Acta Oto-Laryngologica. 2014; 134: 159–167
ORIGINAL ARTICLE
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Effectiveness of transcutaneous electrical stimulation for chronic tinnitus
SUN KYU LEE, HOON CHUNG, JI HYUN CHUNG, SEUNG GUN YEO, MUN SUH PARK & JAE YONG BYUN Department of Otolaryngology – Head and Neck Surgery, College of Medicine, Kyung Hee University, Seoul, Korea
Abstract Conclusion: Based on the Tinnitus Handicap Inventory (THI) and visual analog scale (VAS) scores, transcutaneous electrical stimulation (TENS) can provide relief from tinnitus. Response to electrical stimulation was best seen in patients with lowfrequency tinnitus and with mild hearing loss. Objective: TENS is known to alleviate symptoms of tinnitus. However, study of the effectiveness of TENS for tinnitus has produced variable results, and it is still unclear what kind of patients with tinnitus would respond best to TENS. Here, we assessed the effects of TENS on the perception of tinnitus using the THI and VAS questionnaires. Methods: A total of 65 patients with tinnitus were divided into two groups: 45 patients received TENS and 20 patients received placebo (sham stimulation) twice a week over 4 weeks. THI and VAS scores were assessed before and after electrical stimulation. We also evaluated the effects of TENS on the degree of initial hearing loss and tinnitus frequency. Results: Twenty-eight of 45 patients (62.2%) revealed subjective improvement in tinnitus with TENS. TENS was more effective in patients with low-frequency tinnitus or with mild hearing loss. Symptomatic improvement in the electrical stimulation group was achieved for 1 month in most patients.
Keywords: Hearing loss, Tinnitus Handicap Inventory, THI
Introduction Tinnitus, characterized by the sensation of sound with no apparent source, accompanies a variety of diseases and involves all portions of the auditory pathway ranging from the external ear to the cerebral cortex [1]. Treatment of tinnitus remains challenging as the underlying causes are unknown. As the mechanism for tinnitus continues to undergo study, many treatments such as pharmacotherapy, biofeedback, acoustic masking, and psychotherapy have all been attempted. However, to date, there is no established treatment protocol [2]. Of the various treatments for tinnitus, electrical stimulation represents a unique form of sound therapy first used at least 120 years ago. Volta first attempted electrical stimulation of the inner ear [3], and House et al. reported tinnitus suppression as a beneficial side effect
of cochlear implantation in patients with profound hearing impairment [4]. Suppression of tinnitus by electrical stimulation of the preauricular skin, mastoid, eardrum, promontory, round window, and within the cochlea has been employed since the 1960s and 1970s [3,5,6]. Early results demonstrated that positive polarity was able to suppress tinnitus, and negative polarity produced the sensation of sound. It has been purported that this therapy leads to hyperpolarization of neural fibrils and thus inhibits or reduces the spontaneous firing rate by changing basal membrane potential, presumably due to increased microcirculation of the auditory pathways [7]. The efficacy of transcutaneous electrical stimulation (TENS) has been reported at up to 80%, although rates fluctuate depending on experimental design. Longterm improvements in tinnitus also vary from hours to weeks. TENS represents a noninvasive and simple
Correspondence: Jae Yong Byun MD, Department of Otolaryngology – Head and Neck Surgery, Kyung Hee University Hospital at Gangdong, Sangil-dong, Gangdong-gu, Seoul, Korea, 134-727. E-mail: [email protected]
(Received 1 July 2013; accepted 8 September 2013) ISSN 0001-6489 print/ISSN 1651-2251 online 2014 Informa Healthcare DOI: 10.3109/00016489.2013.844854
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method but has limitations given that underlying mechanisms remain uncertain and treatment efficacy is not consistent [8]. The aim of this study was to evaluate the efficacy of TENS on the external pinna in patients with chronic tinnitus and to investigate the features of tinnitus that may impact treatment. Material and methods
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Subjects Patients diagnosed with subjective, unilateral tinnitus and followed up for longer than 6 months in KyungHee University Hospital, Gangdong from February 2007 to March 2008 were included in this study. Each patient provided an otologic history and underwent physical examination. Subjects with chronic otitis media, neurological or hormonal disturbances, cerebrovascular disease, treatable forms of tinnitus, or receiving medications or other treatments for tinnitus were excluded. Due to the nature of the proposed treatment, we also excluded patients with any internal electrical device (for example, cardiac pacemakers and metal plates). All subjects had suffered from perceived tinnitus for a minimum of 6 months. Informed consent was obtained from each patient before initiating treatment. In total, 65 patients with chronic, subjective tinnitus were randomized to the treatment arm (electrical stimulation) or to the control arm (sham stimulation), allowing for a prospective, single-blind, randomized control (RCT) study to be conducted. The electrical stimulation group consisted of 45 patients subjected to TENS twice a week for 4 weeks. The sham stimulation group consisted of 20 patients who underwent electrical stimulus attachment but did not receive any stimulus during the same time-frame. During the
A
electrical stimulation period, no other treatments for tinnitus including medications or psychotherapy were administered. Otologic and audiologic evaluations Patients underwent an otologic history and audiologic evaluation. Tests included audiometry for pure-tone average (PTA), speech reception threshold, and impedance battery. Brainstem audiometry was performed in all patients to exclude retrocochlear lesions. Analysis of tinnitus was accomplished using stimulated sounds from a Norwest SG-1 Tinnitus Synthesizer (GN otometrics, copenhagen, Denmark), with the experimenter adjusting the synthesized frequency and intensity level according to the manufacturer’s instructions. To evaluate the effects of percutaneous electrical stimulation according to hearing levels, patients were divided into five groups (normal, mild, moderate, moderate-severe, and severe) based on average pure-tone threshold (average of responses at 500, 1000, and 2000 Hz) and according to ANSI classification (1969). In addition, to investigate the relationship between tinnitus features and treatment efficacy, patients were divided into a low-frequency tinnitus group (0.25– 2 kHz) and a high-frequency tinnitus group (4–8 kHz) based on the tinnitogram. Electrical stimulation After auricles were cleaned with alcohol, probes were placed at 5 of 13 possible points where electrical resistance was low and conductance of the electrical current was high relative to the surrounding area (Figure 1) [9].
B
Figure 1. (A) Physiotense device (Physiomed Inc., Germany). (B) Illustration of sites used for transcutaneous electrical stimulation (TENS). In total, 13 points were located by characteristics of low electrical resistance with resulting high electrical current conductance relative to the surrounding area. The stimulus was applied to five sites that we chose on the auricle of the ear with tinnitus.
