificity of 96.7 % with a DOR of 27.32. Reversible and irreversible SSEP changes had sensitivities of 17.7 % and 37.1 % and specificities of 97.5 % and 99.5 %, respectively. The DORs for reversible and irreversible SSEP changes were 9.01 and 167.90, respectively. SSEP loss had a DOR of 51.39, sensitivity of 17.3 % and specificity 99.6 %. In anterior procedures, SSEP changes had a DOR of 9.60, sensitivity of 34.2 %, and specificity of 94.7 %. In posterior procedures, SSEP changes had a DOR of 13.27, sensitivity of 42.6 %, and specificity of 94.0 %. The authors concluded that SSEP monitoring was highly specific but weakly sensitive for post-operative neurological deficit following cervical spine surgery. The analysis found that patients with new post-operative neurological deficits were nearly 27 times more likely to have had significant intra-operative SSEP change. Loss of SSEP signals and irreversible SSEP changes appeared to indicate a much higher risk of injury than reversible SSEP changes. These investigators stated that SSEPs could likely be used during cervical spine surgeries to accurately predict the risk of post-operative neurologic deficits.
Motor Evoked Potential Monitoring for Peripheral Nerve Ablation
A position statement on “Intraoperative motor evoked potential monitoring” by the American Society of Neurophysiological Monitoring (Macdonald et al, 2013) did not mention peripheral nerve ablation as an indication of MEP monitoring.
Appendix
Documentation Requirements
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All medical necessity criteria must be clearly documented in the member's medical record and made available upon request.
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The member's medical record must contain documentation that fully supports the medical necessity for evoked potential studies. This documentation includes, but is not limited to, relevant medical history, physical examination, the anatomic location of the planned surgical procedure, the rationale for the location and modalities to be monitored, and results of pertinent diagnostic tests or procedures.
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For the BAERs, the member’s medical record should document the otologic exam describing both ear canals and tympanic membranes, as well as a gross hearing assessment. The medical record should also include the results of air and bone pure tone audiogram and speech audiometry.
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The physician’s evoked potential report should note which nerves were tested, latencies at various testing points, and an evaluation of whether the resulting values are normal or abnormal.
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Baseline testing prior to intraoperative neuromonitoring requires contemporaneous interpretation prior to the surgical procedure. To qualify for coverage of baseline testing, results of testing of multiple leads for signal strength, clarity, amplitude, etc., should be documented in the medical record. The time spent performing or interpreting the baseline electrophysiologic studies performed prior to surgery should not be counted as intraoperative monitoring, but represents separately reportable procedures. Testing performed during surgery does not qualify as baseline testing and is not a separately reportable procedure.
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For continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby) or for monitoring of more than one case while in the operating room, increments of less than 30 minutes should not be billed. For continuous intraoperative neurophysiology monitoring in the operating room with one on one monitoring requiring personal attendance, increments of less than 8 minutes should not be billed.
References
The above policy is based on the following references:
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