Clinical application of non-invasive electrocochleography.

Non-invasive extratympanic electrocochleography (ECochG) was performed in normal-hearing subjects and patients with sensorineural deafness. Action potential (AP) threshold, N1 input-output function, waveform, summating potential (SP) are presented. AP thresholds were within 15 dB in normal-hearing ears and within 30 dB in hearing-impaired ears above subjective thresholds for the click. Correlational analysis showed that click-evoked AP thresholds are best correlated to pure tone thresholds at 2 to 4 kHz. Four types of N1 input-output functions were classified. Normal functions appeared in moderate high tone loss only at 8 kHz and low tone loss with almost normal threshold above at 4 kHz. Many ears with a flat loss had recruiting responses, while many ears with a high tone loss had either dissociated responses or responses with prolonged latency. Several types of waveforms were distinguished. Enhanced--SP was observed in Meniére's disease and late congenital syphilis to which endolymphatic hydrops is common. The clinical value of the non-invasive ECochG is discussed.