Tourette's Syndrome
Number: 0480
Table Of Contents
PolicyApplicable CPT / HCPCS / ICD-10 Codes
Background
References
Policy
Aetna considers certain procedures and services medically necessary for assessment and treatment of Tourette's syndrome (TS) when all of the following selection criteria are met.
- Both multiple motor and 1 or more vocal tics have been present at some time during the illness, although not necessarily simultaneously; and
- The disturbance causes significant distress or marked impairment in social, occupational, or other important areas of functioning; and
- The disturbance is not due to direct physiological effects of a substance (e.g., stimulants) or a general medical condition (e.g., Huntington's disease or post-viral encephalitis); and
- The onset is before the age of 21 years; and
- The tics occur many times a day (usually in bouts) almost every day or periodically throughout a duration of more than 1 year, and during this period there was never a tic-free period of more than 3 consecutive months.
The following procedures and services are considered medically necessary for the assessment and treatment of TS when the selection criteria outlined above are met:
-
Assessment
- Electroencephalography (EEG) or neurological consult (only in the presence of focal signs or clinical suggestions of seizure disorder or degenerative condition);
- Medical evaluation (complete medical history and physical examination)
-
Treatment
-
PharmacotherapiesFootnote1*
- Aripiprazole (Abilify)
- Clonazepam (Klonopin and generics)
- Clonidine (Catapres and generics)
- Fluphenazine (Prolixin and generics)
- Haloperidol (Haldol and generics)
- Pimozide (Orap)
- Risperidone (Risperdal)
- Tetrabenazine
- Tricyclic antidepressants (for TS members who also exhibit attention deficit hyperactivity disorder)
Footnote1* Note: Self-administered prescription medications are covered under the pharmacy benefit. Formulary restrictions may apply. Please check plan benefit description for details.
-
Psychotherapy (if member also exhibits anxiety and/or depression)
Note: Psychotherapeutic interventions are covered under the member's behavioral health benefits. Please check benefit plan descriptions.
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The following procedures and services are considered experimental and investigational for the assessment and treatment of TS because of insufficient evidence of their effectiveness for this indication:
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Assessment
- Cognitive and motor event-related potentials
- Computerized EEG (brain mapping or neurometrics, please see CPB 0221 - Quantitative EEG (Brain Mapping))
- Genetic studies
- Measurement of serum ferritin level
- MicroRNAs (miRNAs) as a biomarker
- Neuroimaging (e.g., CT, MRI, PET, and SPECT)
-
Treatment
- Acupuncture (please see CPB 0135 - Acupuncture)
- Adaptive (responsive) deep brain stimulation
- Amphetamines (amphetamine, methamphetamine) (unless there is comorbid attention-deficit hyperactivity disorder)
- Anti-glutamatergic drugs (e.g., gabapentin, lamotrigine, riluzole, and topiramate)
- Baclofen
- Bilateral stereotactic lesions of the anterior cingulate gyrus
- Bilateral thalamic stimulation/deep brain stimulation (please see CPB 0208 - Deep Brain Stimulation)
- Botox injections (please see CPB 0113 - Botulinum Toxin)
- Cannabinoids (e.g., delta-9-tetrahydrocannabidiol (THC) and nabiximols)
- Cranial electrotherapy stimulation
- Dietary interventions
- Ecopipam
- EEG biofeedback (please see CPB 0132 - Biofeedback)
- Electroconvulsive therapy
- Intravenous immunoglobulins (IVIG) (see CPB 0206 - Parenteral Immunoglobulins)
- N-acetylcysteine
- Metoclopramide
- Neurofeedback
- Omega-3 fatty acids (also known as ω-3 fatty acids or n-3 fatty acids)
- Pallidal deep brain stimulation combined with capsulotomy (for the treatment of Tourette's syndrome with psychiatric co-morbidity)
- Pramipexole
- Prefrontal cortical electrical stimulation
- Repetitive transcranial magnetic stimulation (please see CPB 0469 - Transcranial Magnetic Stimulation and Cranial Electrical Stimulation)
- Theta burst stimulation transcranial magnetic stimulation
- Transcranial direct current stimulation
- Valproate
- Valbenazine
Note: Most Aetna medical plans exclude coverage of educational interventions. Under these plans, educational and achievement testing as well as educational interventions (including classroom environmental manipulation, academic skills training, and parental training) are not covered. Please check benefit plan descriptions for details.
Background
- simple or
- complex.
There are no specific blood tests or other laboratory tests that definitively diagnose TS. Diagnosis of this disorder is a clinical one, and is made by patient history, family history, family recounting of events and behaviors of the patient, as well as by direct observation of the patient. A medical evaluation, including a complete history and physical is necessary for diagnosis. According to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), both motor and vocal tics must be present for at least 1 year to establish a diagnosis of TS. Brain mapping (computerized electroencephalography [EEG]) as well as neuroimaging studies, such as computed tomography, magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography, usually do not aid in the diagnosis of TS. Adams et al (2004) stated that the cause or causes of TS remain unknown. Functional imaging studies have evaluated several implicated neurotransmitter systems and focused predominantly on the frequency or severity of tics. The results have been inconclusive and frequently contradictory with little light shed on pathogenetic mechanisms. Electroencephalography or neurological consultation is indicated only in the presence of focal signs or clinical suggestions of seizure disorder or degenerative condition.
A working group of the European Society for the Study of Tourette Syndrome (ESSTS) has developed the first European assessment guidelines of TS (Cath et al, 2011). The available literature including national guidelines was thoroughly screened and extensively discussed in the expert group of ESSTS members. Detailed clinical assessment guidelines of tic disorders and their co-morbidities in both children and adults were presented. Screening methods that might be helpful and necessary for specialists' differential diagnosis process were suggested in order to further analyze cognitive abilities, emotional functions and motor skills. Besides clinical interviews and physical examination, additional specific tools (e.g., questionnaires, checklists and neuropsychological tests) are recommended.
- the genetic etiology of TS;
- common genetic components of TS, attention deficit hyperactivity disorder (ADHD), and obsessive compulsive disorder (OCD);
- recent linkage studies of TS;
- chromosomal translocations in TS; and
- candidate gene studies.
Dehning et al (2010) stated that TS is a complex neuropsychiatric disorder probably originating from a disturbed interplay of several neurotransmitter systems in the prefrontal-limbic-basal ganglia loop. Polygenetic multi-factorial inheritance has been postulated; nevertheless, no confirmed susceptible genes have been identified yet. As neuroimaging studies allude to dopaminergic and serotonergic dysfunction in TS and serotonin as an important factor for dopamine release, genotyping of common polymorphisms in the serotonergic receptor (HTR1A: C-1019G; HTR2A: T102C, His452Tyr, A-1438G; HTR2C: C-759T, G-697C) and transporter genes (SLC6A4) was performed in 87 patients with TS, compared with 311 matched controls. These investigators found a nominally significant association between both polymorphisms in the HTR2C and the GTS, which was more pronounced in male patients. Analysis of the further serotonergic polymorphisms did not reveal any significant result. A modified function of these promoter polymorphisms may contribute to the complex interplay of serotonin and dopamine and then to the manifestation of TS.
For most patients with TS, the clinical course is benign. For patients whose symptoms interfere with daily functioning, pharmacotherapy may help in alleviating symptoms. The most commonly used medications for the treatment of TS are haloperidol (Haldol), pimozide (Orap), fluphenazine (Prolixin), and clonidine (Catapres). Clonazepam (Klonopin) and risperidone (Risperdal) have been shown to be beneficial in some patients. Furthermore, tricyclic anti-depressants can be used for the treatment of TS patients who also exhibit attention deficit hyperactivity disorder. Psychotherapy is appropriate for TS patients who experience anxiety or depression.
There is insufficient scientific evidence to support the use of Botox (botulinum toxin) injections, biofeedback, bilateral stereotactic lesions of the anterior cingulate gyrus, bilateral thalamic stimulation, intravenous immunoglobulins and repetitive transcranial magnetic stimulation for the treatment of TS.
Maciunas et al (2007) performed a prospective double-blind cross-over trial of bilateral thalamic deep brain stimulation (DBS) in 5 adults with TS. An independent programmer established optimal stimulator settings in a single session. Subjective and objective results were assessed in a double-blind randomized manner for 4 weeks, with each week spent in 1 of 4 states of unilateral or bilateral stimulation. Results were similarly assessed 3 months after unblinded bilateral stimulator activation while repeated open programming sessions were permitted. In the randomized phase of the trial, a statistically significant (p < 0.03) reduction in the modified Rush Video-Based Rating Scale score (primary outcome measure) was identified in the bilateral on state. Improvement was noted in motor and sonic tic counts as well as on the Yale Global Tic Severity Scale and TS Symptom List scores (secondary outcome measures). Benefit was persistent after 3 months of open stimulator programming. Quality of life indices were also improved; 3 of 5 patients had marked improvement according to all primary and secondary outcome measures. The authors concluded that bilateral thalamic DBS appears to reduce tic frequency and severity in some patients with TS who have exhausted other available means of treatment. The findings of this study need to be validated by longer studies with larger sample sizes.
Visser-Vandewalle (2007) noted that following the introduction of DBS of the thalamus as a new treatment for TS in 1999, several other brain loci (e.g., globus pallidus internus, anteromedial and ventroposterolateral part, and the nucleus accumbens) have been targeted in a small number of patients. In published reports, a tic reduction rate of at least 66 % has been described. The effects of DBS on associated behavioral disorders are more variable. The number of treated patients is small and it is unclear if the effects of DBS are dependent on the target nucleus. The author stated that a meticulous evaluation of the electrode position, and a blinded assessment of the clinical effects on tics and behavioral disorders, is absolutely mandatory in order to identify the best target of DBS for TS.