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TENS for tinnitus Stimulation was performed using the Physiotense (Physiomed Inc., Schnaittach/Laipersdorf, Germany), which generates alternating currents with a frequency of 50 Hz (Figure 1). Current intensity was 15 mA. The device has on/off, pulse-square, frequency, and current intensity buttons. An alternating, pulsed current at low frequency (50 Hz) was used for tinnitus suppression. Hand-held electrodes were placed on the external pinna and stimulation duration was 30 s for each point. In total, therapy sessions for each patient were instituted twice a week for a total of eight therapy sessions over 4 weeks. For the sham stimulation group, the treatment paradigm was identical to the electrical stimulation group except that the power supply was turned off and current was not delivered from the probe. Of note, even in the electrical stimulation group, patients are not able to feel sound vibrations or sense current delivery. Patients were unaware of the treatment group to which they were assigned. Assessment of the severity of tinnitus Patients completed questionnaires including the visual analog scale (VAS) and the Korean adaptation of the Tinnitus Handicap Inventory (THI) [10] both before electrical stimulation and after treatment. Tinnitus severity was assessed via VAS scores for four subgroups: duration, loudness, annoyance, and difficulty in activities of daily life. Patients were asked to rate each item within the subgroup on a scale of 0 to 10 points, with 0 indicating no symptoms and 10 denoting greatest discomfort. THI represents a validated and widely used questionnaire for assessing the impact of tinnitus in daily life. It consists of a 25-item survey that provides a total score and 3 subscale scores (functional, emotional, and catastrophic subscale scores). Each of the 25 items has 3 potential answers with ‘yes’ assigned four points, ‘sometimes’ two points, and ‘no’ zero points. Total scores range from 0 to 100, with 0 being asymptomatic and 100 representing the worst possible symptoms. When pretreatment and post-treatment total THI scores differed by more than 10 points, we defined such interventions as helpful. When pretreatment and post-treatment total THI scores differed by less than 10 points, such interventions were defined as not helpful.
calculation of the sample size. The mean and standard deviation of each arm from key references were used, and we planned this study as an unequal RCT (the ratio of sample Arm2:Arm1 was 2:1) to avoid ethical problems and save time. Statistical analysis was performed with the Statistical Package for Social Science 18.0 (SPSS Inc., Chicago, IL, USA). Because VAS and THI scores are nonparametric values, Wilcoxon signed rank test was performed to analyze the difference between pretreatment and post-treatment. The effect of electrical stimulation, frequency of tinnitus, and coexisting hearing loss was analyzed by multi-way analysis of variance (ANOVA). For all analyses, p values < 0.05 were considered statistically significant. Results In total, 65 patients with chronic tinnitus (39 males and 26 females; average age 46.2 ± 13.9 years) participated in the study. The duration of tinnitus ranged from 3 months to 8 years (median duration 24.44 ± 19.79 months). Demographic and clinical characteristics of both the electrical stimulation and sham stimulation groups are shown in Table I. Based on pretreatment and post-treatment changes in THI scores, 28 patients (62.2%) from the electrical stimulation group received helpful benefits, whereas only two patients (10%) from the sham stimulation group were satisfied (Table II). Comparison of VAS scores and THI scores in electrical stimulation and sham stimulation groups In the electrical stimulation group, VAS scores demonstrated statistically significant improvements in all subscales. VAS scores for duration declined from 6.9 (pretreatment) to 5.6 (post-treatment). VAS scores for loudness were 6.7 (pretreatment) and 5.8 (post-treatment), and for annoyance were reduced from 6.7 (pretreatment) to 5.4 (post-
Table I. Clinical characteristics of the study patients. Electrical stimulation group
Sham stimulation group
Sex (M:F)
26:19
13:7
Age (years)
46.6 ± 13.9
45.6 ± 11.5
20:25
8:12
38.1 ± 6.4
36.4 ± 5.2
Characteristic
Statistical analysis When we designed this study, we obtained an appropriate sample size by using the SAS 9.3 program. We applied an alpha value of 0.05, power of 0.80, and a two-sided condition as an analytic parameter for
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Side of tinnitus (right:left) Hearing level of the side with tinnitus (dB)
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Table II. Performance rating of electrical stimulation for tinnitus according to the Tinnitus Handicap Inventory (THI) score. Group
Helpful, n (%)
Not helpful, n (%)
Transcutaneous electrical stimulation (n = 45)
28 (62.2)
17 (37.8)
Sham stimulation (n = 20)
2 (10.0)
18 (90.0)
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Helpful: THI benefit (pretreatment – post-treatment) score is more than 10 points. Not helpful: THI benefit (pretreatment – posttreatment) score is less than 10 points.
treatment). Pretreatment and post-treatment VAS scores for difficulty in activities of daily life were 6.8 and 5.4, respectively. In the sham stimulation group, pretreatment VAS scores for duration, loudness, annoyance, and difficulty in activities of daily life were 6.5, 6.2, 6.5, and 6.6, respectively. Following sham electrical stimulation, VAS scores decreased to 6.1, 5.6, 5.7, and 6.5, respectively. There were no significant differences between pretreatment and post-treatment VAS scores (Table III). Baseline mean THI scores were 49.4 for the electrical stimulation group and 44.5 for the sham stimulation group. Man–Whitney U test determined that baseline means were not significantly different (p > 0.05). Following treatment, the mean THI score significantly decreased to 42.8 in the electrical
stimulation group. In the sham stimulation group, the mean THI score increased to 45.2, but no significant difference was identified. After electrical stimulation, emotional and catastrophic subscales of THI significantly improved. In the sham stimulation group, functional subscale scores significantly increased and there was no significant change of score for other subscales (Table III).
Relationship between frequency of tinnitus, degree of hearing disturbance, and treatment effect of electrical stimulation In the electrical stimulation group, patients were divided into two subgroups based on the distribution of tinnitus frequency, with 25 patients having lowfrequency tinnitus (0.25–2 kHz) and 20 patients having high-frequency tinnitus (4–8 kHz). To analyze the relationship between tinnitus frequency and electrical stimulation efficacy, changes in THI and VAS scores were assessed. In the electrical stimulation group with lowfrequency tinnitus, the pretreatment VAS score for duration was 7.4 and the post-treatment score was 3.8. VAS scores for loudness reduced from 6.7 to 5.1 following treatment, and VAS scores for annoyance reduced from 6.5 to 5.0 with treatment. VAS scores for difficulty in activities of daily living decreased from
Table III. Comparison of changes in visual analog scale (VAS) score and tinnitus handicap inventory (THI) score between electrical stimulation and sham stimulation. Assessment VAS
Subscale Duration
Loudness
THI
Group
Prestimulation
Post-stimulation
p value
TENS
6.9 ± 1.6
5.6 ± 2.1
< 0.05*
Sham
6.5 ± 1.2
6.1 ± 1.5
> 0.05
TENS
6.7 ± 1.7
5.8 ± 1.9
< 0.05*
Sham
6.2 ± 1.9
5.6 ± 1.6
> 0.05
Annoyance
TENS
6.7 ± 1.5
5.4 ± 2.2
< 0.05*
Sham
6.5 ± 1.7
5.7 ± 2.2
> 0.05
Difficulty in activities of daily life
TENS
6.8 ± 1.9
5.4 ± 1.9
< 0.05*
Sham
6.6 ± 1.7
6.5 ± 1.3
> 0.05
Functional
TENS
46.3 ± 20.7
45.4 ± 15.9
> 0.05
Sham
43.8 ± 13.1
49.5 ± 11.7
< 0.05*
TENS
50.2 ± 21.5
31.9 ± 17.3
< 0.05*
Emotional
Sham
42.1 ± 15.6
40.5 ± 15.5
> 0.05
Catastrophic
TENS
51.6 ± 21.7
37.4 ± 16.1
< 0.05*
Sham
47.7 ± 13.9
46.2 ± 13.3
> 0.05
Total
TENS
49.4 ± 9.9
42.8 ± 8.7
< 0.05*
Sham
44.5 ± 6.5
45.2 ± 7.9
> 0.05
Results are given as mean ± standard deviation. TENS, transcutaneous electrical stimulation. *p < 0.05.
