Cochlear microphonics in Ménière's disease
Ge, N.N.; Shea, J.J.; Orchik, D.J.
American Journal of Otology 18(1): 58-66
1997
ISSN/ISBN: 0192-9763 PMID: 8989953 Document Number: 472285
The pathophysiology of hearing deterioration in Meniere's disease (MD) is unclear. Hair cell loss has been proposed to be the cause of severe hearing loss in Meniere's disease. The cochlear microphonic (CM) is known to be the receptor potential of the outer hair cells in the cochlea. This study measured the CM in Meniere's disease and investigated its relationship with the degree of hearing impairment and endolymphatic hydrops. Transtympanic electrocochleography (ECoG) using rarefaction (RAR) and condensation (CON) tonebursts at 1 kHz was performed on 130 ears of 119 patients. Ninety six ears were diagnosed to have MD and 34 were diagnosed non-Meniere's disease (NMD). The mean amplitude of the CM was 33.10 +- 46.04 mu-V in the MD group and 13.15 +- 12.77 mu-V in the NMD group (p lt 0.001). Enlarged negative summating potential and action potential ratios (SP:AP gt 40%) were found in 81.3% of the MD group and 17.6% of the NMD group. In the MD group, the CM in the group with an enlarged negative SP was 36.98 +- 49.78 mu-V, and 16.31 + 15.88 mu-V in the group without (p lt 0.01). The CM was 34.33 +- 49.28 mu-V in the pure-tone average (PTA) ltoreq 25 dB group, 46.97 +- 58.31 mu-V in the 26-40 dB group, 29.12 +- 42.62 mu-V in the 41-70 dB group, and 26.20 +- 22.41 mu-V in the gt 70 dB group (p gt 0.05). The CMs in 11 pairs of MD ears and sensorineural hearing loss (SNHL) ears with matching hearing (MD 44 dB, SNHL 45 dB) were measured. They were 71.42 +- 75.94 mu-V and 7.90 +- 5.89 mu-V, respectively (p lt 0.01). Our study shows that the CM is higher in ears with endolymphatic hydrops, evidenced by an enlarged SP:AP ratio, than ears without and the CM shows no statistical difference in groups with different levels of hearing loss. These findings suggest that hearing loss with a large CM in Meniere's disease patients may be the result of an alteration of cochlear mechanics and only severe hearing loss with a small CM is caused by hair cell loss. The CM measurement, to evaluate the hair cell status, may be helpful in identifying patients whose hearing may be recoverable if the underlying hydrops can be corrected. Our data do not permit the conclusion that an enlarged CM can be used in the diagnosis of MD.