- awareness training,
- relaxation training,
- competing response training (contingent), and
- contingency management.
Carr and Chong (2005) reviewed studies that used HRT to treat tics in terms of their methodological characteristics and rigor. Guidelines developed by the Task Force on Promotion and Dissemination of Psychological Procedures were used to evaluate the state of the literature. From an initial database that included 29 studies, 12 were included in the final analysis. Results indicated that although research has been conducted in this area for almost 30 years, the majority of studies contain considerable methodological shortcomings. Based on the Task Force guidelines, the existing literature on the use of HRT to treat tics can be classified as probably efficacious. Furthermore, Bloch (2008) examined the evidence base for current treatments for TS; and indicated that emerging treatments for this disorder include DBS, HRT, and repetitive transcranial magnetic stimulation.
In a Cochrane review, Curtis and colleagues (2009) evaluated the safety and effectiveness of cannabinoids as compared to placebo or other drugs in treating tics, premonitory urges and obsessive compulsive symptoms (OCS), in patients with TS. These investigators searched the Cochrane Central Register of Controlled Trials (CENTRAL) (in The Cochrane Library Issue 4 2008) , MEDLINE (January 1996 to date), EMBASE (January 1974 to date), PsycINFO (January 1887 to date), CINAHL (January 1982 to date), AMED (January 1985 to date), British Nursing Index (January 1994 to date) and DH DATA (January 1994 to date). They also searched the reference lists of located trials and review articles for further information. These researchers included randomized controlled trials (RCTs) comparing any cannabinoid preparation with placebo or other drugs used in the treatment of tics and OCS in patients with TS. Two authors abstracted data independently and settled any differences by discussion. Only 2 trials were found that met the inclusion criteria. Both studies compared a cannabinoid, delta-9-tetrahydrocannabinol (Delta(9)THC), either as monotherapy or as adjuvant therapy, with placebo. One was a double-blind, single-dose cross-over trial and the other was a double-blind, parallel-group study. A total of 28 different patients were studied. Although both trials reported a positive effect from Delta(9)THC, the improvements in tic frequency and severity were small and were only detected by some of the outcome measures. The authors concluded that there is insufficient evidence to support the use of cannabinoids in treating tics and obsessive compulsive behavior in people with TS.
In a retrospective study, Kuo and Jimenez-Shahed (2010) examined the safety and effectiveness of topiramate in the treatment of TS. Charts of subjects whose conditions were diagnosed as tic disorders seen at the authors' clinic from 2003 to 2007 were reviewed. Patients who met diagnostic criteria for TS and were started on topiramate with at least 1 follow-up visit after beginning topiramate were included. The efficacy of topiramate on a subjective scale, the global impression of response (0 = no response/worse, 1 = mild improvement, 2 = moderate improvement, 3 = marked improvement), and adverse effects were recorded for analysis. Of 453 subjects, 367 met diagnostic criteria for TS and 41 (11.1 %; 34 males) were treated with topiramate for tics for 9.43 +/- 7.03 months (range of 1 to 27 months). Mean age at onset of tics was 6.93 +/- 2.78 years (range of 2 to 14 years) and at start of topiramate treatment was 14.83 +/- 5.63 years (range of 9 to 27 years). The average efficacy on tics was 2.15 +/- 1.11, and 75.6 % (n = 31) of subjects had moderate-to-marked improvement and adverse effects included cognitive/language problems (24.4 %, n = 10) and aggression or mood swings (9.8 %, n = 4). The authors concluded that this retrospective chart review suggested that topiramate can be used for tics in TS with at least moderate efficacy and typical adverse effects. They stated that RCTs are needed.
In a a randomized, double-blind, placebo-controlled, parallel-group study, Jankovic et al (2010) examined the effects of topiramate on TS. To be included in the study, subjects required a DSM-IV diagnosis of TS, were 7 to 65 years of age, had moderate-to-severe symptoms (Yale Global Tic Severity Scale (YGTSS) greater than or equal to 19), were markedly impaired as determined by the Clinical Global Impression (CGI) scale severity score of greater than or equal to 4 and were taking no more than 1 drug each for tics or TS co-morbidities. There were 29 patients (26 males), mean age of 16.5 (SD 9.89) years, randomized, and 20 (69 %) completed the double-blind phase of the study. The primary endpoint was Total Tic Score, which improved by 14.29 (10.47) points from baseline to visit 5 (day 70) with topiramate (mean dose of 118 mg) compared with a 5.00 (9.88) point change in the placebo group (p = 0.0259). There were statistically significant improvements also in the other components of the YGTSS as well as improvements in various secondary measures, including the CGI and premonitory urge CGI. No differences were observed in the frequency of adverse events between the 2 treatment groups. The authors concluded that this study provides evidence that topiramate may have utility in the treatment of moderately severe TS. The drawbacks of this study were its small sample size, the relatively high drop-out rate (31 %), and the apparent lack of follow-up data. These findings need to be validated by further investigation.
Pourfar et al (2011) studied metabolic brain networks that are associated with TS and co-morbid OCD. These investigators utilized [(18)F]-fluorodeoxyglucose and positron emission tomography (PET) imaging to examine brain metabolism in 12 unmedicated patients with TS and 12 age-matched controls. They utilized a spatial co-variance analysis to identify 2 disease-related metabolic brain networks, one associated with TS in general (distinguishing TS subjects from controls), and another correlating with OCD severity (within the TS group alone). Analysis of the combined group of patients with TS and healthy subjects revealed an abnormal spatial co-variance pattern that completely separated patients from controls (p < 0.0001). This TS-related pattern (TSRP) was characterized by reduced resting metabolic activity of the striatum and orbito-frontal cortex associated with relative increases in pre-motor cortex and cerebellum. Analysis of the TS cohort alone revealed the presence of a second metabolic pattern that correlated with OCD in these patients. This OCD-related pattern (OCDRP) was characterized by reduced activity of the anterior cingulate and dorso-lateral pre-frontal cortical regions associated with relative increases in primary motor cortex and precuneus. Subject expression of OCDRP correlated with the severity of this symptom (r = 0.79, p < 0.005). The authors concluded that these findings suggested that the different clinical manifestations of TS are associated with the expression of 2 distinct abnormal metabolic brain networks. These, and potentially other disease-related spatial co-variance patterns, may prove useful as biomarkers for assessing responses to new therapies for TS and related co-morbidities. Furthermore, they noted that more studies are needed to evaluate the expression of TSRP and OCDRP patterns in larger patient and control cohorts, ideally including non-TS-associated OCD. It is important to ascertain if existing or novel therapeutic interventions can suppress the activity of these and related functional brain networks. If validated in independent populations, and found to be reproducible, these patterns may be useful as adjunctive outcome measures in clinical trials. One of the drawbacks of this study was that subjects were all adults (mostly men) and the symptoms were "mild" as they did not require treatment with medication.
Ackermans et al (2011) stated that DBS of the thalamus has been proposed as a therapeutic option in patients with TS who are refractory to pharmacological and psychotherapeutic treatment. Patients with intractable TS were invited to take part in a randomized, double-blind, cross-over study evaluating the safety and effectiveness of stimulation of the centromedian nucleus-substantia periventricularis-nucleus ventro-oralis internus cross-point in the thalamus. After surgery, the patients were randomly assigned to 3 months stimulation followed by 3 months OFF stimulation (group A) or vice versa (group B). The cross-over period was followed by 6 months ON stimulation. Assessments were performed prior to surgery and at 3, 6 months and 1 year after surgery. The primary outcome was a change in tic severity as measured by the Yale Global Tic Severity Scale and the secondary outcome was a change in associated behavioral disorders and mood. Possible cognitive side effects were studied during stimulation ON at 1 year post-operatively. Interim analysis was performed on a sample of 6 male patients with only 1 patient randomized to group B. Tic severity during ON stimulation was significantly lower than during OFF stimulation, with substantial improvement (37 %) on the Yale Global Tic Severity Scale (mean 41.1 +/- 5.4 versus 25.6 +/- 12.8, p = 0.046). The effect of stimulation 1 year after surgery was sustained with significant improvement (49 %) on the Yale Global Tic Severity Scale (mean 42.2 +/- 3.1 versus 21.5 +/- 11.1, p = 0.028) when compared with pre-operative assessments. Secondary outcome measures did not show any effect at a group level, either between ON and OFF stimulation or between pre-operative assessment and that at 1 year post-operatively. Cognitive re-assessment at 1 year after surgery showed that patients needed more time to complete the Stroop Colour Word Card test. This test measures selective attention and response inhibition. Serious adverse events included 1 small hemorrhage ventral to the tip of the electrode, 1 infection of the pulse generator, subjective gaze disturbances and reduction of energy levels in all patients. The authors concluded that these preliminary findings suggest that stimulation of the centromedian nucleus-substantia periventricularis-nucleus ventro-oralis internus cross-point may reduce tic severity in refractory TS, but there is the risk of adverse effects related to oculo-motor function and energy levels. They stated that further RCTs on other targets are urgently needed since the search for the optimal one is still ongoing.
The European clinical guideline for "Tourette syndrome and other tic disorders. Part IV: Deep brain stimulation" (Muller-Vahl et al, 2011) stated that "[a]t present time, DBS in TS is still in its infancy. Due to both different legality and practical facilities in different European countries these guidelines, therefore, have to be understood as recommendations of experts. However, among the ESSTS working group on DBS in TS there is general agreement that, at present time, DBS should only be used in adult, treatment resistant, and severely affected patients. It is highly recommended to perform DBS in the context of controlled trials".
- what patients with TS should be treated with DBS, and
- what is the best target?
