Otosclerosis is a disease of the bone of the otic capsule that causes an abnormal accumulation of new bone within the oval window.
In otosclerosis, the new bone traps and restricts the movement of the stapes, causing conductive hearing loss. Otosclerosis also may cause a sensorineural hearing loss, particularly when the foci of otosclerotic bone are adjacent to the scala media. Half of all cases are inherited. The measles virus plays an inciting role in patients with a genetic predisposition for otosclerosis.
Although about 10% of white adults have some otosclerosis (compared with 1% of African Americans and even less in blacks of primarily African origin), only about 10% of affected people develop conductive hearing loss. Hearing loss caused by otosclerosis rarely may manifest as early as age 7 or 8, but most cases do not become evident until the late adolescent or early adult years, when slowly progressive, asymmetric hearing loss is diagnosed. It is thought that fixation of the stapes may progress during pregnancy.
A hearing aid may improve hearing. Alternatively, stapedectomy to remove some or all of the stapes and to replace it with a prosthesis may be beneficial, but the risks of hearing loss and impaired vestibular function need to be considered.