Auditory neuropathy spectrum disorder: its prevalence and audiological characteristics in an Indian tertiary care hospital

Objective: Auditory neuropathy spectrum disorder (ANSD) has become a well accepted clinical entity. ANSD has now become easy to recognize with advent of test battery approach for hearing loss evaluation. However, little is known about its epidemiology and aetiology, especially its prevalence and incidence in India. This study was conducted to determine the prevalence and audiological characteristics of ANSD in our tertiary care hospital at New Delhi, India.

Methods: We prospectively enrolled all the paediatric cases i.e. less than 12years of age referred to our outpatient department for hearing evaluation. All the cases were evaluated using complete audiological test battery consisting of pure tone audiometry (PTA), impedance audiometry, acoustic reflexes, otoacoustic emissions (OAE), and brain stem evoked response audiometry (BERA). The instrument used was GSI Audera. BERA with both condensation and rarefaction polarity was performed in cases with absent wave V even at highest intensity levels. The criteria used for diagnosis of ANSD was normal or near normal cochlear hair cells (sensory) function (preservation of otoacoustic emissions and/or cochlear microphonics) and absent or abnormal auditory nerve function (absent or severely abnormal auditory brainstem potentials). A repeat test battery was performed after 3months on the diagnosed cases of auditory neuropathy. Based on their behavioural findings the appropriate management programme was formulated.

Results: A total of 487 paediatric cases were referred for hearing evaluation. 183 (37.6%) cases showed absent BERA and 26(5.3%) cases fulfilled the diagnostic criteria for ANSD. Repeat examination after 3months revealed presence of OAE's in 57.6% (15/26) cases while cochlear microphonics were present in all the 26 cases.

Conclusion: The prevalence of ANSD in our study is 5.3% and in children diagnosed with severe to profound hearing loss is 14%. Presence of cochlear microphonics with absent BERA seems to be reliable criteria for diagnosing ANSD.