- intent-to-treat design, with the last-observation-carried-forward controlling for baseline measures and ADHD via
- logistic regression, comparing percentage of responders on the primary Yale Global Tic Severity Scale (YGTSS)-Tic and secondary (YGTSS-Global and YGTSS-Impairment) outcome measures and
- analysis of covariance; and
- longitudinal mixed-effects models.
Wenzel et al (2012) stated that aripiprazole is an atypical neuroleptic with agonistic and antagonistic dopaminergic and serotonergic effects. Because preliminary data obtained from uncontrolled studies suggested that aripiprazole may be effective in the treatment of tics, these investigators performed a retrospective study with a large group of patients with TS. A total of 100 patients (78 men and 22 women; mean +/- SD age, 27.1 years (+/- 11.5) years) who had been treated with daily doses of 5 to 45 mg (mean, 17.0 +/- 9.6 mg) aripiprazole at the authors’ specialized TS outpatient clinic were included; 95 patients with insufficient pre-treatment (1 or more neuroleptics) were switched to aripiprazole. Eighty-two patients exhibited a considerable reduction in tic severity. In 48 patients, effective treatment lasted for more than 12 months. Five patients reported additional beneficial effects on behavioral co-morbidities such as depression, anxiety, and auto-aggression. Altogether, 31 patients (31 %) dropped out of the treatment owing to inefficacy (n = 7), adverse effects (n = 15: drowsiness, agitation, weight gain, and sleep disturbances), both (n = 4) or other reasons (n = 5). The authors concluded that this study was the largest case series on the treatment of tics with aripiprazole so far. Overall, these findings corroborated previous data suggesting that aripiprazole is safe and effective in most patients. In particular, these data confirmed effectiveness in adult patients and clarified that beneficial effects sustain. However, in contrast to previous data, in 1 of 3 of the highly selected patients, aripiprazole was ineffective or not well-tolerated. Optimal dose seems to be individually different and may range from 5 to 45 mg.
Waldon et al (2013) the pharmacological treatment of TS focuses on the modulation of monoaminergic pathways within the cortico-striato-thalamo-cortical circuitry. These investigators evaluated the safety and effectiveness of pharmacological agents used in the treatment of tics in patients with TS, in order to provide clinicians with an evidence-based rationale for the pharmacological treatment in TS. In order to ascertain the best level of evidence, these researchers conducted a systematic literature review to identify double-blind RCTs of medications in TS populations. They identified a large number of pharmacological agents as potentially effective in improving tic symptoms. The alpha-2 agonist clonidine is among the agents with the most favorable efficacy-versus-adverse events ratio, especially in patients with co-morbid ADHD, although effect sizes vary evidence-based studies. The authors concluded that these findings are in line with the findings of uncontrolled open-label studies. However, most trials have low statistical power due to the small sample sizes, and newer agents, such as aripiprazole, have not been formally tested in double-blind RCTs. They stated that further research should focus on better outcome measures, including Quality of Life instruments.
An UpToDate review on “Tourette syndrome” (Jankovic, 2014) states that “A possible approach to improve symptoms is reduction of hyperexcitability in the motor and premotor cortex. In a small single-blinded, placebo-controlled, crossover trial in patients with TS, repetitive transcranial magnetic stimulation to reduce activity in these areas did not improve symptoms. Patients with disabling tics that are refractory to optimal medical management may be candidates for deep brain stimulation of globus pallidus, thalamus or other subcortical targets. However, the available evidence is preliminary, and large clinical trials are needed to determine whether DBS is beneficial for controlling tics in patients with TS”.
Chen et al (2012) examined the clinical efficacy and tolerability of tetrabenazine (TBZ) in the management of dystonia, Huntington chorea, tardive dyskinesia (TDk), and tic disorders. A Cochrane Library, EMBASE, MedlinePlus, PubMed, and clinical trials database search (up to May 2012) was conducted to identify articles and studies using the subject terms tetrabenazine, Huntington disease, dystonia, tardive dyskinesia, Tourette, tics, and hyperkinetic movement. Only English-language articles were reviewed. Tetrabenazine variably undergoes extensive first-pass metabolism to active metabolites, some of which are metabolized by the cytochrome P450 2D6 isozyme. Pharmacology studies demonstrate that TBZ reversibly inhibits the activity of vesicular monoamine transporter 2, resulting in depletion of central dopamine. For management of dystonias, 1 of 3 small prospective blinded studies and 4 of 5 retrospective studies reported clinical benefit with TBZ use in pediatrics and adults. For Huntington chorea, 2 randomized, double-blind, placebo-controlled studies along with open-label studies demonstrated the effectiveness of TBZ in adults. For TDk, 9 of 11 studies (prospective controlled and retrospective) reported positive benefit. For TS, 9 of 11 studies (prospective controlled and retrospective) reported positive benefit on motor and phonic tics in pediatric and adult patients. Overall, adverse effects are dose- and age-related; and included depression, fatigue, parkinsonism, and somnolence. The authors concluded that TBZ is an effective oral therapy for chorea of Huntington disease and may be considered as an alternative agent for the management of dystonia, TDk, and tic disorders (these latter 3 conditions are off-label uses in the United States). The drug possesses an acceptable tolerability profile and has been used in pediatric and adult populations.
In the Canadian guidelines for the evidence-based treatment of tic disorders: Pharmacotherapy, Pringsheim et al (2012) performed a systematic review of the literature on the treatment of tic disorders. A multi-institutional group of 14 experts in psychiatry, child psychiatry, neurology, pediatrics, and psychology engaged in a consensus meeting. The evidence was presented and discussed, and nominal group techniques were employed to arrive at consensus on recommendations. A strong recommendation is made when the benefits of treatment clearly outweigh the risks and burdens, and can apply to most patients in most circumstances without reservation. With a weak recommendation, the benefits, risks, and burdens are more closely balanced, and the best action may differ depending on the circumstances. Based on these principles, weak recommendations were made for the use of pimozide, haloperidol, fluphenazine, metoclopramide (children only), risperidone, aripiprazole, olanzapine, quetiapine, ziprasidone, topiramate, baclofen (children only), botulinum toxin injections, TBZ, and cannabinoids (adults only). Strong recommendations were made for the use of clonidine and guanfacine (children only). While the evidence supported the efficacy of many of the anti-psychotics for the treatment of tics, the high rates of side effects associated with these medications resulted in only weak recommendations for these drugs. In situations where tics are not severe or disabling, the use of a medication with only a weak recommendation is not warranted. However, when tics are more distressing and interfering, the need for tic suppression to improve quality of life is stronger, and patients and clinicians may be more willing to accept the risks of pharmacotherapy.
Also, an UpToDate review on “Tourette syndrome” (Jankovic, 2014) states that “We treat tics with drugs that block dopamine receptors, such as fluphenazine, pimozide, and tetrabenazine, which depletes neuronal dopamine. These drugs appear to have a similar response rate, reducing the frequency and intensity of tics by approximately 60 to 80 percent. In our experience, these drugs are more effective and better tolerated than haloperidol. Tetrabenazine, which depletes dopamine by inhibiting vesicular monoamine transporter type 2 (VMAT2), is particularly useful because it is as effective as the typical neuroleptics, but it does not cause tardive dyskinesias …. For patients with TS and bothersome tics, we recommend drugs such as fluphenazine starting at 1 mg daily, pimozide starting at 2 mg daily, or tetrabenazine starting at 12.5 mg daily”.
Termine et al (2013) noted that TS is a neurodevelopmental disorder characterized by multiple motor/phonic tics and a wide spectrum of behavioral problems (e.g., complex tic-like symptoms, attention deficit hyperactivity disorder, and obsessive-compulsive disorder). It can be a challenging condition even for the specialists, because of the complexity of the clinical picture and the potential adverse effects of the most commonly prescribed medications. Regarding non-pharmacological interventions for TS, some of the more recent treatments that have been studied include electro-convulsive therapy and repetitive transcranial magnetic stimulation (rTMS). The authors focused primarily on the safety and effectiveness of these emerging treatment strategies in TS.
The Tourette Syndrome Association International Deep Brain Stimulation (DBS) Database and Registry Study Group (Schrock et al, 2015) stated that “ Tourette syndrome patients represent a unique and complex population, and studies reveal a higher risk for post-DBS complications. Successes and failures have been reported for multiple brain targets; however, the optimal surgical approach remains unknown. Tourette syndrome DBS, though still evolving, is a promising approach for a subset of medication refractory and severely affected patients”.
Anti-Glutamatergic Drugs and Vesicular Monoamine Transporter Type 2 Inhibitors
Kious et al (2016) reviewed strategies for the management of TS. These investigators considered emerging treatments for refractory cases, including DBS, electroconvulsive therapy (ECT), rTMS, and novel pharmacological approaches (e.g., anti-glutamatergic drugs, cannabinoids, and new vesicular monoamine transporter type 2 inhibitors).
Mindfulness-Based Stress Reduction
- to determine the feasibility and acceptability of an 8-week trial of MBSR-tics in individuals 16 and older with TS or CTD, and
- to determine the effectiveness of an 8-week trial of MBSR-tics in individuals 16 and older with TS or CTD.
N-Acetylcysteine
In a randomized, double-blind, placebo-controlled clinical trial, Bloch et al (2016) examined the effectiveness of N-acetylcysteine (NAC) for the treatment of pediatric TS. A total of 31 children and adolescents 8 to 17 years of age with TS were randomly assigned to receive NAC or matching placebo for 12 weeks. The primary outcome was change in severity of tics as measured by the YGTSS, and Total tic score. Secondary measures assessed co-morbid OCD, depression, anxiety, and ADHD. Linear mixed models in SAS were used to examine differences between NAC and placebo. Of the 31 randomized subjects, 14 were assigned to placebo (2 females; 11.5 +/- 2.8 years) and 17 to active NAC (5 females; 12.4 +/- 1.4 years) treatment. No significant difference between NAC and placebo was found in reducing tic severity or any secondary outcomes. The authors concluded that they found no evidence for effectiveness of NAC in treating tic symptoms. They stated that these findings stood in contrast to studies suggesting benefits of NAC in the treatment of other obsessive-compulsive spectrum disorders in adults, including OCD and trichotillomania, but were similar to a recent placebo-controlled trial of pediatric trichotillomania that found no benefit of NAC.
