Effect of hearing loss in electrocochleographic investigation of endolymphatic hydrops using tone-pip and click stimuli.

Extratympanic electrocochleography (ECochG) was performed on 37 patients referred to the Evoked Potential Clinic with suspected Ménière's disease. The patients were classified according to their hearing impairment and audiometric configuration. Click and tone-pip stimuli with tone frequencies of 1 and 4 kHz were presented at a rate of 10 per second. Amplitude, latency and general waveform characteristics of the summation potential (SP) and action potential (AP) were analysed for each averaged response with respect to the level and configuration of the hearing loss. The highest incidence of abnormal percentage SP was in patients with average hearing loss in the range of 40-64 dB HL using the click stimulus. In low tone hearing loss, hydrops was identified from an enhanced SP in significantly more patients using the click and 4 kHz tone-pip than the 1 kHz stimulus. Measurement of the width of the 1 kHz tone-pip response waveform was abnormal in some patients even though the click and 4 kHz responses were normal. The optimum stimulus for identification of hydrops from an enhanced SP is dependent on the level and configuration of the hearing loss.