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Abstract
The study aimed at understanding the psychoacoustic characteristics of tinnitus in individuals with auditory neuropathy spectrum disorder (ANSD). It attempts to assess the pitch and intensity of loudness of tinnitus matched by individuals with ANSD. Fifty individuals who were diagnosed as having auditory neuropathy spectrum disorder were included in the study. Tinnitus evaluation was carried out where the individuals matched the frequency and intensity of loudness of the tinnitus. The results of the study shows that pitch matched by majority of patients with ANSD is predominantly low pitched (<1000 Hz). The frequency of tinnitus matched by the patients with ANSD also correlated with the degree of maximal hearing loss. The intensity of loudness of the tinnitus was around 10-15 dB higher than their threshold in majority of the patients considered in the study. There was a weak negative correlation for the matched frequency and intensity of loudness. The results of the study suggest that majority of individuals with low frequency hearing loss had low pitched tinnitus. Thus, there could be discordant damage between outer and inner hair cells, abnormal firing of auditory nerve in individuals with ANSD which can lead to tinnitus. Thus, it can help to understand the physiology of tinnitus in individuals with ANSD.
Highlights
Auditory neuropathy spectrum disorder (ANSD) is a condition in which a patient’s outer hair cells are normal [represented by normal otoacoustic emission (OAE) response/Cochlear microphonics] and an absent/abnormal auditory brainstem response (ABR) with fluctuating hearing loss.[1,2,3,4,5] The cause of ANSD is presumed to be at the inner hair cells, junction of the spiral ganglion cells and/or the auditory nerve[6,7] ANSD is diagnosed based on multiple behavioral and electrophysiologic tests.[8]
The results of the study showed that majority of patients with ANSD had bilateral tinnitus. 86% (43 out of 50) of the patients reported of bilateral tinnitus and 14% (7 out of 50) had unilateral tinnitus
One of the site of lesion reported in individuals with ANSD are inner hair cells (IHC)[3,6,7] and subtle damage at the level of outer hair cells (OHC) with abnormal spontaneous otoacoustic emissions.[22]
Summary
Auditory neuropathy spectrum disorder (ANSD) is a condition in which a patient’s outer hair cells are normal [represented by normal otoacoustic emission (OAE) response/Cochlear microphonics] and an absent/abnormal auditory brainstem response (ABR) with fluctuating hearing loss.[1,2,3,4,5] The cause of ANSD is presumed to be at the inner hair cells, junction of the spiral ganglion cells and/or the auditory nerve[6,7] ANSD is diagnosed based on multiple behavioral and electrophysiologic tests (such as ABR, OAE, acoustic reflexes, word recognition scores, speech perception in noise, etc.).[8]. Literature review suggests that most of the individuals with auditory neuropathy spectrum disorder reported difficulty in understanding speech, and tinnitus was found to be one of the complaints.[10,11,12] Tinnitus is the perception of sound by the listener in the absence of an external sound source.[13] In general population, tinnitus has been reported in approximately 10 to 15% of adults. The prevalence rate increases with age and gender, as more men than women report tinnitus, and in 1 to 2%, tinnitus is severe enough to impair daily life significantly.[14] Tinnitus can be a symptom of a variety of auditory disorders, but exact causal mechanisms are not well understood. The psychoacoustic characteristics cannot be used to determine the severity of tinnitus but may be useful in understanding the pathophysiology and causal mechanism of underlying condition
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