Valproate
In a systematic review and meta-analysis, Yang and colleagues (2015) evaluated the safety and effectiveness of sodium valproate for children with TS. These investigators searched PubMed, EMBASE, the Cochrane library, Cochrane Central, CBM, CNKI, VIP, WANG FANG database and relevant reference lists. A total of 5 RCTs (n = 247) and 5 case series (n = 163) studies were included. Only 1 RCT (n = 93) evaluated total YGTSS scores and there was significant difference in the reduction of total YGTSS scores between sodium valproate and the control group (3.50 ± 4.59 versus 7.86 ± 7.03, p < 0.01). One RCT (n = 30) evaluated motor and vocal tics, and there was significant difference in the reduction of motor and vocal tics scores between sodium valproate and haloperidol (10.45 ± 4.15 versus 14.92 ± 3.01, p < 0.01). Meta-analysis of 3 RCTs (n = 124) showed there was no significant difference in the reduction of the number of tics between sodium valproate and the positive control group (relative risk (RR) = 1.09, 95 % confidence interval [CI]: 0.92 to 1.30, p = 0.30). The pooled proportion in 5 case series studies which used tics symptom improvement self-defined by authors was 80.7 % (95 % CI: 73.7 to 86.2, I(2) = 0). No fatal side effects were reported. The authors concluded that based on the limited evidence, the routine use of sodium valproate for treatment of TS in children is not recommended; further well-conducted trials that examine long-term outcomes are needed.
Tetrabenazine
Paleacu et al (2004) tetrabenazine (TBZ) is a catecholamine depletor used for the treatment of a variety of movement disorders. The purpose of this study was to assess the efficacy of TBZ in a retrospective chart review in 3 tertiary care movement disorders centers over long-term treatment. Of 150 patients to whom TBZ was prescribed, 118 were followed-up and assessed using the Clinical Global Impression of Change (CGIC), (-3 to +3), a composite grade from a patient and caregiver scale over variable periods. The patients had a variety of hyperkinetic movement disorders including dystonia (generalized and focal: axial, Meige syndrome, torticollis, blepharospasm, bruxism), Huntington disease (HD) or other choreas, tardive dyskinesia (TD) or akathisia, and Tourette syndrome. Mean patient age was 48.8 +/- 18.7 years; 48 were men (40.7 %) with a mean disease duration of 93 months. The mean follow-up time was 22 months and the mean TBZ dose was 76.2 +/- 22.5 mg/d (median of 75 mg, range of 25 to 175 mg/d). The mean CGIC score was +1 (mild improvement). The group of patients who scored +3 on the CGIC (very good improvement) represented 18.6 % (n = 22) of all patients. They had HD or other types of chorea 7.6 % (n = 9), facial dystonia/dyskinesia (n = 7, 5.9 %), 1 with TD, 2 with trunk dystonia, 2 with Tourette syndrome, and 1 with tardive akathisia. This group had the longest treatment duration and received a mean TBZ dose of 70.5 mg/d (median of 75 mg/d) for a mean of 25.4 +/- 21.3 months. The authors concluded that TBZ is a moderately effective treatment of a large variety of hyperkinetic movement disorders, with excellent effects in a subgroup with chorea and facial dystonia/dyskinesias.
Lopez Del Val et al (2009) noted that TBZ is a benzoquinolizine with a high anti-dopaminergic potential due to a monoamine depletion effect that acts equally on the three main neurotransmitters (dopamine, noradrenalin and serotonin). This potentially explains why this group of pharmaceutical agents has been used for years to treat different types of hyperkinetic syndromes. These researchers examined both the pharmacokinetic and the pharmacodynamic characteristics of TBZ. A thorough review was performed of the literature on the main indications established over the years for the therapeutic utilization of TBZ, the most important hyperkinetic syndromes of which include: tardive dyskinesias, athetosis, ballism, dystonias (primary, tardive, etc.,), tics or Tourette syndrome, and finally the semiological group consisting of choreas (Huntington's disease, Sydenham's chorea and other pediatric choreas). The authors concluded that TBZ appears to be an excellent pharmacological agent for use in a number of pathologies that are accompanied by hyperkinesias; it is well-tolerated and has few complications or side effects deriving from its administration.
Chen et al (2012) examined the clinical efficacy and tolerability of TBZ in the management of dystonia, Huntington chorea, tardive dyskinesia (TDk), and tic disorders. A Cochrane Library, EMBASE, MedlinePlus, PubMed, and clinical trials database search (up to May 2012) was conducted to identify articles and studies using the subject terms tetrabenazine, Huntington disease, dystonia, tardive dyskinesia, Tourette, tics, and hyperkinetic movement. Only English-language articles were reviewed. TBZ variably undergoes extensive first-pass metabolism to active metabolites, some of which are metabolized by the cytochrome P450 2D6 isozyme. Pharmacology studies demonstrate that TBZ reversibly inhibits the activity of vesicular monoamine transporter 2, resulting in depletion of central dopamine. For management of dystonias, 1 of 3 small prospective blinded studies and 4 of 5 retrospective studies reported clinical benefit with TBZ use in pediatrics and adults. For Huntington chorea, 2 randomized, double-blind, placebo-controlled studies along with open-label studies demonstrate the effectiveness of TBZ in adults. For TDk, 9 of 11 studies (prospective controlled and retrospective) reported positive benefit. For Gilles de la Tourette syndrome, 9 of 11 studies (prospective controlled and retrospective) reported positive benefit on motor and phonic tics in pediatric and adult patients. Overall, adverse effects are dose- and age-related; and included depression, fatigue, parkinsonism, and somnolence. The authors concluded that TBZ is an effective oral therapy for chorea of Huntington disease and may be considered as an alternative agent for the management of dystonia, TDk, and tic disorders (these latter 3 conditions are off-label uses in the United States). The drug possesses an acceptable tolerability profile and has been used in pediatric and adult populations.
The Canadian guidelines for the evidence-based treatment of tic disorders: Pharmacotherapy (Pringsheim et al, 2012) performed a systematic review of the literature on the treatment of tic disorders. A multi-institutional group of 14 experts in psychiatry, child psychiatry, neurology, pediatrics, and psychology engaged in a consensus meeting. The evidence was presented and discussed, and nominal group techniques were employed to arrive at consensus on recommendations. A strong recommendation is made when the benefits of treatment clearly outweigh the risks and burdens, and can apply to most patients in most circumstances without reservation. With a weak recommendation, the benefits, risks, and burdens are more closely balanced, and the best action may differ depending on the circumstances. Based on these principles, weak recommendations were made for the use of pimozide, haloperidol, fluphenazine, metoclopramide (children only), risperidone, aripiprazole, olanzapine, quetiapine, ziprasidone, topiramate, baclofen (children only), botulinum toxin injections, TBZ, and cannabinoids (adults only). Strong recommendations were made for the use of clonidine and guanfacine (children only). While the evidence supports the efficacy of many of the antipsychotics for the treatment of tics, the high rates of side effects associated with these medications resulted in only weak recommendations for these drugs. In situations where tics are not severe or disabling, the use of a medication with only a weak recommendation is not warranted. However, when tics are more distressing and interfering, the need for tic suppression to improve quality of life is stronger, and patients and clinicians may be more willing to accept the risks of pharmacotherapy.
Also, an UpToDate review on “Tourette syndrome” (Jankovic, 2017) states that “For patients with TS who have tics that are mild and nondisabling, we suggest education and counseling without pharmacologic tic suppression therapy (Grade 2C). For patients with TS and bothersome tics, we suggest medication treatment with tetrabenazine starting at 12.5 mg daily (Grade 2C). For patients with TS who have only focal motor or vocal tics, we suggest treatment with botulinum toxin injections into the affected muscles (Grade 2C). For patients with TS and bothersome tics who either prefer nonpharmacologic treatment or who have not tolerated or responded to pharmacologic interventions, we suggest behavioral therapy with habit reversal training, where available (Grade 2B)”.
Acupuncture
Yu and colleagues (2016) searched for RCTs using acupuncture to treat TS written in English or Chinese without restrictions on publication status. Study selection, data extraction, and assessment of study quality were conducted independently by 2 reviewers. Meta-analyses were performed using Review Manager (RevMan) 5.3 software from the Cochrane Collaboration. Data were combined with the fixed-effect model based on a heterogeneity test. Results were presented as risk ratios for dichotomous data and mean differences (MDs) for continuous data. This review included 7 RCTs with a total of 564 participants. The combined results showed that acupuncture may have better short-term effect than Western medicine for TS and that acupuncture may be an effective adjuvant therapy in improving the effect of Western medicine on TS, but the evidence is limited because of existing biases. The authors concluded that there is a need for large-scale and well-designed RCTs of acupuncture for TS with rigorous methods of randomization, blinding, and adequately concealed allocation, as well as validated outcome measures; and all information including adverse effects should be reported in detail.