TENS for tinnitus
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Table IV. Treatment results according to tinnitus frequency. Low-frequency tinnitus Assessment
Subscale
Visual analog scale Duration
Loudness
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Annoyance
High-frequency tinnitus
Group Prestimulation Post-stimulation p value
Prestimulation Post-stimulation p value
TENS
7.4 ± 1.7
3.8 ± 1.5
< 0.05*
6.5 ±1.2
6.0 ± 1.3
> 0.05
Sham
5.7 ± 1.2
5.4 ± 1.7
> 0.05
7.0 ± 1.0
6.5 ± 1.3
> 0.05
TENS
6.7 ± 1.5
5.1 ± 1.9
< 0.05*
7.2 ± 1.4
7.0 ± 1.1
> 0.05
Sham
6.3 ± 2.2
5.4 ± 1.7
> 0.05
7.1 ± 1.8
6.7 ± 1.7
> 0.05
TENS
6.5 ± 1.5
5.0 ± 2.2
< 0.05*
7.1 ± 1.7
5.8 ± 1.5
< 0.05*
Sham
6.4 ± 2.1
6.5 ± 1.2
> 0.05
6.5 ± 1.6
6.2 ± 2.5
> 0.05
6.6 ± 1.9
5.3 ± 1.9
< 0.05*
7.1 ± 1.1
5.7 ± 1.7
< 0.05*
Difficulty in activities TENS of daily life Sham
7.2 ± 2.0
7.0 ± 1.1
> 0.05
7.2 ± 1.5
6.2 ± 1.4
> 0.05
Tinnitus Handicap Functional Inventory
TENS
49.4 ± 20.7
47.0 ± 17.4
< 0.05*
47.9 ± 13.0
45.0 ± 12.1
> 0.05
Sham
42.0 ± 17.0
43.8 ± 13.8
> 0.05
44.8 ± 11.1
51.8 ± 9.9
< 0.05*
Emotional
TENS
54.4 ± 21.7
28.7 ± 15.2
< 0.05*
45.9 ± 14.7
32.2 ± 12.3
< 0.05*
Sham
51.5 ± 17.6
48.4 ± 15.5
> 0.05
42.4 ± 15.2
41.6 ± 16.1
> 0.05
Catastrophic
TENS
53.5 ± 20.5
38.0 ± 17.3
< 0.05*
49.5 ± 17.5
35.5 ± 13.2
< 0.05*
Sham
53.7 ± 16.7
48.7 ± 16.7
> 0.05
49.8 ± 12.4
44.8 ± 11.6
> 0.05
Total
TENS
51.8 ± 10.1
39.9 ± 9.1
< 0.05*
47.7 ± 11.4
37.1 ± 9.8
> 0.05
Sham
52.4 ± 16.7
53.6 ± 10.4
> 0.05
45.7 ± 5.8
46.1 ± 6.5
> 0.05
Results are given as mean ± standard deviation. TENS, transcutaneous electrical stimulation. *p < 0.05.
6.6 to 5.3 after treatment. All changes in VAS scores were statistically significant (p < 0.05). For THI scores, whole subscales showed significant improvement after treatment and total THI scores also decreased significantly after treatment (Table IV). In the electrical stimulation group with highfrequency tinnitus, VAS scores for all subscales improved following electrical stimulation, but only two items – annoyance and difficulty in activities of daily life – exhibited statistically significant decreases. Mean total THI score changed from 47.7 to 37.1 with treatment. Functional subscale score decreased from 47.9 to 45.0, emotional stress score changed from 45.9 to 32.2, and catastrophic subscale score decreased from 49.5 to 35.5. All THI scores decreased, but only improvements in emotional stress and catastrophic subscales were statistically significant (Table IV). To analyze the association between degree of hearing disturbance and effect of electrical stimulation, patients in the electrical stimulation group were divided into five subgroups of hearing disturbance: normal, mild, moderate, moderately severe, and severe, according to ISO classification. VAS and THI scores before and after electrical stimulation were calculated. Clinical improvement following treatment for all five hearing level subgroups was compared. In the normal-hearing level group, all VAS subscales and THI scores showed significant improvements. The mild hearing disturbance
group also showed statistically significant improvements inallsubscalesexceptVASscorefordifficultyinactivities of daily life. However, in the severe hearing disturbance group, only the VAS score for difficulty in activities of daily life decreased significantly (Figures 2 and 3). The degree of hearing disturbance and frequency of tinnitus were analyzed simultaneously with multi-way ANOVA, and the statistical value of the difference in the VAS and THI scores according to treatment was compared. The actual therapeutic effect of electrical stimulation on the frequency of tinnitus and degree of hearing disturbance was analyzed with multi-way ANOVA. The interactions among the three variables (treatment arm, frequency of tinnitus, and degree of hearing disturbance) with the changes in the VAS and THI scores were not significant (treatment arm – frequency of tinnitus: p = 0.770, p = 0.070; treatment arm – degree of hearing disturbance: p = 0.395, p = 0.822; frequency of tinnitus – degree of hearing disturbance: p = 0.542, p = 0.860). With multi-way ANOVA, changes in the VAS and THI scores were significantly different between electrical stimulation and sham stimulation (p = 0.046, p = 0.017), and changes in the THI scores between patients with lowand high-frequency tinnitus were significantly different (p = 0.048). Moreover, the change in the THI score was significant according to the degree of hearing disturbance (p = 0.048) (Table V).
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*
8
6
Pre Post
4 2
6
ML Mod MS Change of awareness
4
Se
NL
10
ML Mod MS Change of loudness
Se
10 * *
*
6
Pre Post
4
*
8
*
2
VAS score
VAS score
Pre Post
0 NL
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*
*
2
0
8
*
*
VAS score
VAS score
8
6
Pre Post
4 2
0
0 NL
ML Mod MS Change of annoyance
Se
NL
ML Mod MS Change of effect on life
Se
Figure 2. Change in visual analog scale (VAS) score according to degree of hearing disturbance following electrical stimulation. ML, mild; Mod, moderate; MS, moderate-severe; NL, normal; Pre, pretreatment; Post, after treatment; Se, severe. *p < 0.05.
Considering the results of the study, actual TENS, low-frequency tinnitus, and normal hearing/mild hearing disturbance were associated with significant changes in the THI score.
Improvement in duration of tinnitus after electrical stimulation Duration of tinnitus suppression varied from a few hours to several months. To summarize, 14 patients (31%) received symptomatic relief for less than 1 week and 16 patients (36%) had benefits lasting less than 1 month. Only two patients (4%) had effects lasting longer than 3 months – of note, these two patients had low-frequency tinnitus and mild hearing loss.
Side effects of TENS Mild side effects were seen in eight patients including four patients with dizziness, three patients with headache, and one patient with facial numbness. However, side effects dissipated after cessation of treatment.
