Investigation of clinical features of auditory neuropathy in infants

Objective To analyse the clinical data and audiological characteristics of 12 infants with auditory neuropathy(AN) for gaining a better understanding of the clinical features of auditory neuropathy in infants. Methods The clinical methods used in this study were as follows: (1) audiological examination, including visual reinforcement audiometry(VRA), acoustic immitance testing, distortion product otoacoustic emission (DPOAE), transient evoked otoacoustic emission (TEOAE), auditory brainstem response(ABR), 40 Hz auditory event related potential(40 Hz-AERP), and auditory steady state response (ASSR); (2) auxiliary examination, including high-resolution computed tomography(CT) scan of the temporal bone, assay for vitamin B12 , vitamin M and homocysteic acid. Results The onset age of the 12 infants ranged between 0-2 yr and 8 of whom it was lower than 1yr. Among the 8 patients (15 ears) who underwent VRA testing most (80%) showed severe to profownd deafness. Ten patients (20 ears) underwent acoustic immitance measurements, and the acoustic stapedial reflex was absent in all ears. All the patients had a normal DPOAE or TEOAE, but the ABR was absent or only wave I was present. In addition, the ASSR thresholds were lower, while the 40Hz-AERP thresholds were higher in most infants than subjective hearing threshold. Conclusion The audiological characteristics of auditory neuropathy in infants are different from those in adults and children. The diagnosis of auditory neuropathy in infants is documented by normal DPOAE, absent ABR, and no evidence of retrocochlear lesions in imaging examination. The ASSR and 40Hz-AERP would assist diagnosis. Therefore, OAE should be combined with automated ABR to more effectively diagnose auditory neuropathy in infants.