Dietary Interventions
Whittington and associates (2016) conducted a systematic review of interventions for children and young people with TS. Databases were searched from inception to 1 October 2014 for placebo-controlled trials of pharmacological, behavioral, physical or alternative interventions for tics in children and young people with TS or CTD. Certainty in the evidence was assessed with the GRADE approach. A total of 40 trials were included [pharmacological (32), behavioral (5), physical (2), dietary (1)]. For tics/global score there was evidence favoring the intervention from 4 trials of α2-adrenergic receptor agonists [clonidine and guanfacine, standardized MD (SMD) = -0.71; 95 % CI: -1.03 to -0.40; n = 164] and 2 trials of HRT/comprehensive behavioral intervention (CBIT) (SMD = -0.64; 95 % CI: -0.99 to -0.29; n = 133). Certainty in the effect estimates was moderate. A post-hoc analysis combining oral clonidine/guanfacine trials with a clonidine patch trial continued to demonstrate benefit (SMD = -0.54; 95 % CI: -0.92 to -0.16), but statistical heterogeneity was high. Evidence from 4 trials suggested that anti-psychotic drugs improved tic scores (SMD = -0.74; 95 % CI: -1.08 to -0.40; n = 76), but certainty in the effect estimate was low. The evidence for other interventions was categorized as low or very low quality, or showed no conclusive benefit. The authors concluded that when medication is considered appropriate for the treatment of tics, the balance of clinical benefits to harm favors α2-adrenergic receptor agonists (clonidine and guanfacine) as first-line agents. Anti-psychotics are likely to be useful but carry the risk of harm and so should be reserved for when α2-adrenergic receptor agonists are either ineffective or poorly tolerated. They stated that there is evidence that HRT/CBIT is effective, but there is no evidence for HRT/CBIT alone relative to combining medication and HRT/CBIT. Moreover, they noted that there is currently no evidence to suggest that the physical and dietary interventions reviewed are sufficiently effective and safe to be considered as treatments.
Measurement of Serum Ferritin Level
Ghosh and Burkman (2017) stated that tics can be considered hyperkinetic movements akin to restless leg syndrome (RLS). Drawing the analogy of iron deficiency as an etiology of RLS, it is conceivable that iron deficiency may underlie or worsen tics in TS. These investigators evaluated the relationship between serum ferritin levels and tic severity, as well as consequent impact on life, in children with TS. Children less than 18 years of age, diagnosed with TS during 2009 to 2015, were reviewed. Only those with serum ferritin testing were included. The following data were collected: tic severity, impact on life, medication, co-morbidities, blood count, and serum ferritin at diagnosis and follow-up. In 57 patients, male to female ratio of 2:1, serum ferritin was 48.0 ± 33.28 ng/ml, tic severity score 2.3 ± 0.80, impact on life score 2.2 ± 0.93, and composite score 4.57 ± 1.6. Serum ferritin was not influenced by co-morbid obsessive compulsive disorder (OCD), attention deficit hyperactive disorder (ADHD), or anxiety (p > 0.16); 38 % with low serum ferritin (less than or equal to 50 ng/ml) (n = 37) had severe tics (greater than 5 composite score), compared with 25 % in normal ferritin group (n = 20). Over 6 to 12 months, tic severity score improved in both iron-treated groups, deficient (2.70 to 1.90) and sufficient (2.40 to 1.95), whereas tics worsened or remained the same when not treated with iron. The authors concluded that these findings suggested that iron deficiency may be associated with more severe tics with higher impact on TS children, independent of the presence of OCD, ADHD, or anxiety. Iron supplementation showed a trend towards improvement of tic severity upon follow-up. These researchers suggested a double-blind, placebo-controlled, prospective study to reach a definite conclusion.
Botulinum Toxin
In a Cochrane review, Pandey and colleagues (2018) determined the safety and effectiveness of botulinum toxin in treating motor and phonic tics in people with TS, and to analyzed the effect of botulinum toxin on premonitory urge and sensory tics. These investigators searched the Cochrane Movement Disorders Group Trials Register, CENTRAL, Medline, and 2 trials registers to October 25, 2017. They reviewed reference lists of relevant articles for additional trials. These researchers considered all randomized, controlled, double-blind studies comparing botulinum toxin to placebo or other medications for the treatment of motor and phonic tics in TS for this review. They sought both parallel group and cross-over studies of children or adults, at any dose, and for any duration. These researchers followed standard Cochrane methods to select studies, assess risk of bias, extract and analyze data. All authors independently abstracted data onto standardized forms; disagreements were resolved by mutual discussion. Only 1 randomized, placebo-controlled, double-blind, cross-over study met the selection criteria. In this study, a total of 20 participants with motor tics were enrolled over a 3-year recruitment period; 18 (14 of whom had a diagnosis of TS) completed the study; in total, 21 focal motor tics were treated. Although these investigators considered most bias domains to be at low risk of bias, the study recruited a small number of participants with relatively mild tics and provided limited data for the key outcomes. The effects of botulinum toxin injections on tic frequency, measured by videotape or rated subjectively, and on premonitory urge, were uncertain (very low-quality evidence). The quality of evidence for adverse events following botulinum toxin was very low; 9 people had muscle weakness following the injection, which could have led to un-blinding of treatment group assignment. No data were available to evaluate whether botulinum injections led to immuno-resistance to botulinum. The authors concluded that they were uncertain about botulinum toxin effects in the treatment of focal motor and phonic tics in select cases since the quality of the evidence as very low. Moreover, they stated that additional RCTs are needed to demonstrate the benefits and harms of botulinum toxin therapy for the treatment of motor and phonic tics in patients with TS.
Deep Brain Stimulation
In a randomized, double-blind, controlled trial, Welter and colleagues (2017) evaluated the efficacy of anterior internal globus pallidus (aGPi) DBS for patients with severe TS. Patients aged 18 to 60 years with severe and medically refractory TS from 8 hospitals specialized in movement disorders in France were recruited for this study. Enrolled patients received surgery to implant bilateral electrodes for aGPi DBS; 3 months later they were randomly assigned (1:1 ratio with a block size of 8; computer-generated pairwise randomization according to order of enrolment) to receive either active or sham stimulation for the subsequent 3 months in a double-blind fashion . All patients then received open-label active stimulation for the subsequent 6 months. Patients and clinicians assessing outcomes were masked to treatment allocation; an unmasked clinician was responsible for stimulation parameter programming, with intensity set below the side-effect threshold. The primary end-point was difference in YGTSS score between the beginning and end of the 3 month double-blind period, as assessed with a Mann-Whitney-Wilcoxon test in all randomly allocated patients who received active or sham stimulation during the double-blind period. These researchers assessed safety in all patients who were enrolled and received surgery for aGPi DBS. Between December 6, 2007 and December 13, 2012, a total of 19 patients were enrolled. The authors randomly assigned 17 (89 %) patients, with 16 completing blinded assessments (7 [44 %] in the active stimulation group and 9 [56 %] in the sham stimulation group). These researchers noted no significant difference in YGTSS score change between the beginning and the end of the 3 month double-blind period between groups (active group median YGTSS score 68.5 [inter-quartile range [IQR] 34.0 to 83.5] at the beginning and 62.5 [51.5 to 72.0] at the end, median change 1.1 % [IQR -23.9 to 38.1]; sham group 73.0 [69.0 to 79.0] and 79.0 [59.0 to 81.5], median change 0.0 % [-10.6 to 4.8]; p=0.39). A total of 15 serious adverse events (SAEs; 3 in patients who withdrew before stimulation and 6 each in the active and sham stimulation groups) occurred in 13 patients (3 who withdrew before randomization, 4 in the active group, and 6 in the sham group), with infections in DBS hardware in 4 patients (2 who withdrew before randomization, 1 in the sham stimulation group, and 1 in the active stimulation group). Other SAEs included 1 electrode misplacement (active stimulation group), 1 episode of depressive signs (active stimulation group), and 3 episodes of increased tic severity and anxiety (2 in the sham stimulation group and 1 in the active stimulation group). The authors concluded that 3 months of aGPi DBS was insufficient to decrease tic severity for patients with TS. Moreover, they stated that future research is needed to examine the efficacy of aGPi DBS for patients over longer periods with optimal stimulation parameters and to identify potential predictors of the therapeutic response.
Jo and co-workers (2018) stated that DBS of the thalamus is a promising therapeutic alternative for treating medically refractory TS. However, few human studies have examined its mechanism of action. Therefore, the networks that mediate the therapeutic effects of thalamic DBS remain poorly understood. In this study, a total of 5 participants diagnosed with severe medically refractory TS underwent bilateral thalamic DBS stereotactic surgery. Intra-operative functional magnetic resonance imaging (fMRI) characterized the blood oxygen level-dependent (BOLD) response evoked by thalamic DBS and examined if the therapeutic effectiveness of thalamic DBS, as assessed using the Modified Rush Video Rating Scale (RVRS) test, would correlate with evoked BOLD responses in motor and limbic cortical and subcortical regions. The results reveal that thalamic stimulation in TS participants had wide-ranging effects that impact the fronto-striatal, limbic, and motor networks. Thalamic stimulation induced suppression of motor and insula networks correlated with motor tic reduction, while suppression of frontal and parietal networks correlated with vocal tic reduction. These regions mapped closely to major regions of interest (ROI) identified in a non-human primate model of TS. The authors concluded that these findings suggested that a critical factor in TS treatment should involve modulation of both fronto-striatal and motor networks, rather than be treated as a focal disorder of the brain. Using the novel combination of DBS-evoked tic reduction and fMRI in human subjects, these researchers provided new insights into the basal ganglia-cerebellar-thalamo-cortical network-level mechanisms that influence the effects of thalamic DBS. They stated that future translational research should identify whether these network changes are cause or effect of TS symptoms.
Per the International Tourette Syndrome Deep Brain Stimulation Public Database and Registry, Martinez-Ramirez and colleagues (2018) stated that DBS is a promising therapy for TS. Moreover, these investigators noted that DBS was associated with symptomatic improvement in patients with TS but also with important AEs. Furthermore, Martino and Pringsheim (2018) stated that DBS is a potential option for medically refractory, severely disabled patients with tics, but age and target selection require further investigation.
