The relationship of SP and AP findings to hearing level in Menière's disease.

The relationship of summating potential (SP) and action potential (AP) to hearing threshold level was examined in 46 patients with a unilateral Ménière's disease. The SP and AP were recorded with the extratympanic method. The ratio of -SP and AP amplitudes in affected ears to those in contralateral ears (-SP and AP amplitude ratio) at 80 dB nHL of click stimuli was used as parameters of analysis in order to diminish the variability of SP and AP amplitudes among individuals. The results revealed that there is no relationship between -SP amplitude ratio and the hearing threshold level at any frequency, whereas AP amplitude ratio has a significant negative correlation (r = -0.419, p less than 0.01) to the average hearing threshold level at 2-8 kHz, but not at 0.25-1 kHz (p greater than 0.05). The results indicate that an increase in the ratio of -SP amplitude to AP amplitude with the deterioration of the hearing at higher frequencies reported by our previous study (Mori et al., 1987) results from a decrease in AP amplitude rather than an increase in -SP amplitude. The dependence of AP amplitude on hearing threshold level and the independence of -SP amplitude on hearing threshold level suggests that the mechanism underlying the increase in -SP amplitude may be different from that causing the hearing loss in Ménière's disease.