Prevalence of auditory neuropathy in high risk infants

Auditory neuropathy (AN) or auditory dys-synchrony has been a well-accepted pathology during the last decade. It is characterized by normal outer hair cells function, severely disturbed neural transmission through auditory pathways and a variety of behavioral findings, ranging between near-normal hearing to profound hearing loss. Though we are able to diagnose AN reliably, little is known concerning its epidemiology, etiology and prognosis. This study is aimed at presenting prevalence rates found in a large population consisting of high risk neonates. Between 1995 and 2001, 745 high risk neonates had their hearing tested by ABR. Otoacoustic emissions were also recorded in all cases with abnormal ABR results. Admittance measurements and imaging studies were performed when needed. Children with abnormal ABR findings were scheduled for re-examination after 4-6 months. One hundred twenty-four neonates failed their first ABR test, either monaurally or bilaterally. A subgroup of 54 babies demonstrated ABR threshold >= 80dBHL. Among them otoacoustic emissions were recorded in 19 infants (15.3%), fitting the AN pattern. AN is not as rare pathology as we thought previously. Especially in neonates with high risk factors for hearing loss the prevalence of AN may reach considerable rates. In this study AN was diagnosed in 2.5% of the total HR population. From a practical point of view, these findings suggest that hearing screening protocols for HR neonates may be revised in terms of their methodology.