Adaptive (Responsive) Deep Brain Stimulation
Marceglia and colleagues (2017) noted that DBS has emerged as a novel therapy for the treatment of several movement and neuropsychiatric disorders, and may also be suitable for the treatment of TS. The main DBS targets used to date in patients with TS are located within the basal ganglia-thalamo-cortical circuit involved in the pathophysiology of this syndrome. They include the ventralis oralis/centromedian-parafascicular (Vo/CM-Pf) nucleus of the thalamus and the nucleus accumbens. Current DBS treatments deliver continuous electrical stimulation and are not designed to adapt to the patient's symptoms, thereby contributing to unwanted side effects. Moreover, continuous DBS can lead to rapid battery depletion, which necessitates frequent battery replacement surgeries. Adaptive DBS (aDBS), which is based on neurophysiological biomarkers, is considered one of the most promising approaches to optimize clinical benefits and to limit the side effects of DBS. Adaptive DBS consists of a closed-loop system designed to measure and analyze a control variable reflecting the patient's clinical condition and to modify on-line stimulation settings to improve treatment efficacy. Local field potentials (LFPs), which are sums of pre- and post-synaptic activity arising from large neuronal populations, directly recorded from electrodes implanted for DBS can theoretically represent a reliable correlate of clinical status in patients with TS. The well-established LFP-clinical correlations in patients with Parkinson's disease reported in the last few years provide the rationale for developing and implementing new aDBS devices whose efficacies are under evaluation in humans. Only a few studies have investigated LFP activity recorded from DBS target structures and the relationship of this activity to clinical symptoms in TS. These investigators reviewed the available literature supporting the feasibility of an LFP-based aDBS approach in patients with TS. In addition, to increase such knowledge, these researchers reported explorative findings regarding LFP data recently acquired and analyzed in patients with TS after DBS electrode implantation at rest, during voluntary and involuntary movements (tics), and during ongoing DBS. Data available up to now suggested that patients with TS have oscillatory patterns specifically associated with the part of the brain they are recorded from, and thereby with clinical manifestations. The Vo/CM-Pf nucleus of the thalamus is involved in movement execution and the pathophysiology of TS. Moreover, the oscillatory patterns in TS are specifically modulated by DBS treatment, as reflected by improvements in TS symptoms. The authors concluded that these findings suggested that LFPs recorded from DBS targets may be used to control new aDBS devices capable of adaptive stimulation responsive to the symptoms of TS. Moreover, they stated that further studies are needed to better understand the LFP signatures of psychiatric co-morbidities and non-tic disease manifestations. These studies should include other DBS targets that are now considered very promising for the treatment of TS, such as the anterior globus pallidus internus.
Molina and associates (2018) stated that DBS has emerged as a promising intervention for the treatment of select movement and neuropsychiatric disorders. Current DBS therapies deliver electrical stimulation continuously and are not designed to adapt to a patient's symptoms. Continuous DBS can lead to rapid battery depletion, which necessitates frequent surgery for battery replacement. Next-generation neuro-stimulation devices can monitor neural signals from implanted DBS leads, where stimulation can be delivered responsively, moving the field of neuromodulation away from continuous paradigms. To this end, these researchers designed and chronically implemented a responsive stimulation paradigm in a patient with medically refractory TS. The patient underwent implantation of a responsive neuro-stimulator, which was capable of responsive DBS, with bilateral leads in the centromedian-parafascicular (Cm-Pf) region of the thalamus. A spectral feature in the 5- to 15-Hz band was identified as the control signal. Clinical data collected prior to and after 12 months of responsive therapy revealed improvements from baseline scores in both Modified Rush Tic Rating Scale and Yale Global Tic Severity Scale scores (64 % and 48 % improvement, respectively). The effectiveness of responsive stimulation (p = 0.16) was statistically identical to that of scheduled duty cycle stimulation (p = 0.33; 2-sided Wilcoxon unpaired rank-sum t-test). The authors concluded that responsive DBS resulted in a 63.3 % improvement in the neuro-stimulator's projected mean battery life. These researchers presented the first proof-of-concept for responsive DBS in a patient with TS.
Investigational Pharmacological Agents
Kanaan and colleagues (2017) noted that early anecdotal reports and preliminary studies suggested that cannabinoid-based medicines such as delta-9-tetrahydrocannabinol (THC) are effective in the treatment of Gilles de la TS. These investigators reported a single case study of a patient with otherwise treatment-resistant TS successfully treated with nabiximols. The patient was a 22-year old man suffering from severe and complex TS. Treatment with nabiximols was commenced at a dose of 1 puff/day (= 100 μL containing 2.7 mg THC and 2.5 mg cannabidiol (CBD)) and slowly increased up to a dosage of 3 × 3 puffs/day (= 24.3 mg THC and 22.5 mg CBD). Several clinical measures for tics, premonitory urges, and global impairment were acquired before and after 2 weeks of treatment. Treatment with nabiximols resulted in major improvements of both tics and premonitory urges, but also global impairment and health-related quality of life (QOL) according to all used measurements without causing relevant adverse effects. These findings provided further evidence that treatment with nabiximols may be effective in the treatment of patients with TS. The authors concluded that given the positive response exhibited by the patient highlighted in this report, further investigation of the effects of nabiximols is proposed on a larger group of patients in a clinical trial setting.
Quezada and Coffman (2018) noted that TS is a neurodevelopmental disorder of unknown etiology characterized by spontaneous, involuntary movements and vocalizations called tics. Once thought to be rare, TS affects 0.3 to 1 % of the population. Tics can cause physical discomfort, emotional distress, social difficulties, and can interfere with education and desired activities. The pharmacologic treatment of TS is particularly challenging, as currently the genetics, neurophysiology, and neuropathology of this disorder are still largely unknown. However, clinical experience gained from treating TS has helped to better understand its pathogenesis and, as a result, derive therapeutic options. The strongest data exist for the anti-psychotic agents, both typical and atypical, although their use is often limited in children and adolescents due to their side-effect profiles. There are agents in a variety of other pharmacologic categories that have evidence for the treatment of TS and whose side-effect profiles are more tolerable than the anti-psychotics; these include clonidine, guanfacine, baclofen, topiramate, botulinum toxin A, tetrabenazine, and deutetrabenazine. A number of new agents are being developed and tested as potential treatments for TS. These include valbenazine, delta-9-tetrahydrocannabidiol (THC), and ecopipam. Additionally, there are agents with insufficient data for efficacy, as well as agents that have been shown to be ineffective. Those without sufficient data for efficacy include clonazepam, ningdong granule, 5-ling granule, omega-3 fatty acids, and n-acetylcysteine. The agents that have been shown to be ineffective include pramipexole and metoclopramide.
Martino and Pringsheim (2018) stated that anti-psychotics (e.g., fluphenazine, haloperidol and pimozide) and alpha adrenergic agonists (e.g., clonidine and guanfacine) remain 1st-line pharmacological interventions for tics, although VMAT-2 inhibitors appear promising.
McKee and colleagues (2021) stated that the use of cannabinoids and cannabinoid-based products (CBPs) as a pharmacological aid to treat psychiatric disorders in adulthood is still poorly understood despite a number of comprehensive general reviews discussing the topic. With a focus on RCT data, this review and meta-analysis aimed to evaluate all current high-quality (Level-1) research that specifically assessed the effectiveness of a CBP on a diagnosed adult psychiatric disorder. The following databases, from their inception to September 2020, were included in the search: Academic Search Premier, PubMed, Ovid Medline, Web of Science, PsycARTICLES, PsycINFO, CINAHL (Nursing and Allied Health), and Scopus. Risk of bias for each study was individually assessed using the revised Cochrane tool. Of the 2,397 papers identified, 31 RCTs met criteria for inclusion: 10 studies focused on treating cannabis use disorder, 6 on schizophrenia, 5 on opioid/tobacco use disorder, 3 on anxiety disorders, 2 on Tourette's disorder, 2 on anorexia nervosa, and 1 trial each for ADHD, OCD, and post-traumatic stress disorder (PTSD). This review found limited evidence for the effectiveness of CBPs to acutely treat a narrow range of psychiatric symptoms. These investigators reported no evidence supporting the mid- to long-range effectiveness of any currently available CBP. In general, quality of the evidence was assessed as low-to-moderate. More importantly, none of the studies discussed in this review presently endorse the use of cannabis flower as a method of treatment for any recognized psychiatric disorder. These researchers stated that larger, hypothesis-driven RCTs are needed before making further therapeutic recommendations.
Ueda and Black (2021) stated that dopamine-depleting agents block the vesicular monoamine transporter type 2 and are used to treat hyperkinetic movement disorders such as chorea, tardive dyskinesia, and tics. Tetrabenazine, a dopamine-depleting agent, was found to be effective in an open-label study of 120 patients with tics. Subsequently, an open-label study of 28 children and adolescents with TS examined valbenazine, which is a purified parent drug of the (+)-α-isomer of tetrabenazine; however, it failed to show statistically significant efficacy. A trial of deutetrabenazine, a deuterated form of tetrabenazine, also failed to show a significant benefit.
Farber and colleagues (2021) noted that significant need exists for effective, well-tolerated pharmacologic treatments for TS. Medications that inhibit vesicular monoamine transporters (i.e., VMAT2 inhibitors) down-regulate pre-synaptic packaging and release of dopamine into the neuronal synapse and are effective in treating hyperkinetic movement disorders such as Huntington's chorea and tardive dyskinesia; therefore, they may be useful in treating TS. These investigators described the clinical program evaluating the safety and effectiveness of valbenazine in the treatment of involuntary tics associated with TS in adult and pediatric subjects. While there was a trend in the 6 completed trials toward greater improvement in valbenazine-treated versus placebo-treated subjects on the primary efficacy endpoint (Yale Global Tic Severity Scale Total Tic Score), this difference did not reach statistical significance. Valbenazine was generally well-tolerated in the studies, and treatment-emergent adverse events (AEs) were consistent with valbenazine studies in TD. The authors concluded that due to the failure to meet the primary endpoint in these trials, further investigation of valbenazine for TS is unlikely. Moreover, these researchers stated that given the need for safe and effective TS therapies and the key role of VMAT2 in modulating dopaminergic activity, it is reasonable for future studies to examine other VMAT2 inhibitors as potential treatments for TS.
