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Background
Tinnitus is defined as the aberrant perception of noise or sound without any external stimulation. It may be unilateral or bilateral and has equal prevalence in women and men and is most prevalent between the ages of 40 and 70. Occasionally, tinnitus can also occur in children. Periodic bouts of mild, high-pitched tinnitus lasting for several minutes are common in normal-hearing individuals. Severe and persistent tinnitus can interfere with sleep and the ability to concentrate, causing great psychological distress. In extreme cases, patients with severe chronic tinnitus may consider suicide. Tinnitus can be classified into two types: (i) subjective tinnitus, and (ii) objective tinnitus.
Subjective tinnitus, which is more common, is audible only to the patient. It may arise from some types of electrophysiological disturbance anywhere in the auditory system -- the external ear canal, tympanic membrane, ossicles, cochlea, auditory nerve, brainstem or cerebral cortex. The underlying causes of subjective tinnitus include otological (presbycusis, noise-induced hearing loss, Meniere's disease, or chronic otitis media), metabolic (diabetes, thyroid diseases, hyperlipidemia, or zinc deficiency/vitamin deficiency), pharmacological (aspirin compounds, non-steroidal anti-inflammatory drugs, caffeine, nicotine, aminoglycosides, or antidepressants), neurological (whiplash, skull fracture/closed head trauma, multiple sclerosis, or following meningitis), psychological (depression or anxiety), as well as infectious and neoplastic (syphilis, acoustic neuroma, autoimmune diseases, or acquired immune deficiency syndrome) disorders.
Objective tinnitus, the less common type of tinnitus, usually refers to noises that can be heard by an examiner. The physician must put his/her ear against the patient's ear or use a stethoscope against the patient's external auditory canal. Objective tinnitus usually has a vascular (arteriovenous malformations/shunts, arterial bruits, hypertension, arteriosclerosis, venous hums, or aneurysms) or mechanical (Eutaschian tube dysfunction, temporomandibular joint disease, palatal myoclonus, or idiopathic stapedal muscle spasm) origin (Schuler and Schleuring, 1994; Seidman and Jacobson, 1996).
The management of patients with tinnitus often depends on the severity of the condition. If the patient's activities of daily living are not affected by tinnitus, treatment options include counseling, reassurance, and/or behavioral and dietary modifications (avoidance of excessive noise, nicotine, salt, and caffeine). All medications should also be evaluated to eliminate ototoxic drugs. Currently, the medications for patients with severe tinnitus include amitriptyline (Elavil), alprazolam (Xanax), diazepam (Valium), and clonazepam (Klonopin); however, none of these drugs has been approved by the Food and Drug Administration for the specific treatment of tinnitus.
Electrical Stimulation:
Another therapeutic modality is electrical stimulation (ES). In a review on tinnitus, Siedman and Jacobson (1996) indicated that ES is a possible treatment modality for patients with severe tinnitus. Hatton et al (1960) reported that only anodal (positive electrode) stimulation produced the suppressive effect. In general, ES is provided through electrodes in the vicinity of the ear. The exact mechanism(s) by which ES suppresses/reduces tinnitus is unclear. However, it has been postulated that positive electrical currents produce a hyperpolarization of nerve fibers, which inhibit and reduce spontaneous discharge rates (Portmann et al, 1983).
Hatton et al (1960) observed that the intensity of tinnitus was reduced in 15 (45.5 %) of 33 patients with ES. Chouard et al (1981) reported that 30 (47 %) of 64 patients achieved success (as determined by reduced intensity that lasted for a few days to more than 1 week) following electrotherapy. None of the 12 patients who received placebo stimulation attained relief. The authors stated that if a patient failed to achieve improvement after 2 to 3 sessions, it is unlikely that this form of therapy will be successful.
Engelberg and Bauer (1985) performed two experiments to examine the effects of transcutaneous electrical stimulation (TENS) on tinnitus. Experiment 1 had 10 subjects (18 ears) and improvement (defined as either a complete remission or a decrease in the frequency of tinnitus) was seen in 6 of them with tinnitus being eliminated in 3 ears. Experiment 2 employed a single-blind study design with 20 patients (experimental group, n = 10, 17 ears; control group, n = 10, 15 ears). It was found that 9 of 10 patients with 15 (88.2 %) of 17 ears reported improvement following stimulation. These changes lasted from 20 minutes to at least 6 months. On the other hand, only 1 patient (1 ear) in the control group improved (a 13 % decrease in frequency of tinnitus).
