Tinnitus is defined as an auditory illusion or a phantom sound sensation that occurs in the absence of external auditory stimuli, indicating the perception of sound without any objective sound source (ANSI, 1969). Tinnitus is a symptom that can have adverse effect on quality of life leading to depression and somatization disorders. Irrespective of its origin, tinnitus is considered in the auditory cortex. The incidence of tinnitus worldwide in adult subjects has been mentioned to be 10% to 15%.¹

Tinnitus can be linked to dysfunction at any auditory pathways level, however, it usually initiates in the cochlea. It has been reported that stimulus is usually started in the cochlea which result in abnormal activity in central pathway finally helping in symptom maintenance. Various studies have assessed any existing link in tinnitus and impairment of efferent auditory system by assessing the suppression of OAEs (otoacoustic emissions). The findings reports that even mild cochlear function variation can be seen via OAE testing before significant changes seen in the audiogram of the subjects. Hence, analysis of OAEs and their suppression is vital and is progressively crucial for differential diagnosis of disorders leading to tinnitus.²

Various efforts are being made to judge the mechanism of the tinnitus, especially concerning the cochlear function. Spontaneous OAEs (otoacoustic emissions) have been usually reported in studies related to the tinnitus. Different studies have reported that transient distortion product otoacoustic emissions (DPOAEs) and transient evoked otoacoustic emissions (TEOAEs) can act as effective ways for detection of hearing loss even in cases where such loss is not seen on audiogram. However, few studies on OAEs concerning tinnitus report inconsistent results, whereas, other studies have reported diminished DPOAE or TEOAE in subjects with tinnitus, other studies supported increased amplitude for DPOAE or TEOAE in subjects with tinnitus. This suggest that OAE results associated with tinnitus shows change in function of OHC (outer hair cell).³

Other assessment assessed cochlear function, especially the role of inner hair cells in tinnitus, is TEN (Threshold Equalizing Noise) test. Identical to OAE results, the findings of TEN have also been contradictory in the literature for tinnitus subjects. One study in literature reported cochlear dead regions in majority of subjects with tinnitus. Other studies gave reported dead region in few subjects only with tinnitus. Also, other studies have reported significant raised threshold in TEN tests in tinnitus subjects with normal hearing and no dead regions.⁴ The present study was aimed to evaluate the cochlear function in subjects with tinnitus independent of their hearing status.

