Abstract
Tinnitus is defined as phantom auditory perception without corresponding acoustic or mechanical correlates in cochlea. Existing evidence on its physiological basis is wide ranging, but its origin is still under exploration. To objectify this subjective phenomenon, Auditory Brainstem response test is used. The primary purpose of our study was to ascertain any significant difference in auditory electrophysiological response parameters in sensorineural hearing loss with tinnitus group when compared to controls (normal hearing subjects). Secondary aim was to find correlation of these parameters with degree of hearing loss and severity of tinnitus. This was a case control study conducted in the department of Otorhinolaryngology in tertiary care hospital, New Delhi over a period of one and half years. The study comprised of one hundred and sixty patients out of which, fifty-five patients were sensorineural hearing loss with tinnitus and fifty-one patients were normal hearing subjects. General medical and audiological assessment was done. Significant increase in latency of wave I, III, V and increase in inter peak latency of I–III, III–V, I–V was observed in tinnitus with sensorineural hearing loss group when compared to controls. It was reported that on increasing degree of hearing loss, there was increase in latency of wave I, III, V and increase in inter peak latency of wave I–III, I–V in the former group.
Keywords: Tinnitus, Sensorineural hearing loss, Auditory brainstem response, Absolute latency, Inter peak latency
Introduction
Tinnitus is defined as a phantom auditory perception—a perception of sound without corresponding acoustic or mechanical correlates in the cochlea [1]. Acoustic, attentional and emotional component of tinnitus interact and influence one another worsening quality of life [2, 3]. Existing evidence on physiological basis of tinnitus is extensive and wide ranging, still, the origin of tinnitus is enigma in the literature. Auditory Brainstem Response test elicits brainstem potentials in response to audiological click stimuli. It aids in objectifying this subjective complaint and identification of electrophysiological correlate for tinnitus [4, 5]. It is a useful tool in investigating anatomical and functional characteristic of auditory pathway. Unravelling the mystery of origin and pathophysiological pathway of tinnitus, will be a boost for treatment research.
Materials and Methods
In the present case control study conducted in Department of Otorhinolaryngology in a tertiary care hospital, one hundred six patients were included out of which, fifty-five patients of sensorineural hearing loss with tinnitus and fifty-one subjects with normal hearing, were enrolled. It was approved by the Ethical Committee of the hospital, New Delhi. The primary aim was to study any significant difference in auditory electrophysiological response parameters in sensorineural hearing loss with tinnitus group when compared to controls (normal population). Secondary aim was to find correlation of electrophysiological parameters with degree of hearing loss and severity of tinnitus. Patients with bilateral sensorineural hearing loss with subjective tinnitus (cases) (age > 18 years or any sex) not under any related treatment (like hearing aids) were included in the present study. While, patients with objective tinnitus, definite middle ear pathology and co morbidities like diabetes mellitus, cardiovascular, neurological, psychiatric dysfunctions were excluded from the study. The normal hearing patients (controls) were patients coming to department for problems other than otological complaints or were attendants of the patients. The age group, sex and socio demographic characteristics of the control was matched according to the cases. An informed written consent was taken from all the participants. All cases were subjected to a panel of general medical assessment to identify tinnitus-related pathologies and co morbidities, which was followed by an audiological history. The cases were asked in detail about characteristics of sound, its severity, any aggravating and relieving factors. Cases scored their severity of tinnitus according to subjective visual analogue scale, where, score 1–3 = mild = 1, 4–6 = moderate = 2, 7–9 = severe = 3, 10 = incapacitating = 4. This was followed by otoscopic and audiological (pure tone audiometry & auditory brainstem response test) examination. Sensorineural hearing loss was classified into mild = 26–40 dB, moderate = 41–60 dB, severe > 61 dB hearing loss (according to WHO criteria). Further, amplitude peak and latency of wave I, III, V and inter peak lately of wave I–III, III–V, I–V was recorded using NEURO AUDIO 2013.
Statistical Analysis
Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± SD and median. Normality of data was tested by Kolmogorov–Smirnov test. If the normality was rejected then non parametric test was used.
Statistical tests were applied as follows:
Quantitative variables were compared using Independent T test/Mann–Whitney Test (when the data sets were not normally distributed) between the two groups.
Qualitative variables were correlated using Chi Square test/Fisher exact test.
Spearman rank correlation coefficient was used to assess the association of various parameters with each other.
