Electrocochleography in endolymphatic hydrops using tone-pip and click stimuli.

Abstract

The use of electrocochleography (ECochG) in the identification of endolymphatic hydrops in Menière's disease, using either trans-tympanic or extra-tympanic recording techniques, has become very popular. The presence of an enhanced summating potential (SP) component is considered to be a diagnostic indicator of hydrops. The response evoked by a click stimulus is widely used in this investigation. The aim of this study was to assess the value of tone-pip stimuli for measurement of the SP component in patients with suspected Menière's disease. Extra-tympanic ECochG was recorded from a surface electrode positioned on the postero-inferior quadrant of the ear canal close to the tympanic annulus. Forty patients referred to the Evoked Potentials Clinic at the Queen's Medical Centre were studied. The combined summating potential and action potential waveform (SP/AP) were recorded using click and tone-pip stimuli. The pips had tone frequencies of 1 and 4 kHz and all stimuli were presented with alternating phase at a repetition rate of 10 per second. The percentage SP (%SP), width and latency characteristics of the SP/AP waveform were calculated for each stimulus condition. There were four patients (10%) with an enhanced tone-pip %SP when the click %SP was within normal limits. Width measurement of the tone-pip waveform at the onset point of the response was abnormal in 13 patients (33%) when a similar measurement of the click-evoked response was normal. There were nine of these patients identified by an abnormal width measurement at the 50% amplitude point of the SP/AP waveform. Both tone-pip frequencies were required in order to identify all these abnormal measurements.(ABSTRACT TRUNCATED AT 250 WORDS)