Transcranial Direct Current Stimulation
Eapen and colleagues (2017) stated that transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that is being investigated for a variety of neurological and psychiatric conditions. Preliminary evidence suggested that tDCS may be useful in the treatment of TS. These investigators reviewed the literature on the use of tDCS in commonly occurring co-morbid conditions that are relevant to its proposed use in TS. They described the protocol for a double-blind, cross-over, sham-controlled trial of tDCS (Trial ID: ACTRN12615000592549, registered at www.anzctr.org.au) investigating the efficacy, feasibility, safety, and tolerability of tDCS in patients with TS aged 12 years and over. The intervention consists of cathodal tDCS positioned over the supplementary motor area. Patients receive either sham tDCS for 3 weeks followed by 6 weeks of active tDCS (1.4 mA, 18 sessions over 6 weeks), or 6 weeks of active sessions followed by 3 weeks of sham sessions, with follow-up at 3 and 6 months. Pilot findings from 2 participants were presented. There was a reduction in the frequency and intensity of patients' tics and premonitory urges, as well as evidence of improvements in inhibitory function, over the course of treatment. The authors concluded that larger scale studies are needed to determine the maintenance of symptom improvement over time, as well as the long-term consequences of the repetitions of sessions.
Finisguerra and colleagues (2019) noted that in the past several years, there has been a growing interest in the application of different non-invasive brain stimulation (NIBS) techniques to induce neuroplasticity and to modulate cognition and behavior in adults. Very recently, different attempts have been made to induce functional plastic changes also in pediatric populations. More importantly, not only sensorimotor processing, but also higher-level functions have been addressed, with the aim to boost rehabilitation in different neurodevelopmental disorders. However, the safety and effectiveness of using these techniques in pediatric population is still debated. These investigators reviewed the non-invasive brain stimulation studies conducted in pediatric populations using TMS or tDCS. Specifically, the available proofs concerning the efficacy and safety of these techniques on autism spectrum disorder, ADHD, dyslexia, TS, and tic disorders were systematically reviewed and discussed. The authors concluded that the use of NIBS in neurodevelopmental disorders showed the feasibility and promising efficacy of NIBS to support neural plasticity and to reinforce the benefits of cognitive trainings.
Repetitive Transcranial Magnetic Stimulation for Treatment of Tourette Syndrome
Singh and colleagues (2018) examined the effects of low-frequency rTMS (LF-rTMS) in 3 patients with medication-refractory TS and over 3-month follow-up. These investigators also carried out a review of literature on the use of rTMS for the treatment of TS. Three patients with severe, medication-refractory TS and co-morbid OCD in 2 of them, received an open-label trial of rTMS at 1-Hz frequency for 4-week duration. The first 2 cases of TS-OCD showed, on average, around 57 % improvement in YGTSS scores (65 % and 50 %) and 45 % improvement in Yale-Brown Obsessive-compulsive Scale (Y-BOCS) scores; however, the 3rd case of pure-TS showed marginal improvement of 10 % only. The improvement in TS-OCD patients with rTMS treatment was maintained at the end of 3-month follow-up, with an average reduction of about 4 9% (58 % and 40 %) and 36 % observed in YGTSS and Y-BOCS scores, respectively. The authors concluded that the findings of present study supported the use of LF-rTMS to improve tics and OCD symptoms in patients with severe, medication-refractory TS-OCD. These researchers stated that the lack of treatment effect observed in pure-TS patient may assist in the identification of the TS population responsive to inhibition of the supplementary motor area in the future studies. They stated that in future, larger, double-blind, randomized placebo-controlled studies with higher number (total number of rTMS sessions and pulses delivered) of rTMS stimulation treatments and long-term follow-up periods should be done to confirm the findings of the present study and to determine the sustainability of the effects of rTMS and to explore the need of maintenance rTMS protocols for continuing the beneficial effects of rTMS treatment.
Theta Burst Stimulation
Dyke and colleagues (2022) TS is a neurodevelopmental condition characterized by tics, which are stereotyped movements and/or vocalizations. Tics often cause difficulties in daily life and many patients with TS express a desire to reduce and/or gain control over them. No singular effective treatment exists for TS, and while pharmacological and behavioral interventions can be effective, the results are variable, and issues relating to access, availability and side effects can be barriers to treatment. Consequently, over the last 10 years, there has been increasing interest into the potential benefits of non-invasive brain stimulation (NIBS) approaches. In a systematic review, these investigators highlighted work examining NIBS as a potential treatment for TS. On balance, the results tentatively suggested that multiple sessions of stimulation applied over the supplementary motor area (SMA) may help to reduce tics. However, a number of methodological and theoretical issues limited the strength of this conclusion, with the most problematic being the lack of large-scale, sham-controlled studies. These researchers stated that currently, the most commonly used TMS method for therapeutic neuromodulation in patients with TS is rTMS, including a patterned version of this known as theta burst stimulation (TBS). TBS is a patterned form of rTMS, in which bursts of 3 TMS pulses at 30- or 50-Hz are delivered at a rate of 5 Hz. This patterned stimulation can be delivered either in a continuous (cTBS) or intermittent (iTBS) fashion. The authors concluded that the evidence to-date suggests that TMS and tDCS approaches may be helpful in reducing tics, yet there remains a substantial amount of further work needed for these approaches to reach a convincing level of supporting evidence. Complex interactions between clinical symptoms, cortical states, and the NIBS parameters require serious consideration, and the field urgently needs additional studies to address a number of issues.
Neuroimaging
Hienert and colleagues (2019) stated that despite intense research, the underlying mechanisms and the etiology of TS remain unknown. Data from molecular imaging studies targeting the dopamine system in Tourette patients are inconclusive. For a better understanding of the striatal dopamine function in adult dopamine-antagonist-free patients these investigators performed a systematic review in August 2017 identifying 49 PET and single-photon emission computed tomography (SPECT) studies on the topic of TS. A total of 8 studies appraised the dopamine transporter (DAT) with 111 Tourette patients and 93 healthy controls, and could be included in a meta-analytic approach. These researchers found a significantly increased striatal DAT binding in Tourette patients (Hedges' g = 0.49; 95 % CI: 0.01 to 0.98), although this effect did not remain significant after correcting for age differences between cohorts. A second meta-analysis was performed for the striatal dopamine receptor including 8 studies with a total of 72 Tourette patients and 71 controls. This analysis revealed a non-significant trend toward lower dopamine 2/3 receptor binding in striatum of Tourette patients. Other analyses regarding study population characteristics in both the DAT and receptor meta-analysis did not show any meaningful results. The authors concluded that these findings indicated that dopaminergic alterations in TS are likely; and therefore these data would be in line with the current pathophysiological hypotheses of a dysfunction in the dopamine system, e.g., the hypothesis of tonic-phasic dysfunction. However, they stated that these analyses suffered from low effect sizes probably due to the heterogeneity of TS and highlighted the need for large-scaled, systematic, longitudinal neuroimaging studies with well-matched control groups to understand the pathophysiology of TS and thereby make the development of a curative therapy possible.
Cognitive and Motor Event-Related Potentials in Tourette Syndrome
Morand-Beaulieu and Lavoie (2018) noted that TS patients face various cognitive and motor impairments. Event-related potentials (ERP) constitute an effective way to examine the neural correlates of those functional impairments. Various components have been assessed among TS patients, with a wide variety of paradigms. In a systematic review, these investigators evaluated the portrait of ERP components in TS patients, and examined the factors leading to discrepancies across studies. They carried out a literature search in Embase, PsycINFO, PubMed, and Web of Science, to identify studies that conducted ERP experiments among TS patients. Of the 372 unique records identified, 47 met inclusion criteria and were included in this systematic review. Various ERP particularities were reported among included studies. Many discrepancies exist, but impairments in motor-related potentials and contingent negative variation appeared constant across studies. Divergent findings point toward a possibly reduced P3b during oddball tasks. The authors concluded that ERPs offered an insightful examination into the cognitive and motor functions of TS patients. Moreover, these researchers stated that future studies should always control for confounding factors such as co-morbidity, age, or medication status. They noted that this was the first systematic review of ERP in TS patients; motor-related and slow cortical potentials could constitute electrophysiological markers of TS.
Pallidal Deep Brain Stimulation Combined with Capsulotomy for the Treatment of Tourette's Syndrome
Zhang and colleagues (2019) stated that a current challenge is finding a safe and effective treatment for severely disabled patients with TS and co-morbid psychiatric disorders, in whom conventional treatments have failed. These researchers examined the utility of globus pallidus internus DBS (GPi-DBS) combined with bilateral anterior capsulotomy in treating these clinically challenging patients. These researchers conducted a retrospective review of the clinical history and outcomes of 10 severely disabled patients with treatment-refractory TS and a psychiatric co-morbidity, who had undergone GPi-DBS combined with bilateral anterior capsulotomy in their hospital. At the time of surgery, patients presented mainly with OCD and affective disorders. Clinical outcome assessments of tic and psychiatric symptoms, as well as of general adaptive functioning and QOL, were performed at the time of surgery and at 6, 12, and between 24 and 96 months post-surgery. After surgery, all patients showed significant progressive improvements in tic and psychiatric symptoms, along with improvements in general adaptive functioning and QOL. Tic alleviation reached 64 % at 12 months and 77 % at the last follow-up on the YGTSS. At the final follow-up, patients had functionally recovered and displayed no or only mild tic and psychiatric symptoms. All patients tolerated treatment reasonably well, with no SAEs. The authors concluded that GPi-DBS combined with bilateral anterior capsulotomy appeared to offer major clinical benefits to severely disabled patients with otherwise treatment-refractory TS and psychiatric co-morbidities. These preliminary findings need to be validated by well-designed studies.