The present clinical study was aimed to evaluate the cochlear function in subjects with tinnitus independent of their hearing status. The study subjects were from Department of ENT of the Institute. Verbal and written informed consent were taken from all the subjects before study participation. The study included subjects with minimum 6 months of tinnitus in at least one ear. The present study assessed 80 subjects that had tinnitus and were categorized in the two groups where Group I had 40 subjects that had tinnitus with hearing loss and Group II had 40 subjects with tinnitus and no hearing loss. Another 40 subjects formed control group including 40 subjects with hearing loss and no tinnitus. There were 26 males and 14 females in Group I, 22 males and 18 females in Group II, and 20 males and females each in control group. The mean age of the study subjects in Group I, II, and control was 43.4±2.5, 41.6±3.4, and 42.4±1.6 years respectively. The exclusion criteria for the study were subjects with conductive hearing loss, history of ear surgery, pulsatile tinnitus, temporomandibular joint disorders, psychological issues, neurological disorders, retrocochlear pathology, and subjects with tympanogram other than A type (like As type, Ad type, B type, C type). Level of discomfort with tinnitus was assessed with Tinnitus Handicap Inventory. For audiological assessment, extensive anamnesis was done in all the subjects. Air-conduction thresholds were recorded in frequency range of 125-8,999 Hz using TDH-39 headphones, whereas, while bone-conduction thresholds were measured from 500 to 4,000 Hz using a B71 bone vibrator. To assess tinnitus, background was assessed for identification of tinnitus localization. To establish pitch and frequency of tinnitus, Vernon technique was used. In this procedure, subjects were exposed to two sounds of varying frequencies as F1 and F2 where F1<F2 and asked to asses which sound is closer to tinnitus. Considering match of loudness, subjects were presented with sounds that fall in tinnitus frequency range. After establishing feedback if sound is soft or loud, range is refined for identification closest loudness level. Evaluation generally started with ear that is more severely affected in bilateral tinnitus, however, if tinnitus was equal in both ears, left ear is first assessed. For unilateral tinnitus, only affected ear was assessed. If subject described tinnitus as perceived in centre of head, these are considered as bilateral tinnitus. To assess discomfort level the Greek version of the Tinnitus Handicap Inventory (THI) was utilized. The THI had 25 items where each had three possible responses and total score was used to assess discomfort linked with tinnitus. TEN (Threshold Equalizing Noise) test was done in all subjects at frequencies of 500, 1000, 2000, and 4000 Hz using a Grason Stadler (GSI) Audio Star Pro audiometer along with TDH39 headphones. In bilateral tinnitus cases, TEN was done in both the ears, whereas, for unilateral tinnitus, only affected ear was assessed. TEN level was assessed following the hearing thresholds of the subjects, as described by Brian Moore et al in 2007.5 For hearing threshold better than 25dB, TEN was set at 50 dB to avoid false positive responses and for thresholds 25-60dB, TEN was adjusted to 70 dB, and for thresholds worse than 60dB, Ten was set 10dB above threshold. Maximum TEN adjustment did not exceed 90dB owing to cochlear sensitivity.6 Also, it has been reported that TEN can be done at varying severity levels.7,8 In Otoacoustic Emission Tests, TEOAE and DPOAE assessments were done using Autodynamics EZ Screen. TEOAEs were evaluated in ears with tinnitus in quick screen mode, applying a 260 sweep at an intensity of 84 dB SPL for 80 milliseconds. The TEOAEs were recorded at frequencies of 1000 Hz, 1414 Hz, 2000 Hz, 2828 Hz, and 4000 Hz, capturing both the signalto-noise ratios (SNR) and the amplitudes of the responses. Concerning DPOAEs, SNRs amplitude were recorded at 1001, 2002, 3003, 4004, 6006, and 7996 Hz frequencies using 2fl-f2 ratio and L1/L2 intensity levels of 65/55 dB SPL, with an average of 500 sweeps conducted. Statistical analysis of the gathered data was done using chi-square test, Fisher’s exact test, Mann Whitney U test, and SPSS (Statistical Package for the Social Sciences) software version 24.0 (IBM Corp., Armonk. NY, USA) using ANOVA, chi-square test, and student's t-test. The significance level was considered at a p-value of <0.05.

The present clinical study was aimed to evaluate the cochlear function in subjects with tinnitus independent of their hearing status. The study included 62 subjects with 32 subjects of 14 females and 18 males having both hearing loss and tinnitus were included in Group I, 30 subjects with 12 females and 18 males had tinnitus alone and formed Group II, and 42 subjects of 24 females and 18 males were in control group that neither had hearing loss or tinnitus. The mean age of the study subjects in Group I, II, and control was 43.4±2.5, 41.6±3.4, and 42.4±1.6 years respectively. THI scores reported a discomfort level of 1-5 in both groups I and II and no significant difference in two groups with p=0.12.

It was seen that in Group II subjects, tinnitus frequency showed variations with mainly affecting higher frequencies of 4-12 kHz. On the contrary, in Group I, tinnitus was mainly assessed at frequencies linked to hearing loss. Configurations of hearing loss were categorized as sloping, flat, and notch at 6kHz in 22, 8, and 12 subjects respectively. Mild, moderate, and severe hearing loss was reported in 6, 8, and 10 study subjects respectively. In remaining study subjects, PTA was normal, however, sensorineural hearing loss was seen at higher frequencies. For medical history, it was noted that no hearing loss was congenital and no chronic disease was seen (Table 1).

The study results showed that for TEN test, criteria for identifying a differential response (DR) required the masked threshold to be at least 10 dB lower than the unmasked threshold. The study assessed threshold alterations in the presence of tonal masking noise (TEN) across all frequencies. In both control group and group II, no subject showed DR, whereas, in Group I, DR was seen in 4 subjects with bilateral sensorineural hearing loss and tinnitus, all raised thresholds under TN and other two subjects had moderately severe sensorineural hearing loss and tinnitus, showing DRs bilaterally at 0.5 kHz, 1 kHz, and 4 kHz.

