Study Of Auditory Electrophysiological Characteristics Of Auditory Neuropathy

Objective:To analyze the characteristic of pure-tone auditory threshold, distortion product otoacoustic emission and the SP-AP compound potential of auditory neuropathy (AN) patients. Investigate the location of lesion and the pathogenesy of auditory neuropathy.Methods:11 patients (21 ears) with a diagnosis of AN in ENT department of PLA General Hospital were involved in the study, among which 20 ears successfully evoked compound action potential were taken in the AN group. 10 normal-hearing volunteers(20 ears)were taken in the control group.All cases were taken routine examinations about pure tone audiometry, distortion product otoacoustic emission and ECochG, which was recorded from ear canal electrode. The amplitude of DPOAE, peak-latency, amplitude and the time course of the SP-AP compound potential were measured in an 'assessor-blind' study. The correlation between pure tone audiometry and DPOAE at each frequency and the discrepancy of the data in two groups were analyzed with statistical method by the software SPSS for Windows Ver 11.5.Results:Pure tone audiograms of all 20 ears in AN group shew low-frequency hearing loss, 17 among which took on ascent threshold curve while the other 3 display flat curve. The hearing loss at low frequency(250Hz,500Hz,1000Hz) were more than 40 dB in most ears. Distortion product otoacoustic emission of all cases were pass. The average amplitude of each frequency was no significance difference compared with control group. There were contradiction between pure tone threshold and distortion product otoacoustic emission. There were unrepresentative waveform of SP-AP compound potential in AN group: the -SP dominance and multi-peak SP appeared; the amplitude of both AP were lower and -SP were higher than control group; 1/3 wide of the SP-AP compound wave longer than control group.Conclusions:There is no damage in OHCs'function of AN patients. The increasing time-course, higher SP amplitude, lower AP amplitude, dominant and multi-peak SP are typical characteristic in audiology. The location of lesion of auditory neuropathy may be in the cochlear afferent pathway. The asynchronization of the cochlear afferent nerve fibers is one etiopathogenisis of auditory neuropathy.