Steenerson and Cronin (1996) reported their findings of 246 patients with severe tinnitus of various etiologies treated with ES (a total of 6 to 10 sessions). One hundred and thirty patients (53 %) reported significant benefit (an improvement of at least 2 points in a 1 to 10 subjective rating scale) with 32 patients (13 %) having complete suppression of their tinnitus. At 3-month follow-up, 72 % had continuous benefit.
In a subsequent report, Steenereson and Cronin (1999) reported their findings in 500 patients with tinnitus who were treated with probe electrical stimulation. The authors reported that 53% of patients showed decreases in their tinnitus as measured by a subjective rating scale. At 3-month follow-up, 72% had no loss of benefit.
Rahko and Kotti (1997) treated 26 patients with transcutaneous nervous stimulation (TNS) for tinnitus. Except for 3 normal hearing patients, all had cochlear hearing losses. The authors found that tinnitus disappeared in none of the patients, but diminished in 7 patients, versus diminution of tinnitus in 3 in 24 nontreated controls.
In a study that evaluated the effects of psychological factors on the outcome of TENS for patients with chronic tinnitus (n = 27), Collet et al (1987) found that the 15 patients (55.6 %) who did not improve showed higher pre-treatment scores of depression, psychasthenia, and schizophrenia. These findings indicated that patients having psychiatric problems such as those mentioned above are unlikely to benefit from treatment.
According to available literature, transcutaneous electrical stimulation for tinnitus is contraindicated in persons with the following conditions:
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Persons taking medications for other diseases/conditions known to have a side effect of tinnitus, such as aspirin, Vasotec (enalapril maleate), etc.; or
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Women who are pregnant; or
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Persons with cardiac pacemakers, implanted stapes prostheses or other implanted devices, which may be affected by electrical signals; or
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Persons with active ear disease; or
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Persons with psychiatric problems such as schizophrenia, depression, hysteria, or hypochondria.
Masking Instruments:
Tinnitus masking instruments such as maskers, hearing aids, and tinnitus devices (combination of hearing aid and tinnitus masker) have been used for alleviating symptoms associated with tinnitus. However, the effectiveness of these instruments for treating tinnitus has not been established. These devices are all worn behind, or in either the same or opposite ear affected by tinnitus. Tinnitus maskers generate a grossly broad-band high-energy noise, which most patients find an excessive noise intrusion that is unacceptable and intolerable.
A review of 69 randomized clinical trials of therapies for tinnitus (Dobie, 1999) concluded that no treatment (pharmacotherapy, psychotherapy, and various non-drug treatments including masking) could yet be considered established in terms of providing reproducible long-term benefits, in excess of placebo effects. A more recently published evidence review (Waddell and Canter, 2002) concluded that there is “insufficient evidence about the effects of tinnitus masking devices in people with chronic tinnitus”. The authors also concluded that there was insufficient evidence of the effectiveness of acupuncture, hypnosis, low power laser, and electromagnetic stimulation and ear canal magnets in treating tinnitus. Regarding the effectiveness of psychotherapy for tinnitus, the review concluded “that there is limited evidence in two similar systematic reviews that psychotherapy may improve symptom scores of people with chronic tinnitus, but weakness of methods used in the reviews, and in the studies they included, means that the effects of psychotherapy remain unclear”.
A systematic review of the evidence for tinnitus treatments by BMJ Clinical Evidence concluded that tinnitus masking devices and hearing aids are of "unknown effectiveness" (Savage, et al., 2006).
The Centers for Medicare and Medicaid Services (CMS, 2006) has concluded: “Tinnitus masking is considered an experimental therapy at this time because of a lack of controlled clinical trials demonstrating effectiveness and the unstudied possibility of serious toxicity in the form of noise induced hearing loss.”
Ear Canal Magnets and Electromagnetic Stimulation:
A systematic evidence review published in BMJ Clinical Evidence (Savage, et al., 2006) concluded that the effectiveness of ear canal magnets and electromagnetic stimulation for tinnitus are unknown.
