Otosclerosis is a disease of the bone of the otic capsule that causes an abnormal accumulation of new bone, most commonly within the oval window.
Otosclerosis is one of many genetic and acquired conditions that affect the osseous structures. Others include tympanosclerosis, Paget disease, branchio-oto-renal dysplasia, osteogenesis imperfecta, and Goldenhar syndrome.
In otosclerosis, bone is resorbed and redeposited with pathologic consequences. The most commonly affected area involves the stapes; as a result, the stapes becomes immobile and conductive hearing loss develops. Otosclerosis may also cause a sensorineural hearing loss, particularly when the foci of otosclerotic bone are adjacent to the scala media.
Otosclerosis tends to run in families, and half of all cases are inherited. There is a 25% chance of developing otosclerosis if one parent has it and a 50% chance if both parents have it. Otosclerosis is a complex disease with rare autosomal dominant forms caused by a single gene. By linkage analysis, the localization of an otosclerosis gene is chromosome 15q25-q26. Recent studies have shown a more complex genetic picture, implicating multiple other genes (1). The measles virus is hypothesized to play an inciting role in patients with a genetic predisposition for otosclerosis.
Although about 10% of White adults have some otosclerosis (compared with 1% of Black adults), only about 10% of affected people develop conductive hearing loss. Rarely, hearing loss caused by otosclerosis manifests 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, hearing loss is diagnosed. Typically, otosclerosis develops in one ear, although more than half of patients continue developing symptoms in both ears.
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.
General reference
1. Rämö JT, Kiiskinen T, Seist R, et al: Genome-wide screen of otosclerosis in population biobanks: 27 loci and shared associations with skeletal structure. Nat Commun 14 (1):157, 2023. doi: 10.1038/s41467-022-32936-3
