A non-invasive, objective test of endolymphatic hydrops.

Our previous work has shown that auditory brainstem responses (ABRs) can be used to measure the basilar membrane travelling wave velocity (TWV). Based upon the hypothesis that increased pressure in the scala media will increase the stiffness of the basilar membrane and, hence, increase the speed of the travelling wave. ABRs have been used to provide a means of objectively testing for endolymphatic hydrops. Ten normally hearing subjects and 20 Meniere's patients were tested. The data for the Meniere's group show that the TWV was within normal limits at all frequencies tested, except 5.7 kHz. At this frequency, the TWV greatly exceeded that of the normal group. A short duration (15-30 min) clinical test has been developed which involves the recording of two masked brainstem responses and the measurement of the difference in wave V latencies. Clinical verification that the technique is valid was obtained by monitoring patients undergoing glycerol dehydration. The additional hardware to enable this test to be carried out with a standard evoked response system has been constructed and three, parallel, clinical trials are in hand. Currently, this technique is being applied to longitudinal studies of Meniere's patients and to evaluating the action and efficacy of various drugs. A double-blind trial using a placebo and two different drugs is underway and preliminary results are presented here.