The systematic evidence review identified two small randomized, controlled clinical trials comparing electromagnetic stimulation to placebo. The first trial (n = 58) found that 15 minutes per day of electromagnetic stimulation significantly increased the proportion of people who had subjective improvements in tinnitus compared to placebo after one week (Roland, et al., 1993). Based upon subjective responses assessed by a four-point questionnaire, 14 of 31 subjects assigned to electromagnetic stimulation improved compared to 2 of 23 subjects assigned to placebo (p = 0.0013). The systematic review noted that 4 subjects withdrew from the trial, and that the analysis was not by intention to treat. A second randomized controlled clinical trial (n = 20) used a crossover design and did not report results before the crossover (Dobie, et al., 1986). The crossover trial found similar effects between electromagnetic stimulation and a placebo device in reducing tinnitus severity. Severity, measured on a scale of 0-7, was reported as less severe in 2 of 20 subjects with the active device versus three of 20 subjects with a placebo device.
The systematic evidence review found one randomized controlled clinical trial (n = 49) that found similar effects between a simple ear-canal magnet and placebo (similar unmagnetized material) in tinnitus symptoms after 4 weeks' treatment (Coles, et al., 1991). Symptom improvement was reported in 7 of 26 persons with the magnet compared to 4 of 23 persons with placebo.
Tinnitus Retraining Therapy:
Tinnitus retraining therapy (TRT) is a neurophysiological approach centering on behavioral retraining of the associations induced by perception of tinnitus. It uses devices similar to tinnitus maskers. These devices, known as white noise generators, produce white noise, and are used over a period of several months to help patients in their habituation of tinnitus. Measurement of the tinnitus match is performed after an audiogram. The patient is asked to identify which of the tones of the audiometer match the tone of the ringing of his or her tinnitus. Examples of measures quantified include pitch, loudness and minimal masking level of the tinnitus. As mentioned, these parameters are then used for tinnitus retraining and for selecting devices, which can produce “white noise” to counterbalance and reduce or eliminate the tinnitus. There are several factors that influence the frequency spectrum of the perceived noise such that the perception of white noise from a white noise generator is unlikely. These factors include (i) the actual spectrum of the emitted noise, (ii) the ear canal resonance of the patient, and (iii) the hearing sensitivity of the patient. Furthermore, a study stated that methodological limitations of the research published to date preclude any claims about the efficacy of TRT at the present time (Wilson et al, 1998). A technology assessment prepared for the Wessex Institute for Health Research and Development (Leal and Milne, 1998) concluded that the available case series are inadequate, owing to problems of methodology, and that there is no evidence to suggest that TRT is effective in the treatment of debilitating tinnitus in adult patients.
Kroener-Herwig et al (2000) stated that there is no published study evaluating TRT using a randomized group design even though this is the only design able to give valid information on the empirical status of a therapy. They concluded that the praise of TRT as the most promising therapy for chronic tinnitus can only be regarded as premature, and the claim of its effectiveness by its advocates await scientific corroboration. Randomized, controlled clinical studies that include no-treatment and placebo groups are needed to ascertain the effectiveness of TRT in the management of patients with tinnitus.
An assessment by the Washington Department of Labor and Industries Office of the Medical Director (Wang, 2004) concluded that “[d]ue to the lack of prospective trials with comparison groups, the efficacy of TRT for subjective tinnitus has not been established. Therefore, TRT is considered investigational and controversial.”
A systematic review of the evidence for tinnitus treatments by BMJ Clinical Evidence concluded that tinnitus training therapy is of "unknown effectiveness" (Savage, et al., 2006).
Transcranial Magnetic Stimulation:
Clinical, neurophysiological and neuroimaging data suggest that chronic tinnitus resembles neuropsychiatric syndromes characterized by focal brain activation. Low-frequency repetitive transcranial magnetic stimulation (rTMS) has been proposed as a method in treating brain hyperexcitability disorders by reducing cortical excitability. Kleinjung et al (2005) examined the effects of rTMS on patients with chronic tinnitus (n = 14). Increased metabolic activation in the auditory cortex was verified in all patients. After 5 days of rTMS, a highly significant improvement of the tinnitus score was found whereas the sham treatment did not show any significant changes. The treatment outcome after 6 months still demonstrated significant reduction of tinnitus score. The authors concluded that these preliminary results showed that neuro-navigated rTMS offers new possibilities in the understanding and treatment of chronic tinnitus. The findings of this study need to be verified by further investigation with larger sample size and long follow-up.
