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ESSENTIALS OF DIAGNOSIS
Slowly progressive unilateral or bilateral conductive hearing loss.
Most commonly presents by the third and fourth decades.
Frequent family history of otosclerosis.
Normal otoscopic examination or positive Schwartze sign.
Audiogram with Carhart notch and abnormal or absent stapedial reflexes.
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GENERAL CONSIDERATIONS
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Otosclerosis is a disease process unique to the temporal bone and, unlike other generalized bone dyscrasias such as Paget disease and osteogenesis imperfecta, it nearly exclusively involves the otic capsule. Disease progression is characterized by abnormal removal of mature dense otic capsule bone by osteoclasts, and replacement with the woven bone of greater thickness, cellularity, and vascularity. While otosclerosis may potentially involve any part of the bony labyrinth, it carries a distinct predilection for the region near the anterior border of the oval window (fissula ante fenestram). When disease involves the annular ligament of the oval window and stapes footplate, a conductive hearing loss (CHL) invariably occurs. Involvement of other parts of the otic capsule may result in sensorineural hearing loss (SNHL) and vestibular symptoms.
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The true prevalence of histological otosclerosis is unknown. Estimates reported for clinical disease (ie, clinical otosclerosis) range from 0.5% to 1.0%. However, the incidence of subclinical disease (ie, histologic otosclerosis) in unselected autopsy series has been reported as high as 13%. About 15 million people in the United States have been diagnosed with otosclerosis, and it is considered among the most common causes of acquired hearing loss. Compared to its prevalence in Caucasians, otosclerosis is half as prevalent among Asians (0.5%) and one-tenth as common in African-American patients (0.1%). In practice, otosclerosis is seen more often in women than in men by the ratio of approximately 2:1. However, it has been proposed that the incidence may be the same in both sexes and that hormonal influences during pregnancy might cause a more rapid progression in women, bringing them to clinical attention. Symptoms rarely become apparent before the late teenage years, with most patients presenting between the ages of 20 and 45 years.
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Declau
F, Van Spaendonck
M, Timmermans
JP. Prevalence of otosclerosis in an unselected series of temporal bones.
Otol Neurotol. 2001;22(5):596
[PubMed: 11568664]
. (The prevalence of otosclerosis correlated well with the rate of clinically significant disease.)
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Lippy
WH, Berenholz
LP, Burkey
JM. Otosclerosis in the 1960s, 1970s, 1980s, and 1990s.
Laryngoscope. 1999;109(8):1307
[PubMed: 10443838]
. (The audiometric patterns at presentation have changed over the past 37 years.)
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The otic capsule and stapes form from a cartilaginous anlage, which begins endochondral ossification by the 19th week of embryogenesis and is complete by the end of the first year of life. The vestibular surface of the footplate remains cartilaginous throughout life. Bone turnover, which is normally seen in other parts of the body, does not occur in the “healthy” otic capsule ...