Otosclerosis is a genetically mediated metabolic bone disease that affects only the human otic capsule and ossicles. [1, 2] Its mode of inheritance is autosomal dominant, but penetrance and expressivity both vary.
Usually, symptomatic hearing loss from otosclerosis first develops early in the third decade of life, though onset can occur during childhood. Otosclerosis is well recognized as a cause for conductive hearing loss due to fixation of the stapedial footplate in the oval window niche. Less well recognized is the fact that otosclerosis can involve other portions of the cochlea and produce sensorineural hearing loss (SNHL).
The incidence of cochlear otosclerosis and that of cochlear otosclerosis resulting in clinically significant SNHL are unclear. The disease occurs in 8-10% of the white population; however, of those individuals affected, only 10-15% have clinical symptoms. Consequently, conductive hearing loss that necessitates treatment eventually develops in about 1% of the white population. Clinical disease occurs in about 0.5% of people of Asian and South American descent and in about 0.1% of those of African descent. The disease is bilateral in most cases.
Two separate pathologic phases of the disease process can be identified:
Early otospongiotic phase
Later otosclerotic phase
The otosclerotic phase begins when osteoclasts are slowly replaced by osteoblasts and dense sclerotic bone is deposited in the areas of previous bone resorption. When this process involves the oval window in the area of the footplate, the footplate becomes fixed, resulting in conductive hearing loss.  (See Workup, Histologic Findings.)
Histologically, otosclerosis has a prevalence of about 10%. However, only about 10% of persons with histologic disease are clinically affected, and thus, the prevalence of clinically significant disease is about 1%. The most common morbidity from otosclerosis is hearing loss. Although conductive hearing loss is considered the hallmark of the disease, involvement of portions of the otic capsule other than the stapedial footplate can result in SNHL. Rarely, patients may present with vertigo. 
Clinical otosclerosis can manifest as early as age 7-8 years but most commonly appears in persons aged 15-35 years. Women seek medical attention for hearing loss due to otosclerosis more frequently than men do. However, the disease is not sex-linked, and a histologic study of a large series of temporal bones shows no difference in prevalence between men and women. Otosclerosis is much more common in whites than in persons of other races: Histologic otosclerosis occurs in 10-20% of whites but in only about 1% of people of African descent.
The clinical progression of the disease is unpredictable. Bilateral involvement is typical, and, in most cases, conductive hearing loss progresses until the maximal 50-60 dB loss develops. Sensorineural hearing loss (SNHL) can result in total deafness, but such severe progression is uncommon.
What would you like to print?