Discussion The use of electrical currents to alter physiologic responses has been recognized since the 1800s, and electrical stimulation has been used to treat inflammation, pain, edema, joint dysfunction, and spinal disorders [11,12]. Electrical stimulation for the treatment of tinnitus remains an intriguing therapeutic option. Interestingly, reduction in tinnitus symptoms has been reported as a beneficial side effect following cochlear implantation [4]. In 1977, Graham and Hazell [5] demonstrated tinnitus suppression in two of nine patients via transtympanic stimulation of the promontory with alternating currents. In 1979, Portmann et al. [13] reported an 87% success rate of temporary suppression of tinnitus by electrical stimulation. TENS for tinnitus was reported by Chouard et al. [14] in 1981, with greater than onethird of patients experiencing significant reduction in tinnitus symptoms. Engelberg and Bauer [9] in 1985 reported an 82% improvement in tinnitus symptoms with TENS in a sample of 20 patients. Recent evidence demonstrated a success rate of roughly 50% in 500 patients with tinnitus of varying etiology using electrical stimulation [8]. However, given the
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TENS for tinnitus 100
100
80
80
60
*
* Pre Post
40
THI score
THI score
*
20
ML Mod MS Functional subscale
*
60
Pre Post
40
Se
NL
100
ML Mod MS Se Emotional subscale
100
80
80 *
*
Pre Post
40 20
THI score
* THI score
*
0 NL
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*
20
0
60
*
* 60
* Pre Post
* 40 20
0
0 NL
ML Mod MS Se Catastrophic subscale
NL
ML
Mod Total THI
MS
Se
Figure 3. Change in Tinnitus Handicap Inventory (THI) score according to degree of hearing disturbance following electrical stimulation. ML, mild; Mod, moderate; MS, moderate-severe; NL, normal; Pre, pretreatment; Post, after treatment; Se, severe. *p < 0.05.
subjective nature of tinnitus, evaluation of treatment efficacy remains difficult. In this study, we evaluated the efficacy of TENS in the management of tinnitus through the use of VAS and THI questionnaires – validated and widely used methods for assessing the impact of tinnitus on daily life. Not surprisingly, conflicting results of electrical therapy for tinnitus have been reported, as many Table V. Statistical value of change in visual analog scale (VAS) score and Tinnitus Handicap Inventory (THI) score analyzed by multi-way ANOVA. p value Change in VAS score
Change in THI score
TENS vs sham procedure
0.046*
0.017*
Low-frequency tinnitus vs high-frequency tinnitus
0.219
0.048*
Degree of hearing disturbance
0.492
0.049*
Factor
*p < 0.05.
factors can influence treatment efficacy including currency of the electrical stimulation and location of stimulation [15]. Currency of the electrical stimulation may be important; however, no clear superiority between direct and alternating currents on tinnitus suppression has emerged. While direct current seems more effective in cochlear stimulation, this method of electrical stimulation should only be employed in patients with severe hearing loss due to the possibility of cochlear damage. Hazell et al. [16] demonstrated that electrical suppression of tinnitus is frequency dependent, with low-frequency stimuli being more effective. The authors concluded that frequency characteristics of tinnitus suppression and auditory discomfort are divergent phenomena at low frequencies, and frequencies higher than 100 Hz should be avoided. The application site of electrical stimulation remains a topic for continued study. Some evidence indicates that electrical stimulation should be administered close to cochlear neurons. Kuk et al. [17]
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reported a reduction in tinnitus in 50% of patients using alternating current via the eardrum. Vernon and Fenwick [18] used preauricular and postauricular electrical suppression of tinnitus in 50 patients and found decreases in tinnitus intensity in 28% of patients as compared with only 2% of patients receiving placebo stimulation. Similarly, in a large caseseries, Steenerson and Cronin [8] used preauricular stimulation and reported a 53% success rate in tinnitus reduction. Based on the aforementioned results, we used a stimulator that generates an alternating current with a frequency of 50 Hz, a level that has previously been reported as most effective for tinnitus suppression. Current intensity was 15 mA, and there were no complications. The placebo effect is often difficult to assess; however, in the present study, electrical stimulation was inaudible and produced no sensation, allowing for blind testing. In addition, we analyzed several variables between the electrical stimulation group and the sham stimulation group. There were no significant differences between the two groups; therefore, we believe that sham stimulation played a role as a true control. As expected, the number of patients who benefited from therapy was higher in the electrical stimulation group than in the sham testing group. We also evaluated the relationships among treatment efficacy, hearing level, and tinnitus frequency. Here, patients with low-frequency tinnitus were more susceptible to electrical stimulation. It has been demonstrated previously that outer hair cell motility increases in response to electrical stimulation. Electrically stimulated outer hair cells can provide inputs to the basilar membrane that, in turn, can excite inner hair cells and elicit synaptically mediated long-latency responses of the auditory nerve and main superior olivary nuclei [19]. According to the tonotopicity of the superior olivary complex, hair cells that respond to low frequency are located ventrolaterally, and hair cells that respond to high frequency are found dorsomedially [20]. Following transcutaneous stimulation, hair cells located more laterally could react faster than at other sites. Therefore, patients with lowfrequency tinnitus may experience better therapeutic effects. Our results suggest that TENS can be effective for tinnitus of various hearing levels as the degree of tinnitus suppression was not significantly different between hearing levels. The site of and mechanism by which electrical stimulation produces tinnitus relief remain unclear. Further research is necessary to determine optimal conditions for electrical stimulation in treating tinnitus.
Conclusions Approximately 62% of patients suffering from tinnitus experience considerable symptomatic relief following TENS. While tinnitus does not completely dissipate, distressing features of tinnitus often disappear with electrical stimulation. Electrical stimulation appears more effective in patients with low-frequency tinnitus or mild hearing loss. Electrotherapy can be repeated without notable risks. Large-scale application of this treatment modality may be helpful to better characterize the underlying mechanisms of tinnitus. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
References [1] Kaada B, Hognestad S, Havstad J. Transcutaneous nerve stimulation (TNS) in tinnitus. Scand Audiol 1989;18:211– 17. [2] Goodey R. Tinnitus treatment: state of the art. Prog Brain Res 2007;166:237–46. [3] Cazals Y, Negrevergne M, Aran JM. Electrical stimulation of the cochlea in man: hearing induction and tinnitus suppression. J Am Audiol Soc 1978;3:209–13. [4] House WF, Berliner KI, Crary WG. Cochlear implants. Ann Otol Rhinol Laryngol 1976;85:1–93. [5] Graham JM, Hazell JWP. Electrical stimulation of the human cochlea using a transtympanic electrode. Br J Audiol 1977; 11:59–62. [6] Aran JM, Wu ZY, Charle de Sauvage R, Cazals Y, Portmann M. Electrical stimulation of the ear: experimental studies. Ann Otol Rhinol Laryngol 1983;92:614–20. [7] Konopka W, Zalewski P, Olszewski J, Olszewska-Ziaber A, Pietkiewicz P. Tinnitus suppression by electrical promontory stimulation in patients with sensorineural hearing loss. Auris Nasus Larynx 2001;28:35–40. [8] Steenerson RL, Cronin GW. Treatment of tinnitus with electrical stimulation. Otolaryngol Head Neck Surg 1999; 121:511–13. [9] Engelberg M, Bauer W. Transcutaneous electrical stimulation for tinnitus. Laryngoscope 1985;95:1167–73. [10] Kim JH, Lee SY, Kim CH, Lim SL, Shin JN, Chung WH, et al. Reliability and validity of a Korean adaptation of the Tinnitus Handicap Inventory. Korean J Otolaryngol-Head Neck Surg 2002;45:328–34. [11] Gault WR, Gatens PF. Use of low intensity direct current in management of ischemic skin ulcers. Phys Ther 1976;56: 265–7. [12] Bowman BR, Baker LL, Waters RL. Positional feedback and electrical stimulation: an automated treatment for the hemiplegic wrist. Arch Phys Med Rehab 1979;60:497–9. [13] Portmann M, Cazals Y, Negrevergne M, Aran JM. Temporary tinnitus suppression in man through electrical stimulation of the cochlea. Acta Otolaryngol 1979;87:294–9. [14] Chouard CH, Meyer B, Maridat D. Transcutaneous electrotherapy for severe tinnitus. Acta Otolaryngol 1981;91: 415–22.
