Vestibular symptoms in otosclerosis--correlation of otosclerotic involvement of vestibular apparatus and Scarpa's ganglion cell count.

Although several histopathologic studies have shown otosclerotic involvement of the vestibular apparatus in patients with otosclerosis, the pathogenesis of vestibular symptoms in otosclerosis remains unknown. A quantitative study of Scarpa's ganglion was performed in 217 temporal bones from 118 subjects with otosclerosis. Review of clinical records revealed an incidence of vestibular symptoms in 11.9% of these subjects. Scarpa's ganglion cell counts in temporal bones of subjects with otosclerosis and vestibular symptoms were lower than counts in temporal bones of subjects with otosclerosis but without vestibular symptoms and those of normal subjects. This difference in Scarpa's ganglion cell counts, adjusted for age, between the group with otosclerosis and vestibular symptoms and a group of normal subjects was highly significant (p = 0.0015), whereas the difference in Scarpa's ganglion cell count between a group with otosclerosis but without vestibular symptoms and a group of normal subjects was not significant (p = 0.53). There was also a significant correlation between elevation of the average bone-conduction threshold and the presence of vestibular symptoms in these subjects (p = 0.041). The endosteum of the perilymphatic space of the vestibule and the endosteum of the canal for the superior vestibular nerve or its cribrose area were the two most common sites of involvement by otosclerosis. However, there was no significant correlation between the presence of vestibular symptoms and otosclerotic involvement of any single site or the number of involved sites. Histologic examination of the vestibular nerve fibers and end organs subjacent to otosclerotic foci demonstrated no obvious degenerative changes. Thus our findings appear to suggest that the vestibular symptoms present in patients with otosclerosis are more common in patients with elevated bone conduction thresholds and are correlated with degeneration of the vestibular nerve, which appears to be independent of the severity of otosclerotic involvement of the vestibular end organs.