Pridmore et al (2006) examined the literature and considered the potential for TMS as a treatment for patients with tinnitus. These researchers noted that a small number of studies have suggested that TMS may be effective in the treatment of tinnitus. There is a good theoretical basis and early research evidence suggesting that TMS may have treatment potential in tinnitus. Moreover, they stated that further, larger studies are necessary to ascertain the effectiveness of this approach.
In a randomized, placebo-controlled (sham stimulation) cross-over pilot study, Smith et al (2007) evaluated the effectiveness of neuro-navigated rTMS and its effects on attentional deficits and cortical asymmetry in 4 patients with chronic tinnitus using objective and subjective measures and employing an optimization technique refined in their laboratory. Patients received 5 consecutive days of active, low-frequency rTMS or sham treatment (using a 45-degree coil-tilt method) before crossing over. Subjective tinnitus was assessed at baseline, after each treatment, and 4 weeks later. Positron emission tomography/computed tomography (PET/CT) scans were obtained at baseline and immediately after active treatment to examine change in cortical asymmetry. Attentional vigilance was assessed at baseline and after each treatment using a simple reaction time test. All patients had a response to active (but not sham) rTMS, as indicated by their best tinnitus ratings; however, tinnitus returned in all patients by 4 weeks after active treatment. All patients had reduced cortical activity visualized on PET immediately after active rTMS. Mean reaction time improved (p < 0.05) after active but not sham rTMS. The authors concluded that rTMS is a promising treatment modality that can transiently diminish tinnitus in some individuals, but more studies are needed to determine the optimal techniques needed to achieve a lasting response. It is unclear if the improved reaction times were caused by tinnitus reduction or a general effect of rTMS. PET/CT scans immediately after treatment suggest that improvement may be related to reduction of cortical asymmetry associated with tinnitus.
Khedr et al (2008) compared the effect of different frequencies of rTMS (1 Hz, 10 Hz, 25 Hz and sham (occipital, 1 Hz)), given daily over the left temporo-parietal cortex for 2 weeks, on 66 patients with chronic tinnitus randomly divided into four treatment groups. Patients were assessed using the Tinnitus Handicap Inventory (THI), self-ratings of symptoms and audiometric measures of residual inhibition before, immediately after 2 weeks' treatment and monthly thereafter for 4 consecutive months. There were no significant differences in basal measures between the four groups of patients. A 2-factor ANOVA revealed a significant "rTMS" x "time" interaction for all measures. This was because real rTMS produced greater improvement than sham. However, there was no significant difference between the responses to different frequencies of rTMS. The response to rTMS depended on the duration of tinnitus: patients who had tinnitus for the longest period of time were the least likely to respond to treatment. The authors concluded that daily sessions of rTMS over the temporo-parietal cortex may be a useful potential treatment for tinnitus.
In a pilot study, Lee and colleagues (2008) examined the effectiveness of rTMS in veterans with debilitating tinnitus. A total of 8 patients received 5 consecutive days of rTMS (0.5 Hz, 20 minutes) to the left temporo-parietal area. Outcome was measured by means of THI before sessions 1 and 3 and after session 5. Patient 1's THI decreased from 40 to 34 to 26, patient 4 reported a subjective improvement, patient 8 withdrew, and the remaining 5 patients reported no improvement. Side effects included temporary soreness, restlessness, and photophobia. The authors concluded that with these current parameters, rTMS did not improve tinnitus in veterans.
Transmeatal Laser Irradiation:
In a prospective, randomized, double-blinded, controlled study, Nakashima, et al. (2002) assessed the effectiveness of 60-mW laser irradiation in the treatment of tinnitus. A total of 68 ears in 45 patients with disabling unilateral or bilateral tinnitus were included in this trial. The active or placebo laser treatment was administered transmeatally once a week for 6 minutes. Laser irradiation was performed four times during a 4-week period. A questionnaire was administered to evaluate the loudness, duration, quality, and annoyance of tinnitus before and after irradiation. The loudness and pitch match for tinnitus were obtained, and distortion product otoacoustic emissions were also examined. No significant difference was observed between the active and placebo laser groups with regard to outcome of loudness, duration, quality, and annoyance of tinnitus. In 1 patient who received active laser treatment, acute hearing deterioration occurred after the third irradiation. These investigators concluded that transmeatal low-power laser irradiation with 60 mW is ineffective for the treatment of tinnitus.