Prefrontal Cortical Electrical Stimulation for the Treatment of Tourette's Syndrome
Perani and colleagues (2018) stated that the benefits of neurosurgery in TS are still incompletely understood. Prefrontal cortical electrical stimulation offers a less invasive alternative to DBS. These researchers performed a pilot study on the safety and efficacy of prefrontal cortical bilateral electrical stimulation in TS using clinical and brain metabolic assessments. A total of 4 adult TS patients underwent tic assessment using the YGTSS and the RVRS at baseline and 1, 3, 6, and 12-months following implantation; whereas FDG-PET scans were acquired at baseline and after 6 and 12 months. Tic clinical scores were improved at 6 months following implantation, meanwhile they showed a tendency to re-emerge at the 12-month follow-up. There was a correlation between FDG-PET and tics, mainly consisting in a reduction of baseline brain hyper-metabolism, which paralleled tic score reduction. The authors concluded that prefrontal cortical electrical stimulation in TS was safe and yielded a modulation of tics, paralleled by FDG-PET metabolic modulation. The findings of this proof-of-concept study need to be validated by well-designed studies.
Baclofen
Pringsheim and colleagues (2019) systematically examined the efficacy of treatments for tics and the risks associated with their use. This project followed the methodologies outlined in the 2011 edition of the American Academy of Neurology (AAN)'s guideline development process manual. These researchers included systematic reviews and RCTs on the treatment of tics that included at least 20 participants (10 participants if a cross-over trial), except for neurostimulation trials, for which no minimum sample size was required. To obtain additional information on drug safety, these investigators included cohort studies or case series that specifically evaluated adverse drug effects in individuals with tics. There was high confidence that the comprehensive behavioral intervention for tics was more likely than psychoeducation and supportive therapy to reduce tics. There was moderate confidence that haloperidol, risperidone, aripiprazole, tiapride, clonidine, onabotulinumtoxinA injections, 5-ling granule, Ningdong granule, and DBS of the globus pallidus were probably more likely than placebo to reduce tics. There was low confidence that pimozide, ziprasidone, metoclopramide, guanfacine, topiramate, and tetrahydrocannabinol were possibly more likely than placebo to reduce tics. Evidence of harm associated with various treatments was also demonstrated, including weight gain, drug-induced movement disorders, elevated prolactin levels, sedation, and effects on heart rate, blood pressure, and ECGs. There is insufficient evidence to determine whether people with tics receiving the following interventions are more or less likely than those receiving placebo to have reduced tic severity: baclofen, IVIG, nicotine patch added to haloperidol, ondansetron, and pramipexole.
Cranial Electrotherapy Stimulation
In a randomized, double-blind, sham-controlled trial, Wu and colleagues (2020) examined the safety and efficacy of cranial electrotherapy stimulation (CES) as an add-on treatment for TD. This trial was carried out at an out-patient, single-center academic setting. A total of 62 patients aged 6 to 17 years with TD and lack of clinical response to 4 weeks' pharmacotherapy were enrolled. Patients were divided randomly into 2 groups and given 4 weeks' treatment, including 30-min sessions of active CES (500 μA to 2 mA) or sham CES (lower than 100 μA) per day for 40 days on weekdays. Change in YGTSS, CGI-severity of illness-severity (CGI-S) and Hamilton Anxiety Scale-14 items (HAMA-14) were performed at baseline, week 2, week 4; AEs were also evaluated. A total of 53 patients (34 males and 9 females) completed the trial, including 29 in the active CES group and 24 in the sham CES group. Both groups showed clinical improvement in tic severities compared to baseline respectively at week 4. Participants receiving active CES showed a reduction of 31.66 % in YGTSS score, compared with 23.96 % in participants in sham CES group, resulting in no significant difference between the 2 groups (t = 1.54, p = 0.13). The authors concluded that 4-week's treatment of CES for children and adolescents with TD was safe and effective, however, the improvement for tic severity may be related to placebo effect. These researchers stated that these findings were promising and encouraged further trials to examine the efficacy of CES in a large sample.
Neurofeedback
Sukhodolsky and colleagues (2020) stated that activity in the supplementary motor area (SMA) has been associated with tics in TS. In a randomized, double-blind, sham-controlled, cross-over trial, these researchers examined a novel intervention -- real-time functional magnetic resonance imaging (fMRI) neurofeedback from the SMA -- for reduction of tics in adolescents with TS. A total of 21 adolescents with TS were enrolled in this study involving 2 sessions of neurofeedback from their SMA. The primary outcome measure of tic severity was the YGTSS administered by an independent evaluator before and after each arm. The secondary outcome was control over the SMA assessed in neuroimaging scans, in which subjects were cued to increase/decrease activity in SMA without receiving neurofeedback. All 21 subjects completed both arms of the study and all assessments. Participants had significantly greater reduction of tics on the YGTSS after real neurofeedback as compared with the sham control (p < 0.05). Mean YGTSS Total Tic score decreased from 25.2 ± 4.6 at baseline to 19.9 ± 5.7 at end-point in the neurofeedback condition and from 24.8 ± 8.1 to 23.3 ± 8.5 in the sham control condition. The 3.8-point difference was clinically meaningful and corresponds to an effect size of 0.59. However, there were no differences in changes on the secondary measure of control over the SMA. The authors concluded that this 1st RCT of real-time fMRI neurofeedback in adolescents with TS suggested that this neurofeedback intervention may be helpful for improving tic symptoms. However, no effects were found in terms of change in control over the SMA, the hypothesized mechanism of action.
Relaxation Therapy
Tilling and Cavanna (2020) noted that TS is a neurodevelopmental condition characterized by the presence of multiple motor and phonic tics, often associated with co-morbid behavioral problems. Tics can be modulated by environmental factors and are characteristically exacerbated by psychological stress, among other factors. This observation has led to the development of specific behavioral treatment strategies, including relaxation therapy. In a systematic review, these researchers examined the efficacy of relaxation therapy to control or reduce tic symptoms in patients with TS. They conducted a systematic literature review of original studies on the major scientific databases, including Medline, Embase, and PsycInfo, according to the standards outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Outcomes measures included both tic severity and tic frequency. The literature search identified 3 controlled trials, with a total number of 40 participants (range of 6 to 18 participants). In all 3 studies, relaxation therapy decreased the severity and/or the frequency of tic symptoms. However, the only trial comparing relaxation therapy to 2 other behavioral techniques found relaxation therapy to be the least effective intervention, as it reduced the number of tics by 32 % compared to 44 % with self-monitoring and 55 % with habit reversal. The authors concluded that the findings of this systematic literature review provided initial evidence for the use of relaxation therapy as a behavioral treatment intervention for tics in patients with TS. Moreover, these researchers stated that caution is needed in the interpretation of these findings, because the reviewed trials had small sample sizes and there was high heterogeneity across the study protocols. They stated that as the available literature is limited, further research is needed to confirm these preliminary findings and reach more accurate conclusions. Specifically, it is still unclear how relaxation therapy compares to other behavioral treatment interventions for tic control, as well as its exact role within multi-component behavioral interventions for tic control such as the Comprehensive Behavioral Intervention for Tics.
MicroRNAs (miRNAs) as a Biomarker for Tourette Syndrome
Paul and colleagues (2020) noted that microRNAs (miRNAs) are short, endogenous, non-coding RNAs that regulate gene expression via post-transcriptional mechanisms through degradation or inhibition of specific mRNAs targets. In recent years, many studies have demonstrated the relevance of miRNAs in human psychopathology. In this review, these investigators discussed neuropsychiatric disorders with moderate-to-high prevalence among children and adolescents such as autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), dyslexia, epilepsy, schizophrenia and TS focusing on the functional consequence of altered miRNA expression during the development of such diseases. The insight regarding the roles that miRNAs play in central nervous systems (CNS) development such as cell proliferation and differentiation, synaptogenesis, synaptic plasticity, and apoptosis might be the key to develop novel biomarkers for diagnosis and prognosis of these disorders, as well as the finding of new targets for drug development for therapeutic approaches.
Juvale and Has (2021) stated that neurodevelopmental disorders are defined as a set of abnormal brain developmental conditions marked by the early childhood onset of cognitive, behavioral, and functional deficits leading to memory and learning problems, emotional instability, and impulsivity. These researchers noted that ASD, ADHD, TS, fragile X syndrome, and Down's syndrome are a few known examples of neurodevelopmental disorders. Although they are relatively common in both developed and developing countries, very little is currently known regarding their underlying molecular mechanisms. Both genetic and environmental factors are known to increase the risk of neurodevelopmental disorders. Current diagnostic and screening tests for neurodevelopmental disorders are unreliable; thus, individuals with neurodevelopmental disorders are often diagnosed in the later stages. This negatively impacts their prognosis and QOL, prompting the need for a better diagnostic biomarker. These researchers stated that recent studies on miRNAs and their altered regulation in diseases have shed some light on the possible role they could play in the development of neurodevelopmental disorders. The authors discussed the current understanding of the role that microRNAs play in neurodevelopmental disorders with the hope of using them as potential biomarkers in the future.
Furthermore, an UpToDate review on “Tourette syndrome: Pathogenesis, clinical features, and diagnosis” (Jankovic, 2021) does not mention microRNA as a biomarker for TS.
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