Foci of otosclerosis, which may be found anywhere in the temporal bone, gradually expand and coalesce. Fixation of the stapes occurs when the otosclerotic lesion involves the stapes footplate or its annular ligament, leading to conductive hearing loss. The lesion may spread to involve the cochlea and cause a sensorineural hearing loss. What instigates this osseous change and its mechanism is unknown. Epidemiology Females are affected twice as often as males.
Inheritance is autosomal dominant.
No association has been found with chromosome markers or with ABO or HLA antigens. The remaining cases occur sporadically, with autosomal recessive inheritance, spontaneous mutation, and nongenetic causes offered as putative mechanisms. Otosclerosis is rarely seen in patients under 5 years and it most often occurs between ages 30 and 49. Typically, patients present with a history of gradually progressive hearing loss that is usually bilateral and often asymmetric. The frequency of vestibular symptoms may vary, but can include vertigo, postural imbalance and unsteadiness when walking in the dark or with eyes closed.