Tauber, et al. (2003) presented their findings of a feasibility study on the use of a laser application system in patients with chronic cochlear tinnitus and sensorineural hearing loss (n = 35). The laser TCL-system, consisting of 4 diode lasers (lambda = 635 - 830 nm) was developed on the basis of dosimetric data from a former light-dosimetric study. The chronic symptoms persisted after standard therapeutic procedures for at least 6 months, while retrocochlear or middle-ear pathologies have been ruled out. The patients were randomised and received 5 single-diode laser treatments (lambda = 635 nm, 7.8 mW cw, n = 17 and lambda = 830 nm, 20 mW cw, n = 18) with a space irradiation of 4 J/cm2 site of maximal cochlear injury. For evaluation of laser-induced effects complete otolaryngological examinations with audiometry, tinnitus masking and matching, and a tinnitus-self-assessment were performed before, during, and after the laser-irradiation. The first clinical use of the TCL-system has been well-tolerated without side-effects and produced no observable damage to the external, middle or inner ear. Changes of tinnitus loudness and tinnitus matching have been described. After a follow-up period of 6 months, tinnitus loudness was attenuated in 13 of 35 irradiated patients, while 2 of 35 patients reported their tinnitus as totally absent. Hearing threshold levels and middle ear function remained unchanged. These researchers stated that further investigations by large double-blind placebo-controlled studies are mandatory for clinical evaluation of the presented TCL-system and its therapeutic effectiveness in acute and chronic cochlear dysfunction.
A systematic review of randomized controlled clinical trials of low powered laser treatments for tinnitus found no statistically significant difference between laser and placebo (Meehan, et al., 2004).
Gungor et al (2008) assessed the effectiveness of laser irradiation in the treatment of chronic tinnitus. This study included 66 ears in 45 patients with chronic unilateral or bilateral tinnitus. A 5 mW laser with a wavelength of 650 nm, or placebo laser, was applied transmeatally for 15 minutes, once-daily for a week. A questionnaire was administered which asked patients to score their symptoms on a 5-point scale, before and 2 weeks after laser irradiation. A decrease of 1 scale point, regarding the loudness, duration and degree of annoyance of tinnitus, was deemed as improvement. The loudness, duration and degree of annoyance of tinnitus were improved, respectively, in up to 48.8, 57.7 and 55.5 % of the patients in the active laser group. No significant improvement was observed in the placebo laser group. The authors concluded that transmeatal, low power (5 mW) laser irradiation was found to be useful for the treatment of chronic tinnitus. The findings of this study need to be validated by larger studies with longer follow-up.
Hyperbaric Oxygen Therapy:
In a Cochrane review on the use of hyperbaric oxygen therapy (HBOT) for the treatment of idiopathic sudden sensorineural hearing loss (ISSHL) and tinnitus, Bennett, et al. (2005) stated that HBOT improved hearing, but the clinical significance of the level of improvement is unclear. Routine application of HBOT to patients with ISSHL is not justified by this review. These investigators noted that more research is needed.
A systematic evidence review of tinnitus treatments by BMJ Clinical Evidence concluded that hyperbaric oxygen is of "unknown effectiveness" (Savage, et al, 2006).
Sequential Phase Shift Sound Cancellation Treatment:
Sequential phase shift sound cancellation is a novel treatment for predominant-tone tinnitus. It entails the use of a phase-shift sound cancellation protocol in which a patient’s tinnitus is first identified as to frequency and amplitude. Then, a signal, 6 degrees out-of-phase with the identified tinnitus signal, is fed sequentially (6 degrees, 12 degrees, etc.) into the patient’s headphones for 30 seconds each for 30 minutes, or until 360 degrees is achieved. Available evidence on the effectiveness of this approach has mainly been in abstract forms (Noik, 2005; Choy and Kaminow, 2005; Lipman et al, 2006). The only published full-length paper on this subject is by Lipman and Lipman (2007) who assessed phase shift treatment for predominant tone tinnitus in a prospective, single-blinded, cross-over study. A total of 61 patients participated in 2 weeks of control and 2 weeks of phase shift treatment. Outcome measures included frequency and intensity matching, pre- and post-treatment tinnitus handicap inventory (THI) scores, and patient diaries. Initial volume comparisons showed a strong relationship between treatment and decrease in tinnitus intensity, with 57 % of patients achieving successful treatment. Thirty-seven percent decreased by one THI grade, 5 % by two. Utilizing patient diaries, 42 % of patients reported periods of complete residual inhibition (CRI) ranging from 1 hour to 7 days (average of 2 days). No periods of CRI were reported in control weeks. The authors concluded that phase shift treatment significantly benefited the majority of patients. These findings suggested that this device may be a valuable tool. They noted that further long-term studies with home therapy are needed.