A P value of < 0.05 was considered statistically significant.
The data was entered in MS EXCEL spreadsheet and analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0.
Results
In our study, fifty-five patients of tinnitus with sensorineural hearing loss (thirty males and twenty-five females) with and fifty-one normal hearing subjects (twenty-eight males and twenty-three females) were included in the study. The mean age of cases was 42.91 years and of controls was 41.63 years. There was no significant difference between the age, gender and education level of the groups. Results revealed statistically significant difference in latency of wave I (P < 0.0001), wave III (P = 0.0001) and wave V (P < 0.0001) in patients with tinnitus and sensorineural hearing loss as compared to control group (elucidated in Table 1). Also, results showed statistically significant difference in inter peak latency of wave I–III (P = 0.007), III–V (P < 0.0001), I–V (P < 0.001) in patients of tinnitus with sensorineural hearing loss when compared to controls (shown in Table 2). On increasing degree of hearing loss, statistically significant increase in latency of wave I (P = 0.0002), III (P < 0.0001), V (P < 0.0001) was seen in tinnitus with sensorineural hearing loss group (as seen in Graph 1). On increasing degree of hearing loss, statistically significant increase in inter peak latency of wave I–III (P = 0.012), I–V (P = 0.0002) was reported, while no significant change was seen in inter peak latency of III–V (P = 0.336) was seen in tinnitus with sensorineural hearing loss group (as seen in Graph 2). On increasing severity of tinnitus (according to Visual Analogue Scale), no significant relation was seen in wave I, III, V latency or their inter peak latency (as shown in Table 3). Also, Severity of tinnitus has shown direct co- relation with degree of hearing loss, which was found to be statistically significant (P = 0.0001).
Table 1.
There is significant increase in absolute latency values of wave I, III and V in sensorineural hearing loss with tinnitus group in comparison to the normal hearing subjects
| Parameter (Absolute latency) | Controls (51) | Tinnitus with sensorineural hearing loss (55) | P value |
|---|---|---|---|
| Wave I | 1.72 ± 0.06 | 1.93 ± 0.12 | < 0.0001 |
| Wave III | 3.75 ± 0.11 | 3.9 ± 0.21 | 0.0001 |
| Wave V | 5.53 ± 0.17 | 6.01 ± 0.22 | < 0.0001 |
Table 2.
There is significant increase in inter peak latency values of above mentioned waves in sensorineural hearing loss with tinnitus group in comparison to the normal hearing subjects
| Parameter (Interpeak latency) | Controls (51) | Tinnitus with sensorineural hearing loss (55) | P value |
|---|---|---|---|
| Wave I–III | 2.03 ± 0.06 | 1.98 ± 0.19 | 0.007 |
| Wave III–V | 1.78 ± 0.13 | 2.11 ± 0.22 | < 0.0001 |
| Wave I–V | 3.81 ± 0.14 | 4.08 ± 0.19 | < 0.0001 |
Graph 1.
The graph shows significant increase in absolute latency values of wave I, III and V with increasing degree of sensorineural hearing loss in patients of sensorineural hearing loss (SNHL) with tinnitus (P = 0.0002, < 0.0001. < 0.0001 respectively), wherein, mild = 26–40 dB, moderate = 41–60 dB, severe > 61 dB hearing loss
Graph 2.
The graph shows significant increase in interpeak latency values of wave I–III and I–V with increasing degree of sensorineural hearing loss in patients of sensorineural hearing loss (SNHL) with tinnitus (P = 0.012, 0.0002 respectively), wherein, mild = 26–40 dB, moderate = 41–60 dB, severe > 61 dB hearing loss. The relation with III–V was not significant (P = 0.336)
Table 3.