It was also seen that for OAE, in assessing DPAOE and TEOAE, both emission response amplitudes and the signal-to-noise ratio (SNR) were assessed. Owing to hearing loss in Group I subjects, either no OAE response or minimal OAE amplitudes were seen with amplitude range of −12.5 to 8.6 dB. Further, on comparing Group II and control group, no significant difference was seen in amplitude and SNR at frequencies of 1000 Hz, 1414 Hz, 2228 Hz, and 4000 Hz between in control group and Group II. For SNRs in DPOAE, results were comparable to TEOAE with no significant difference in control group and Group II at frequencies of 1, 1.5, 2, 3, and 4 kHz. However, emission response at 6 kHz and 8 kHz were significantly reduced in group II with p-values of 0.03 and 0.01 respectively.

Table 1: Demographic and clinical picture of the study subjects

Table 2: Change level in group threshold concerning TEN noise exposure

The present study assessed 62 subjects with 32 subjects of 14 females and 18 males having both hearing loss and tinnitus were included in Group I, 30 subjects with 12 females and 18 males had tinnitus alone and formed Group II, and 42 subjects of 24 females and 18 males were in control group that neither had hearing loss or tinnitus. The mean age of the study subjects in Group I, II, and control was 43.4±2.5, 41.6±3.4, and 42.4±1.6 years respectively. THI scores reported a discomfort level of 1-5 in both groups I and II and no significant difference in two groups with p=0.12. These data were comparable to the previous studies of Lobarinas E et al9 in 2013 and Starr A et al10 in 2003 where authors assessed subjects with tinnitus and data comparable to the present study in their studies.

The study results showed that in Group II subjects, tinnitus frequency showed variations with mainly affecting higher frequencies of 4-12 kHz. On the contrary, in Group I, tinnitus was mainly assessed at frequencies linked to hearing loss. Configurations of hearing loss were categorized as sloping, flat, and notch at 6kHz in 22, 8, and 12 subjects respectively. Mild, moderate, and severe hearing loss was reported in 6, 8, and 10 study subjects respectively. In remaining study subjects, PTA was normal, however, sensorineural hearing loss was seen at higher frequencies. For medical history, it was noted that no hearing loss was congenital and no chronic disease was seen. These results were consistent with the findings of Kara E et al11 in 2020 and Marmel F et al12 in 2020 where tinnitus frequency results comparable to the present study were also reported by the authors in their studies.

It was seen that for TEN test, criteria for identifying a differential response (DR) required the masked threshold to be at least 10 dB lower than the unmasked threshold. The study assessed threshold alterations in the presence of tonal masking noise (TEN) across all frequencies. In both control group and group II, no subject showed DR, whereas, in Group I, DR was seen in 4 subjects with bilateral sensorineural hearing loss and tinnitus, all raised thresholds under TN and other two subjects had moderately severe sensorineural hearing loss and tinnitus, showing DRs bilaterally at 0.5 kHz, 1 kHz, and 4 kHz. These findings correlated with the results of Granjeiro RC et al13 in 2008 and Buzo BC et al14 in 2014 where TEN results reported by the authors were comparable to the results of the present study.

The study results also showed that for OAE, in assessing DPAOE and TEOAE, both emission response amplitudes and the signal-to-noise ratio (SNR) were assessed. Owing to hearing loss in Group I subjects, either no OAE response or minimal OAE amplitudes were seen with amplitude range of −12.5 to 8.6 dB. Further, on comparing Group II and control group, no significant difference was seen in amplitude and SNR at frequencies of 1000 Hz, 1414 Hz, 2228 Hz, and 4000 Hz between in control group and Group II. For SNRs in DPOAE, results were comparable to TEOAE with no significant difference in control group and Group II at frequencies of 1, 1.5, 2, 3, and 4 kHz. However, emission response at 6 kHz and 8 kHz were significantly reduced in group II with p-values of 0.03 and 0.01 respectively. These results correlated with the findings of Ami M et al15 in 2008 and Weisz N et al16 in 2006 where OAE results comparable to the present study were also reported by the authors in their studies.

