Summating potentials in Menière's disease.

The summating potentials in response to tonebursts of 2, 4, and 8 kHz were studied in a group of 112 patients diagnosed as having Menière's disease, and the results were compared with recordings from 27 normal human ears. Subdivision of the Menière ears into a low-threshold (threshold less than 50 dB HL) and a high-threshold group (greater than 50 dB HL) proved to be functional in relation to the behaviour of the SP. The data of the low-threshold Menière group did not differ significantly from the normal data, whereas the high-threshold Menière group showed significantly smaller summating potentials. Up to hearing thresholds of 50 dB, the detection threshold for the SP was independent of the hearing threshold; at higher hearing losses, the increase in SP threshold equalled the increase in hearing loss. Analysis showed that the correlation found between the changes in SP and hearing threshold in individual patients did not differ significantly from zero for threshold values below 50 dB. The overall conclusion is that in Menière ears hearing losses up to about 50 dB are not related to changes in the hair cells, since the SP does not change, whereas the increase in the amount of hearing loss above 50 dB HL is paralleled by a loss in sensitivity of the summating potential and is therefore related to a functional loss of hair cells.