TENS for tinnitus
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[15] Rubinstein JT, Tyler RS. 2004. Electrical suppression of tinnitus. In Snow JB Jr, editor. Tinnitus: theory and management. Lewiston, NY: BC Decker. p 326–35. [16] Hazell JW, Jastreboff PJ, Meerton LE, Conway MJ. Electrical tinnitus suppression: frequency dependence of effects. Audiology 1993;32:68–77. [17] Kuk FK, Tyler RS, Rustand N, Harker LA, Tye-Murray N. Alternating current at the eardrum for tinnitus reduction. J Speech Hear Res 1989;32:393–400.
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[18] Vernon JA, Fenwick JA. Attempts to suppress tinnitus with transcutaneous electrical stimulation. Otolaryngol Head Neck Surg 1985;93:385–9. [19] Cevette MJ, Cocco D, Pradhan GN, Galea AM, Wagner LS, Oakley SR, et al. The effect of galvanic vestibular stimulation on distortion product otoacoustic emissions. J Vestib Res 2012;22:17–25. [20] Cooper NP, Rhode WS. Basilar membrane tonotopicity in the hook region of the cat cochlea. Hear Res 1992;63:191–6.
ORIGINAL ARTICLE
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Effectiveness of transcutaneous electrical stimulation for chronic tinnitus
SUN KYU LEE, HOON CHUNG, JI HYUN CHUNG, SEUNG GUN YEO, MUN SUH PARK & JAE YONG BYUN Department of Otolaryngology – Head and Neck Surgery, College of Medicine, Kyung Hee University, Seoul, Korea
Abstract Conclusion: Based on the Tinnitus Handicap Inventory (THI) and visual analog scale (VAS) scores, transcutaneous electrical stimulation (TENS) can provide relief from tinnitus. Response to electrical stimulation was best seen in patients with lowfrequency tinnitus and with mild hearing loss. Objective: TENS is known to alleviate symptoms of tinnitus. However, study of the effectiveness of TENS for tinnitus has produced variable results, and it is still unclear what kind of patients with tinnitus would respond best to TENS. Here, we assessed the effects of TENS on the perception of tinnitus using the THI and VAS questionnaires. Methods: A total of 65 patients with tinnitus were divided into two groups: 45 patients received TENS and 20 patients received placebo (sham stimulation) twice a week over 4 weeks. THI and VAS scores were assessed before and after electrical stimulation. We also evaluated the effects of TENS on the degree of initial hearing loss and tinnitus frequency. Results: Twenty-eight of 45 patients (62.2%) revealed subjective improvement in tinnitus with TENS. TENS was more effective in patients with low-frequency tinnitus or with mild hearing loss. Symptomatic improvement in the electrical stimulation group was achieved for 1 month in most patients.
Keywords: Hearing loss, Tinnitus Handicap Inventory, THI
Introduction Tinnitus, characterized by the sensation of sound with no apparent source, accompanies a variety of diseases and involves all portions of the auditory pathway ranging from the external ear to the cerebral cortex [1]. Treatment of tinnitus remains challenging as the underlying causes are unknown. As the mechanism for tinnitus continues to undergo study, many treatments such as pharmacotherapy, biofeedback, acoustic masking, and psychotherapy have all been attempted. However, to date, there is no established treatment protocol [2]. Of the various treatments for tinnitus, electrical stimulation represents a unique form of sound therapy first used at least 120 years ago. Volta first attempted electrical stimulation of the inner ear [3], and House et al. reported tinnitus suppression as a beneficial side effect
of cochlear implantation in patients with profound hearing impairment [4]. Suppression of tinnitus by electrical stimulation of the preauricular skin, mastoid, eardrum, promontory, round window, and within the cochlea has been employed since the 1960s and 1970s [3,5,6]. Early results demonstrated that positive polarity was able to suppress tinnitus, and negative polarity produced the sensation of sound. It has been purported that this therapy leads to hyperpolarization of neural fibrils and thus inhibits or reduces the spontaneous firing rate by changing basal membrane potential, presumably due to increased microcirculation of the auditory pathways [7]. The efficacy of transcutaneous electrical stimulation (TENS) has been reported at up to 80%, although rates fluctuate depending on experimental design. Longterm improvements in tinnitus also vary from hours to weeks. TENS represents a noninvasive and simple
Correspondence: Jae Yong Byun MD, Department of Otolaryngology – Head and Neck Surgery, Kyung Hee University Hospital at Gangdong, Sangil-dong, Gangdong-gu, Seoul, Korea, 134-727. E-mail: [email protected]
(Received 1 July 2013; accepted 8 September 2013) ISSN 0001-6489 print/ISSN 1651-2251 online 2014 Informa Healthcare DOI: 10.3109/00016489.2013.844854
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method but has limitations given that underlying mechanisms remain uncertain and treatment efficacy is not consistent [8]. The aim of this study was to evaluate the efficacy of TENS on the external pinna in patients with chronic tinnitus and to investigate the features of tinnitus that may impact treatment. Material and methods
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Subjects Patients diagnosed with subjective, unilateral tinnitus and followed up for longer than 6 months in KyungHee University Hospital, Gangdong from February 2007 to March 2008 were included in this study. Each patient provided an otologic history and underwent physical examination. Subjects with chronic otitis media, neurological or hormonal disturbances, cerebrovascular disease, treatable forms of tinnitus, or receiving medications or other treatments for tinnitus were excluded. Due to the nature of the proposed treatment, we also excluded patients with any internal electrical device (for example, cardiac pacemakers and metal plates). All subjects had suffered from perceived tinnitus for a minimum of 6 months. Informed consent was obtained from each patient before initiating treatment. In total, 65 patients with chronic, subjective tinnitus were randomized to the treatment arm (electrical stimulation) or to the control arm (sham stimulation), allowing for a prospective, single-blind, randomized control (RCT) study to be conducted. The electrical stimulation group consisted of 45 patients subjected to TENS twice a week for 4 weeks. The sham stimulation group consisted of 20 patients who underwent electrical stimulus attachment but did not receive any stimulus during the same time-frame. During the
A
electrical stimulation period, no other treatments for tinnitus including medications or psychotherapy were administered. Otologic and audiologic evaluations Patients underwent an otologic history and audiologic evaluation. Tests included audiometry for pure-tone average (PTA), speech reception threshold, and impedance battery. Brainstem audiometry was performed in all patients to exclude retrocochlear lesions. Analysis of tinnitus was accomplished using stimulated sounds from a Norwest SG-1 Tinnitus Synthesizer (GN otometrics, copenhagen, Denmark), with the experimenter adjusting the synthesized frequency and intensity level according to the manufacturer’s instructions. To evaluate the effects of percutaneous electrical stimulation according to hearing levels, patients were divided into five groups (normal, mild, moderate, moderate-severe, and severe) based on average pure-tone threshold (average of responses at 500, 1000, and 2000 Hz) and according to ANSI classification (1969). In addition, to investigate the relationship between tinnitus features and treatment efficacy, patients were divided into a low-frequency tinnitus group (0.25– 2 kHz) and a high-frequency tinnitus group (4–8 kHz) based on the tinnitogram. Electrical stimulation After auricles were cleaned with alcohol, probes were placed at 5 of 13 possible points where electrical resistance was low and conductance of the electrical current was high relative to the surrounding area (Figure 1) [9].
