DIAGNOSIS OF ENDOLYMPHATIC HYDROPS WITH L OW-TONE-MASKED OTOACOUSTIC EMISSIONS

A new method of diagnosis of endolymphatic hydrops by recording low-to ne masked evoked otoacoustic emissions (TEOAE) is presented. Methods: A short acoustic stimulus and a masker tone of 30 Hz are applied in an adjustable phase relation simultaneously to the same ear. In the norm al hearing ear the masker shows little influence on the TEOAE at 0 deg rees, whereas the suppression at phase 270 degrees (maximal rarefactio n at the eardrum) is nearly complete. However, in cases of endolymphat ic hydrops this masking effect is reduced or absent, indicating impair ed mobility of the basilar membrane. Results: The masked TEOAE were re corded of patients with normal hearing, Meniere's disease, and sudden hearing loss without vertigo. In Meniere cases with supposed endolymph atic hydrops, the amplitude modulation of the emissions was found to b e much less than in the other groups. Conclusions: Where TEOAE can be recorded, low-tone masking is a quick, objective, and noninvasive meth od for the diagnosis of endolymphatic hydrops.