[Clinical electrocochleography in Menière's disease]

Transtympanic electrocochleography (ECochG) was performed on 137 definite Menière ears, 29 normal ears and 383 ears with other diseases. The average SP/AP amplitude ratio (SP/AP) was significantly larger than that of normal subjects in the following four disease groups whose causes are thought to be endolymphatic hydrops: 1) definite Menière's disease, 2) suspected Menière's disease, 3) delayed endolymphatic hydrops and 4) labyrinthine syphilis. The SP amplitude could not provide any information for a differential diagnosis of endolymphatic hydrops from normal subjects nor from other sensorineural deafness . The upper 99% confidence limit of normal SP/AP using a 100dBSPL click was 0.37 for 29 subjects. In patients with Menière's disease the relationship between SP/AP and clinical data such as pure tone threshold, audiogram pattern, results of glycerol test and duration of illness from the first vertiginous attack to the test were investigated. In patients with severe hearing loss, the number of those showing SP/AP of greater than 0.37 was much higher than in patients with less severe hearing loss. There were no relationship, however, between SP/AP and duration of illness, or audiogram pattern, or glycerol test. ECochG was recorded before and after intravenous administration of 50 gr of glycerol (10% solution, 500ml), and a significant decrease of SP/AP was found in 21 Menière ears. However, there were no change of SP/AP after oral administration of 50 gr of glycerol (50% solution, 100ml) and isosorbide (70% solution, 2.0gr/kg of body weight). After endolymphatic sac surgery a decrease of SP/AP of 10% or more was found in 5 ears, an increase of SP/AP in 3 ears, and no change of SP/AP in 3 ears. In the patients showing no change of SP/AP after the surgery, numerical values of vertigo by AAOHNS were higher than in patients showing an increase or a decrease of SP/AP. The results demonstrate the usefulness of ECochG in diagnosis of endolymphatic hydrops and indicate a possibility of monitoring the state of hydrops after administration of glycerol and endolymphatic sac surgery.