Meniere's disease: the selection and assessment of patients for surgery using electrocochleography.

Transtympanic electrocochleography has been used to measure the action potential (AP), summating potential (SP), and cochlear microphonic (CM) in patients with Menière's disease. In this condition the widening of the AP/SP complex is thought to be due to an enhanced negative SP which shows no adaptation and this may be the result of an increased asymmetry produced by endolymphatic hydrops. Measurements have also been made using two groups of agents -- those designed to increase the cochlear blood flow (the metabolic activator naftidrofuryl and inhalations of carbon dioxide) and those designed to reduce the hydrops "osmotically" (glycerol) or by diuresis. It was hoped that the "glycerol dehydration test" when assessed electrocochleographically would lead to a better selection of patients for surgical decompression of the saccus endolymphaticus. It was also hoped that it would lead to a fuller understanding of the electrophysiological changes which occur in Menière's disease. While it appeared that a decrease in the negative SP after glycerol may be a more sensitive indicator of the changes within the cochlea than either pure-tone audiometry or speech discrimination, no clearcut correlations between this change and the surgical result could be demonstrated. In many patients the AP/SP waveform remained unchanged after successful surgery, indicating perhaps that the pathological changes may have been checked but not reversed, while the hearing remained "pegged" at its preoperative level. Electrocochleography during operation failed to show any consistent change in the waveform or CM.