[Audiological characteristics of auditory neuropathy].

OBJECTIVE: To study the auditory electrophysiological characteristics of the auditory neuropathy. METHODS: Ten patients were diagnosed as auditory neuropathy. The history, pure tone audiometry, stapedial reflex, auditory brainstem response, electrocochleogram, distortion product otoacoustic emission and his contralateral suppression of white noise, middle latency response and slow cortical response were assessed. Five patients were investigated with brain CT or MRI. RESULTS: The patients were of both genders. The average age was 20.3 years old and most of them were teenagers. Nine patients complained of bilaterally hearing impairment, while one patient who did not complain of hearing loss had a tinnitus of both ears. The pure tone audiogram showed a middle or moderate sensorineural hearing loss at low frequencies 0.5 kHz and/or 0.25 kHz in nineteen ears but a normal audiogram in one ear. Stapedial reflex was absent in nineteen ears, and threshold elevated in one ear while his pure tone audiogram revealed an ascending curve. Auditory brainstem response cannot be recorded or only wave V or/and wave I presented. All of the patients were evoked a distortion product OAE, which cannot be suppressed by contralateral white noise. Electrocochleogram demonstrated AP absent or very small amplitude in most ear and the--SP amplitude were 0.595 microV, while they had a normal slow cortical response but except one patient presented normal middle latency response. The findings of CT or MRI were normal. CONCLUSION: The pure tone audiogram could preserve unchanged at early stage of auditory neuropathy, but their stapedial reflex and auditory brainstem response are absent or threshold elevated. The precise pathologic site of this disorder is yet to be defined, but it may locate in the auditory system below brainstem.