There is no significant change in either absolute latency values of wave I, III and V or the interpeak latency with increasing severity of tinnitus
| Parameter | Mild (13) | Moderate (22) | Severe (16) | Incapacitating (4) | P value |
|---|---|---|---|---|---|
| Wave I | 1.89 ± 0.14 | 1.92 ± 0.12 | 1.96 ± 0.12 | 1.93 ± 0.08 | 0.363 |
| Wave III | 3.86 ± 0.2 | 3.86 ± 0.21 | 3.99 ± 0.21 | 4 ± 0.21 | 0.178 |
| Wave V | 5.95 ± 0.19 | 5.99 ± 0.25 | 6.08 ± 0.2 | 6.09 ± 0.18 | 0.075 |
| Wave I–III | 1.97 ± 0.14 | 1.93 ± 0.23 | 2.02 ± 0.14 | 2.07 ± 0.21 | 0.472 |
| Wave III–V | 2.09 ± 0.11 | 2.13 ± 0.28 | 2.09 ± 0.16 | 2.09 ± 0.32 | 0.713 |
| Wave I–V | 4.06 ± 0.19 | 4.06 ± 0.23 | 4.11 ± 0.14 | 4.16 ± 0.16 | 0.162 |
Discussion
Different pathophysiological mechanisms have been suggested for origin of tinnitus in various studies conducted in past. Still, no conclusive etiology and mechanism can be quoted. Increase in wave I and III latency indicates aberrant neural activity in Cochlear nucleus and Cochlear nerve nucleus complex respectively. Prolongation of wave V latency indicates neural abnormalities at the level of lower brainstem (in Lateral Lemniscus, Inferior colliculus). In our study, we found statistically significant increase in latency values of wave I, III and V in patients with tinnitus and sensorineural hearing loss as compared to control group. Various studies conducted in past support our findings. Rosenhall and Axelson [6] (compared ABR between two groups-normal hearing to mild sensorineural hearing loss having tinnitus with moderate to severe sensorineural hearing loss having tinnitus) found similar findings in tinnitus with moderate to severe sensorineural hearing loss group. Ikner and Hasaan [7], Ravikumar and Murthy [8], Kehrle et al. [9] (compared ABR in tinnitus group with normal hearing group) reported similar findings. Said et al. [10] (compared ABR findings in bilateral mild-moderate degree sensorineural hearing loss with and without tinnitus as opposed to normal hearing subjects) found significant prolongation of wave I, III and V latency in tinnitus patients when compared to controls. Golijanian et al. [11], studied ABR differences between tinnitus patients with and without hearing loss and reported increase in latency of wave I and V in hearing loss group while increase in wave III latency in patients without hearing loss. Singh et al. [12] (ABR comparison in tinnitus with normal hearing population), Milloy et al. [13], found significant increase in latency of wave I. Maurizi et al. [14], found significant difference in latency of only wave V. Our findings are in complete disagreement with Konadath et al. [15], Choudhary et al. [16], where no significant differences were found in absolute latency of any of the three waves between tinnitus and normal hearing group. Increase in inter peak latency (IPL) denotes increase neural conduction time in auditory nerve pathway and brainstem. Increase IPL wave III–V indicates purely brainstem dysfunction. This could be due to permanent activation of auditory system by tinnitus, which might change central transmission at upper brainstem further modifying external stimuli transmission [2]. In our study, we found statistical significant difference in IPL(interpeak latency) wave I–III, III–V, I–V on comparing SNHL with tinnitus group with controls. Rosenhall and Axelson [6], Ikner and Hassan et al. [7], Kehrle et al. [9] found significant increase in IPL III–V suggesting brainstem involvement. Said et al. [10] found increase in IPL III–V and I–V in tinnitus group in females, while increase in IPL III–V only in males. Golijanian et al. [11], reported significant increase in IPL wave I–V in tinnitus patients with hearing loss. Singh et al. [12] found decrease in IPL I–III and I–V, as opposed to our findings. On increasing degree of hearing loss, statistically significant increase in latency of wave I, III, V was seen in tinnitus with sensorineural hearing loss group. On increasing degree of hearing loss, statistically significant increase in inter peak latency of wave I–III, I–V was reported, while no significant change was seen in inter peak latency of III–V was seen in tinnitus with sensorineural hearing loss group. On increasing severity of tinnitus (according to Visual Analogue Scale), no significant relation was seen in wave I, III, V latency or their inter peak latency. Also, severity of tinnitus has shown direct co- relation with degree of hearing loss, which was found to be statistically significant. Changes in ABR in the present study indicates peripheral auditory pathway and central auditory alterations. Hence, ABR is a promising electrophysiological investigation for exploring the origin of tinnitus. This would aid in treatment strategies in tinnitus like trans cranial magnetic stimulation which focuses on the neuro stimulation of specific brain regions potentially involved in the pathophysiology of tinnitus.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical approval
All procedures involving human participants were in accordance with the ethical standards of the institution.
Informed consent
Informed consent was obtained from all individuals participants included in this study.
Footnotes
Publisher's Note
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