B
Figure 1. (A) Physiotense device (Physiomed Inc., Germany). (B) Illustration of sites used for transcutaneous electrical stimulation (TENS). In total, 13 points were located by characteristics of low electrical resistance with resulting high electrical current conductance relative to the surrounding area. The stimulus was applied to five sites that we chose on the auricle of the ear with tinnitus.
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TENS for tinnitus Stimulation was performed using the Physiotense (Physiomed Inc., Schnaittach/Laipersdorf, Germany), which generates alternating currents with a frequency of 50 Hz (Figure 1). Current intensity was 15 mA. The device has on/off, pulse-square, frequency, and current intensity buttons. An alternating, pulsed current at low frequency (50 Hz) was used for tinnitus suppression. Hand-held electrodes were placed on the external pinna and stimulation duration was 30 s for each point. In total, therapy sessions for each patient were instituted twice a week for a total of eight therapy sessions over 4 weeks. For the sham stimulation group, the treatment paradigm was identical to the electrical stimulation group except that the power supply was turned off and current was not delivered from the probe. Of note, even in the electrical stimulation group, patients are not able to feel sound vibrations or sense current delivery. Patients were unaware of the treatment group to which they were assigned. Assessment of the severity of tinnitus Patients completed questionnaires including the visual analog scale (VAS) and the Korean adaptation of the Tinnitus Handicap Inventory (THI) [10] both before electrical stimulation and after treatment. Tinnitus severity was assessed via VAS scores for four subgroups: duration, loudness, annoyance, and difficulty in activities of daily life. Patients were asked to rate each item within the subgroup on a scale of 0 to 10 points, with 0 indicating no symptoms and 10 denoting greatest discomfort. THI represents a validated and widely used questionnaire for assessing the impact of tinnitus in daily life. It consists of a 25-item survey that provides a total score and 3 subscale scores (functional, emotional, and catastrophic subscale scores). Each of the 25 items has 3 potential answers with ‘yes’ assigned four points, ‘sometimes’ two points, and ‘no’ zero points. Total scores range from 0 to 100, with 0 being asymptomatic and 100 representing the worst possible symptoms. When pretreatment and post-treatment total THI scores differed by more than 10 points, we defined such interventions as helpful. When pretreatment and post-treatment total THI scores differed by less than 10 points, such interventions were defined as not helpful.
calculation of the sample size. The mean and standard deviation of each arm from key references were used, and we planned this study as an unequal RCT (the ratio of sample Arm2:Arm1 was 2:1) to avoid ethical problems and save time. Statistical analysis was performed with the Statistical Package for Social Science 18.0 (SPSS Inc., Chicago, IL, USA). Because VAS and THI scores are nonparametric values, Wilcoxon signed rank test was performed to analyze the difference between pretreatment and post-treatment. The effect of electrical stimulation, frequency of tinnitus, and coexisting hearing loss was analyzed by multi-way analysis of variance (ANOVA). For all analyses, p values < 0.05 were considered statistically significant. Results In total, 65 patients with chronic tinnitus (39 males and 26 females; average age 46.2 ± 13.9 years) participated in the study. The duration of tinnitus ranged from 3 months to 8 years (median duration 24.44 ± 19.79 months). Demographic and clinical characteristics of both the electrical stimulation and sham stimulation groups are shown in Table I. Based on pretreatment and post-treatment changes in THI scores, 28 patients (62.2%) from the electrical stimulation group received helpful benefits, whereas only two patients (10%) from the sham stimulation group were satisfied (Table II). Comparison of VAS scores and THI scores in electrical stimulation and sham stimulation groups In the electrical stimulation group, VAS scores demonstrated statistically significant improvements in all subscales. VAS scores for duration declined from 6.9 (pretreatment) to 5.6 (post-treatment). VAS scores for loudness were 6.7 (pretreatment) and 5.8 (post-treatment), and for annoyance were reduced from 6.7 (pretreatment) to 5.4 (post-
Table I. Clinical characteristics of the study patients. Electrical stimulation group
Sham stimulation group
Sex (M:F)
26:19
13:7
Age (years)
46.6 ± 13.9
45.6 ± 11.5
20:25
8:12
38.1 ± 6.4
36.4 ± 5.2
Characteristic
Statistical analysis When we designed this study, we obtained an appropriate sample size by using the SAS 9.3 program. We applied an alpha value of 0.05, power of 0.80, and a two-sided condition as an analytic parameter for
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Side of tinnitus (right:left) Hearing level of the side with tinnitus (dB)
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Table II. Performance rating of electrical stimulation for tinnitus according to the Tinnitus Handicap Inventory (THI) score. Group
Helpful, n (%)
Not helpful, n (%)
Transcutaneous electrical stimulation (n = 45)
28 (62.2)
17 (37.8)
Sham stimulation (n = 20)
2 (10.0)
18 (90.0)
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Helpful: THI benefit (pretreatment – post-treatment) score is more than 10 points. Not helpful: THI benefit (pretreatment – posttreatment) score is less than 10 points.
treatment). Pretreatment and post-treatment VAS scores for difficulty in activities of daily life were 6.8 and 5.4, respectively. In the sham stimulation group, pretreatment VAS scores for duration, loudness, annoyance, and difficulty in activities of daily life were 6.5, 6.2, 6.5, and 6.6, respectively. Following sham electrical stimulation, VAS scores decreased to 6.1, 5.6, 5.7, and 6.5, respectively. There were no significant differences between pretreatment and post-treatment VAS scores (Table III). Baseline mean THI scores were 49.4 for the electrical stimulation group and 44.5 for the sham stimulation group. Man–Whitney U test determined that baseline means were not significantly different (p > 0.05). Following treatment, the mean THI score significantly decreased to 42.8 in the electrical
stimulation group. In the sham stimulation group, the mean THI score increased to 45.2, but no significant difference was identified. After electrical stimulation, emotional and catastrophic subscales of THI significantly improved. In the sham stimulation group, functional subscale scores significantly increased and there was no significant change of score for other subscales (Table III).