Thus, there is currently insufficient evidence to support the use of sequential phase shift sound cancellation treatment for tinnitus.
Neuromonics Tinnitus Treatment:
The Neuromonics Tinnitus Treatment (NTT) combines the use acoustic stimulation with a structured program of counseling and support by a clinician specifically trained in tinnitus rehabilitation. The acoustic component has been designed to provide stimulation to auditory pathways deprived by hearing loss, engage with the limbic system, and allow intermittent, momentary tinnitus perception within a pleasant and relaxing stimulus, thereby facilitating desensitization to the tinnitus signal. Davis and colleagues (2007) examined the effectiveness of NTT, when enhanced with various modifications since previously reported trials and tested the relative clinical effectiveness of two variations of the approach. In the first, intermittent tinnitus perception was facilitated throughout treatment via the use of a stimulus in which intensity peaks allowed the subjects' tinnitus perception to be completely covered up, whereas in the intensity troughs their tinnitus was briefly discernible. In the second, subjects experienced little tinnitus perception while listening to the treatment for the first 2 months, then experienced intermittent perception. A total of 35 subjects with a predominantly moderate-to-severe level of tinnitus-related distress before treatment were randomly allocated into one of two treatment groups, corresponding to the 2 stage-based variations of the NTT. Subjects were provided with a high-fidelity personal sound player with earphones and an acoustic stimulus that had been spectrally modified according to their individual audiometric profile. They were instructed to use the acoustic stimulus for at least 2 hours per day, particularly at those times when their tinnitus was usually disturbing. Each group had equal amounts of clinician time for education, monitoring, and support. At 2, 4, 6, and 12 months after commencing treatment, both groups displayed clinically and statistically significant improvements in tinnitus distress, awareness, and minimum masking levels as well as loudness discomfort levels. Improvements increased with time over the first 6 months of therapy, at which time 91 % of all subjects across the 2 groups reported an improvement in tinnitus disturbance (as measured by the Tinnitus Reaction Questionnaire) of at least 40 %, with a mean improvement of 65 %. Furthermore, 80 % of subjects at 6 months reported a level of tinnitus disturbance that was no longer clinically significant. There was some indication of a more consistent benefit over 12 months for the group that was provided initially with a high level of tinnitus interaction; however, inter-group differences were not statistically significant. A relation between reported treatment usage (hours per day) and clinical outcomes was observed, suggesting that a "dosage effect" may apply with the stimulus provided. The authors concluded that this study found that the NNT provides rapid and profound improvements to the severity of tinnitus symptoms and their effect on the subject's quality of life. This was a consistent effect, provided by a treatment that subjects reported as being pleasant to use. Both of the stage-based variations of the treatment that were tested in this study were shown to be successful in achieving these outcomes.
Davis and associates (2008) conducted another clinical study on the effectiveness of NTT. This treatment approach is provided as part of a structured rehabilitation program. In this study, patients who received the customized stimulus (NTT group) reported significantly greater and more consistent alleviation of tinnitus symptoms than did patients who participated in a counseling and support program with and without delivery of a broad-band noise stimulus (Noise + Counseling group and Counseling-Only group, respectively). After 6 months of treatment, 86 % of the NTT patients met the minimum criterion for clinical success, defined as an alleviation of tinnitus disturbance of at least 40 % (as judged by the Tinnitus Reaction Questionnaire score). By contrast, only 47 % and 23 % of the Noise + Counseling and Counseling-Only groups, respectively, reported a successful result according to this criterion. Mean improvements in tinnitus disturbance scores in the NNT, Noise+Counseling, and Counseling-Only groups were 66 %, 22 %, and 15 %, respectively. The differences between the NTT group and the control groups were statistically significant. Significant differences were observed in other clinical outcomes. Patient reports of user acceptability were more consistently positive in the NTT group. It is unclear whether they wren overlapping of patients in these two studies.
The major drawbacks of these two studies were (i) small numbers of subjects, and (ii) short-term follow-up (not exceeding 12 months). Moreover, it is unclear whether they were overlapping of patients in these two studies. These findings need to be validated by further investigation.
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