Evalution of Vestibular Function in Meniere's Disease

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DESCRIPTION (provided by applicant): Meniere's disease causes considerable morbidity and lost productivity because of its devastating attacks of vertigo and hearing loss. This study aims to characterize how Meniere's disease affects the function of the balance organs of the inner ear and how the human inner ear responds to the increasingly common use of intratympanic gentamicin for the treatment of Meniere's disease. Minimizing the risk of hearing loss with this treatment while achieving vertigo control is the ideal goal. Quantitative testing of the angular and translational vestibulo-ocular reflexes (VOR) in response to high-frequency, high-acceleration stimuli and measures of subjective visual vertical and horizontal provide physiologic measures of the function of the semicircular canals and utricle. These data will be correlated with clinical outcomes in hopes of providing clear guidelines as to how much ablation of vestibular function is necessary to control vertigo in Meniere's disease. In particular, comparisons will be made to data from subjects who underwent surgical destruction of the labyrinth or vestibular nerve in order to determine if complete ablation is necessary or not. Findings from animal models suggest that the key difference between these treatments is that spontaneous vestibular afferent firing is maintained after intratympanic gentamicin but not after surgical vestibular ablation. Differences in the vestibular responses between these treatments may further illuminate the role of spontaneous firing in the vestibular system. Likewise, differences between the eye movements that correct for vestibular reflex deficits after intratympanic gentamicin versus surgical vestibular destruction will be examined to illuminate the role that retained spontaneous firing plays in vestibular compensation and sensorimotor substitution strategies. Long-term follow-up testing in subjects treated with intratympanic gentamicin will show whether or not the lesion is permanent and, if it is not, whether recovery of vestibular function predicts recurrence of vertigo. Comparisons of angular and translational VOR deficits after intratympanic gentamicin should demonstrate whether or not the utricle is less susceptible than the semicircular canals to intratympanic gentamicin.