Relationship between frequency of tinnitus, degree of hearing disturbance, and treatment effect of electrical stimulation In the electrical stimulation group, patients were divided into two subgroups based on the distribution of tinnitus frequency, with 25 patients having lowfrequency tinnitus (0.25–2 kHz) and 20 patients having high-frequency tinnitus (4–8 kHz). To analyze the relationship between tinnitus frequency and electrical stimulation efficacy, changes in THI and VAS scores were assessed. In the electrical stimulation group with lowfrequency tinnitus, the pretreatment VAS score for duration was 7.4 and the post-treatment score was 3.8. VAS scores for loudness reduced from 6.7 to 5.1 following treatment, and VAS scores for annoyance reduced from 6.5 to 5.0 with treatment. VAS scores for difficulty in activities of daily living decreased from
Table III. Comparison of changes in visual analog scale (VAS) score and tinnitus handicap inventory (THI) score between electrical stimulation and sham stimulation. Assessment VAS
Subscale Duration
Loudness
THI
Group
Prestimulation
Post-stimulation
p value
TENS
6.9 ± 1.6
5.6 ± 2.1
< 0.05*
Sham
6.5 ± 1.2
6.1 ± 1.5
> 0.05
TENS
6.7 ± 1.7
5.8 ± 1.9
< 0.05*
Sham
6.2 ± 1.9
5.6 ± 1.6
> 0.05
Annoyance
TENS
6.7 ± 1.5
5.4 ± 2.2
< 0.05*
Sham
6.5 ± 1.7
5.7 ± 2.2
> 0.05
Difficulty in activities of daily life
TENS
6.8 ± 1.9
5.4 ± 1.9
< 0.05*
Sham
6.6 ± 1.7
6.5 ± 1.3
> 0.05
Functional
TENS
46.3 ± 20.7
45.4 ± 15.9
> 0.05
Sham
43.8 ± 13.1
49.5 ± 11.7
< 0.05*
TENS
50.2 ± 21.5
31.9 ± 17.3
< 0.05*
Emotional
Sham
42.1 ± 15.6
40.5 ± 15.5
> 0.05
Catastrophic
TENS
51.6 ± 21.7
37.4 ± 16.1
< 0.05*
Sham
47.7 ± 13.9
46.2 ± 13.3
> 0.05
Total
TENS
49.4 ± 9.9
42.8 ± 8.7
< 0.05*
Sham
44.5 ± 6.5
45.2 ± 7.9
> 0.05
Results are given as mean ± standard deviation. TENS, transcutaneous electrical stimulation. *p < 0.05.
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Table IV. Treatment results according to tinnitus frequency. Low-frequency tinnitus Assessment
Subscale
Visual analog scale Duration
Loudness
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Annoyance
High-frequency tinnitus
Group Prestimulation Post-stimulation p value
Prestimulation Post-stimulation p value
TENS
7.4 ± 1.7
3.8 ± 1.5
< 0.05*
6.5 ±1.2
6.0 ± 1.3
> 0.05
Sham
5.7 ± 1.2
5.4 ± 1.7
> 0.05
7.0 ± 1.0
6.5 ± 1.3
> 0.05
TENS
6.7 ± 1.5
5.1 ± 1.9
< 0.05*
7.2 ± 1.4
7.0 ± 1.1
> 0.05
Sham
6.3 ± 2.2
5.4 ± 1.7
> 0.05
7.1 ± 1.8
6.7 ± 1.7
> 0.05
TENS
6.5 ± 1.5
5.0 ± 2.2
< 0.05*
7.1 ± 1.7
5.8 ± 1.5
< 0.05*
Sham
6.4 ± 2.1
6.5 ± 1.2
> 0.05
6.5 ± 1.6
6.2 ± 2.5
> 0.05
6.6 ± 1.9
5.3 ± 1.9
< 0.05*
7.1 ± 1.1
5.7 ± 1.7
< 0.05*
Difficulty in activities TENS of daily life Sham
7.2 ± 2.0
7.0 ± 1.1
> 0.05
7.2 ± 1.5
6.2 ± 1.4
> 0.05
Tinnitus Handicap Functional Inventory
TENS
49.4 ± 20.7
47.0 ± 17.4
< 0.05*
47.9 ± 13.0
45.0 ± 12.1
> 0.05
Sham
42.0 ± 17.0
43.8 ± 13.8
> 0.05
44.8 ± 11.1
51.8 ± 9.9
< 0.05*
Emotional
TENS
54.4 ± 21.7
28.7 ± 15.2
< 0.05*
45.9 ± 14.7
32.2 ± 12.3
< 0.05*
Sham
51.5 ± 17.6
48.4 ± 15.5
> 0.05
42.4 ± 15.2
41.6 ± 16.1
> 0.05
Catastrophic
TENS
53.5 ± 20.5
38.0 ± 17.3
< 0.05*
49.5 ± 17.5
35.5 ± 13.2
< 0.05*
Sham
53.7 ± 16.7
48.7 ± 16.7
> 0.05
49.8 ± 12.4
44.8 ± 11.6
> 0.05
Total
TENS
51.8 ± 10.1
39.9 ± 9.1
< 0.05*
47.7 ± 11.4
37.1 ± 9.8
> 0.05
Sham
52.4 ± 16.7
53.6 ± 10.4
> 0.05
45.7 ± 5.8
46.1 ± 6.5
> 0.05
Results are given as mean ± standard deviation. TENS, transcutaneous electrical stimulation. *p < 0.05.
6.6 to 5.3 after treatment. All changes in VAS scores were statistically significant (p < 0.05). For THI scores, whole subscales showed significant improvement after treatment and total THI scores also decreased significantly after treatment (Table IV). In the electrical stimulation group with highfrequency tinnitus, VAS scores for all subscales improved following electrical stimulation, but only two items – annoyance and difficulty in activities of daily life – exhibited statistically significant decreases. Mean total THI score changed from 47.7 to 37.1 with treatment. Functional subscale score decreased from 47.9 to 45.0, emotional stress score changed from 45.9 to 32.2, and catastrophic subscale score decreased from 49.5 to 35.5. All THI scores decreased, but only improvements in emotional stress and catastrophic subscales were statistically significant (Table IV). To analyze the association between degree of hearing disturbance and effect of electrical stimulation, patients in the electrical stimulation group were divided into five subgroups of hearing disturbance: normal, mild, moderate, moderately severe, and severe, according to ISO classification. VAS and THI scores before and after electrical stimulation were calculated. Clinical improvement following treatment for all five hearing level subgroups was compared. In the normal-hearing level group, all VAS subscales and THI scores showed significant improvements. The mild hearing disturbance
group also showed statistically significant improvements inallsubscalesexceptVASscorefordifficultyinactivities of daily life. However, in the severe hearing disturbance group, only the VAS score for difficulty in activities of daily life decreased significantly (Figures 2 and 3). The degree of hearing disturbance and frequency of tinnitus were analyzed simultaneously with multi-way ANOVA, and the statistical value of the difference in the VAS and THI scores according to treatment was compared. The actual therapeutic effect of electrical stimulation on the frequency of tinnitus and degree of hearing disturbance was analyzed with multi-way ANOVA. The interactions among the three variables (treatment arm, frequency of tinnitus, and degree of hearing disturbance) with the changes in the VAS and THI scores were not significant (treatment arm – frequency of tinnitus: p = 0.770, p = 0.070; treatment arm – degree of hearing disturbance: p = 0.395, p = 0.822; frequency of tinnitus – degree of hearing disturbance: p = 0.542, p = 0.860). With multi-way ANOVA, changes in the VAS and THI scores were significantly different between electrical stimulation and sham stimulation (p = 0.046, p = 0.017), and changes in the THI scores between patients with lowand high-frequency tinnitus were significantly different (p = 0.048). Moreover, the change in the THI score was significant according to the degree of hearing disturbance (p = 0.048) (Table V).