Considering its limitations, the present study concludes that conventional methods of testing suits for evaluation of tinnitus subjects that have hearing loss. Also, in subjects with normal hearing and tinnitus, using additional methods as Tone-Evoked Noise (TEN) and Otoacoustic Emissions (OAE) enable a more accurate assessment of peripheral hearing mechanisms. No or limited otoacoustic emissions (OAEs) seen in Group I showed a potential decrease or function loss in OHC (outer hair cells) at a particular frequency. On the contrary, increased threshold of tone-equalizing noise (TEN) test points to possible dysfunction in IHC (inner hair cells).

1. Thabet EM (2009) Evaluation of tinnitus patients with normal hearing sensitivity using TEOAEs and TEN test. Auris Nasus Larynx 2009;36:633–636
2. Weisz N, Moratti S, Meinzer M, Dohrmann K, Elbert T (2005) Tinnitus perception and distress is related to abnormal spontaneous brain activity as measured by magnetoencephalography. PLoS Med 2005;2:e153
3. Jastreboff PJ (1990) Phantom auditory perception (Tinnitus). Mechanisms of generation and perception. Neurosci Res 1990;8: 221–54
4. Shailer MJ, Tyler RS, Coles RRA (1981) Critical masking bands for sensorineural tinnitus. Scand Audiol 1981;10:157–162.
5. Fabijańska A, Smurzyński J, Hatzopoulos S, Kochanek K, Bartnik G, Raj-Koziak D, Skarżyński H. The relationship between distortion product otoacoustic emissions and extended high-frequency audiometry in tinnitus patients. Part 1: normally hearing patients with unilateral tinnitus. Med Sci Monit 2012;18:CR765.
6. Thabet EM (2009) Evaluation of tinnitus patients with normal hearing sensitivity using TEOAEs and TEN test. https://doi.org/1 0.1016/j.anl.2009.01.002. Auris Nasus Larynx
7. Kowalska S, Sułkowski W (2001) Tinnitus in noise-induced hearing impairment. Med Pr 2001;52:305–313
8. Ami M, Abdullah A, Awang MA, Liyab B, Saim L (2008) Relation of distortion product otoacoustic emission with tinnitus. Laryngoscope 2008;118:712–717.
9. Lobarinas E, Salvi R, Ding D (2013) Insensitivity of the audiogram to carboplatin induced inner hair cell loss in Chinchillas. Hear Res 2013;302:113–120.
10. Starr A, Michalewski HJ, Zeng FG, Fujikawa-Brooks S, Linthicum F, Kim CS, Keats B (2003) Pathology and physiology of auditory neuropathy with a novel mutation in the MPZ gene (Tyr145Ser). Brain 2003;126:1604–1619.
11. Kara E, Aydın K, Akbulut AA, Karakol SN, Durmaz S, Yener HM, Kara H (2020) Assessment of hidden hearing loss in normal hearing individuals with and without tinnitus. J Int Adv Otol 2020;16:87.
12. Marmel F, Cortese D, Kluk K (2020) The ongoing search for cochlear synaptopathy in humans: masked thresholds for brief tones in threshold equalizing noise. Hear Res 2020;392:107960.
13. Granjeiro RC, Kehrle HM, Bezerra RL, Almeida VF, Sampaio AL, Oliveira CA (2008) Transient and distortion product evoked oto-acoustic emissions in normal hearing patients with and without tinnitus. Otolaryngol Head Neck Surg. 2008;138:502–506
14. Buzo BC, Carvallo RMM (2014) Psychoacoustic analyses of cochlear mechanisms in tinnitus patients with normal auditory thresholds. Int J Audiol. 2014;53:40–47.
15. Ami M, Abdullah A, Awang MA, Liyab B, Saim L (2008) Relation of distortion product otoacoustic emissions with tinnitus. Laryngoscope. 2008;118:712–717
16. Weisz N, Hartmann T, Dohrmann K, Schlee W, Norena A (2006) High-frequency tinnitus without hearing loss does not mean absence of deafferentation. Hear Res 2006;222:108–114.