The summating potential and Meniere's disease. I. Summating potential amplitude in Meniere and non-Meniere ears.

We investigated the relationship between Meniere's disease and the abnormally enlarged summating potential (SP) in a series of patients and normal subjects. Cochlear and auditory nerve responses to rectangular-pulse clicks, delivered at a rate of 8/s and an intensity of 115 dB peak-equivalent sound pressure level, were recorded from ear canal skin. We performed a parabolic regression for SP amplitudes as a function of auditory nerve action potential (AP) amplitudes in normal ears and obtained the 95% confidence interval (+/- 2 SD) for normal scatter around the fitted curve. Sixty-eight percent of SP amplitudes from ears with Meniere's disease exceeded the upper normal confidence limit. In contrast, only 7% of the cochlear ears and none of the retrocochlear ears had SP amplitudes above this normal upper limit. Cochlear microphonic potentials and APs from the ears with Meniere's disease also tended to be larger than normal, but this tendency was not strong enough to be of diagnostic use.