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*
8
6
Pre Post
4 2
6
ML Mod MS Change of awareness
4
Se
NL
10
ML Mod MS Change of loudness
Se
10 * *
*
6
Pre Post
4
*
8
*
2
VAS score
VAS score
Pre Post
0 NL
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*
*
2
0
8
*
*
VAS score
VAS score
8
6
Pre Post
4 2
0
0 NL
ML Mod MS Change of annoyance
Se
NL
ML Mod MS Change of effect on life
Se
Figure 2. Change in visual analog scale (VAS) score according to degree of hearing disturbance following electrical stimulation. ML, mild; Mod, moderate; MS, moderate-severe; NL, normal; Pre, pretreatment; Post, after treatment; Se, severe. *p < 0.05.
Considering the results of the study, actual TENS, low-frequency tinnitus, and normal hearing/mild hearing disturbance were associated with significant changes in the THI score.
Improvement in duration of tinnitus after electrical stimulation Duration of tinnitus suppression varied from a few hours to several months. To summarize, 14 patients (31%) received symptomatic relief for less than 1 week and 16 patients (36%) had benefits lasting less than 1 month. Only two patients (4%) had effects lasting longer than 3 months – of note, these two patients had low-frequency tinnitus and mild hearing loss.
Side effects of TENS Mild side effects were seen in eight patients including four patients with dizziness, three patients with headache, and one patient with facial numbness. However, side effects dissipated after cessation of treatment.
Discussion The use of electrical currents to alter physiologic responses has been recognized since the 1800s, and electrical stimulation has been used to treat inflammation, pain, edema, joint dysfunction, and spinal disorders [11,12]. Electrical stimulation for the treatment of tinnitus remains an intriguing therapeutic option. Interestingly, reduction in tinnitus symptoms has been reported as a beneficial side effect following cochlear implantation [4]. In 1977, Graham and Hazell [5] demonstrated tinnitus suppression in two of nine patients via transtympanic stimulation of the promontory with alternating currents. In 1979, Portmann et al. [13] reported an 87% success rate of temporary suppression of tinnitus by electrical stimulation. TENS for tinnitus was reported by Chouard et al. [14] in 1981, with greater than onethird of patients experiencing significant reduction in tinnitus symptoms. Engelberg and Bauer [9] in 1985 reported an 82% improvement in tinnitus symptoms with TENS in a sample of 20 patients. Recent evidence demonstrated a success rate of roughly 50% in 500 patients with tinnitus of varying etiology using electrical stimulation [8]. However, given the
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TENS for tinnitus 100
100
80
80
60
*
* Pre Post
40
THI score
THI score
*
20
ML Mod MS Functional subscale
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60
Pre Post
40
Se
NL
100
ML Mod MS Se Emotional subscale
100
80
80 *
*
Pre Post
40 20
THI score
* THI score
*
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20
0
60
*
* 60
* Pre Post
* 40 20
0
0 NL
ML Mod MS Se Catastrophic subscale
NL
ML
Mod Total THI
MS
Se
Figure 3. Change in Tinnitus Handicap Inventory (THI) score according to degree of hearing disturbance following electrical stimulation. ML, mild; Mod, moderate; MS, moderate-severe; NL, normal; Pre, pretreatment; Post, after treatment; Se, severe. *p < 0.05.
subjective nature of tinnitus, evaluation of treatment efficacy remains difficult. In this study, we evaluated the efficacy of TENS in the management of tinnitus through the use of VAS and THI questionnaires – validated and widely used methods for assessing the impact of tinnitus on daily life. Not surprisingly, conflicting results of electrical therapy for tinnitus have been reported, as many Table V. Statistical value of change in visual analog scale (VAS) score and Tinnitus Handicap Inventory (THI) score analyzed by multi-way ANOVA. p value Change in VAS score
Change in THI score
TENS vs sham procedure
0.046*
0.017*
Low-frequency tinnitus vs high-frequency tinnitus
0.219
0.048*
Degree of hearing disturbance
0.492
0.049*
Factor
*p < 0.05.
factors can influence treatment efficacy including currency of the electrical stimulation and location of stimulation [15]. Currency of the electrical stimulation may be important; however, no clear superiority between direct and alternating currents on tinnitus suppression has emerged. While direct current seems more effective in cochlear stimulation, this method of electrical stimulation should only be employed in patients with severe hearing loss due to the possibility of cochlear damage. Hazell et al. [16] demonstrated that electrical suppression of tinnitus is frequency dependent, with low-frequency stimuli being more effective. The authors concluded that frequency characteristics of tinnitus suppression and auditory discomfort are divergent phenomena at low frequencies, and frequencies higher than 100 Hz should be avoided. The application site of electrical stimulation remains a topic for continued study. Some evidence indicates that electrical stimulation should be administered close to cochlear neurons. Kuk et al. [17]
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reported a reduction in tinnitus in 50% of patients using alternating current via the eardrum. Vernon and Fenwick [18] used preauricular and postauricular electrical suppression of tinnitus in 50 patients and found decreases in tinnitus intensity in 28% of patients as compared with only 2% of patients receiving placebo stimulation. Similarly, in a large caseseries, Steenerson and Cronin [8] used preauricular stimulation and reported a 53% success rate in tinnitus reduction. Based on the aforementioned results, we used a stimulator that generates an alternating current with a frequency of 50 Hz, a level that has previously been reported as most effective for tinnitus suppression. Current intensity was 15 mA, and there were no complications. The placebo effect is often difficult to assess; however, in the present study, electrical stimulation was inaudible and produced no sensation, allowing for blind testing. In addition, we analyzed several variables between the electrical stimulation group and the sham stimulation group. There were no significant differences between the two groups; therefore, we believe that sham stimulation played a role as a true control. As expected, the number of patients who benefited from therapy was higher in the electrical stimulation group than in the sham testing group. We also evaluated the relationships among treatment efficacy, hearing level, and tinnitus frequency. Here, patients with low-frequency tinnitus were more susceptible to electrical stimulation. It has been demonstrated previously that outer hair cell motility increases in response to electrical stimulation. Electrically stimulated outer hair cells can provide inputs to the basilar membrane that, in turn, can excite inner hair cells and elicit synaptically mediated long-latency responses of the auditory nerve and main superior olivary nuclei [19]. According to the tonotopicity of the superior olivary complex, hair cells that respond to low frequency are located ventrolaterally, and hair cells that respond to high frequency are found dorsomedially [20]. Following transcutaneous stimulation, hair cells located more laterally could react faster than at other sites. Therefore, patients with lowfrequency tinnitus may experience better therapeutic effects. Our results suggest that TENS can be effective for tinnitus of various hearing levels as the degree of tinnitus suppression was not significantly different between hearing levels. The site of and mechanism by which electrical stimulation produces tinnitus relief remain unclear. Further research is necessary to determine optimal conditions for electrical stimulation in treating tinnitus.
Conclusions Approximately 62% of patients suffering from tinnitus experience considerable symptomatic relief following TENS. While tinnitus does not completely dissipate, distressing features of tinnitus often disappear with electrical stimulation. Electrical stimulation appears more effective in patients with low-frequency tinnitus or mild hearing loss. Electrotherapy can be repeated without notable risks. Large-scale application of this treatment modality may be helpful to better characterize the underlying mechanisms of tinnitus. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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