Introduction
Background
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. Women are affected twice as often as are men.
Usually, symptomatic hearing loss from otosclerosis first develops early in the third decade of life, although onset in the teenage years does occur. 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 requires treatment eventually develops in about 1% of the white population. Clinical disease occurs in about 0.5% of Asians and South Americans and in about 0.1% of Africans. The disease is bilateral in most cases.
Pathophysiology
Two separate pathologic phases of the disease process can be identified: an early otospongiotic phase and a 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 Histologic Findings below.
Frequency
United States
Histologically, otosclerosis has a prevalence of about 10%. However, only about 1 in 10 persons with histologic disease are clinically affected, thus placing the prevalence of clinically significant disease at about 1%.
Mortality/Morbidity
The only known 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.
Race
Otosclerosis is much more common in whites than in persons of other races. Histologic otosclerosis occurs in 10-20% of whites but only about 1% of blacks.
Sex
More women seek medical attention for hearing loss due to otosclerosis than do men. 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.
Age
Clinical otosclerosis can manifest as early as age 7-8 years but most commonly appears in persons aged 15-35 years.
Clinical
History
Hearing loss and tinnitus are the principal symptoms of otosclerosis. Hearing loss is progressive but the rate of progression varies and may proceed by fits and starts, even within the same individual. Tinnitus widely varies but generally tends to become more severe as the degree of hearing loss worsens. Occasionally, dizziness can result. The patient may describe only vague disequilibrium or may experience paroxysms of severe rotatory vertigo. Dizziness due to otosclerosis alone is sometimes termed otosclerotic inner ear syndrome. Dizziness secondary to otosclerosis can be difficult to distinguish from other causes, especially secondary endolymphatic hydrops (ie, Ménière syndrome).
- In individuals with a significant history of otitis media, ossicular pathology, especially partial or complete necrosis of the long process of the incus, should be seriously considered. In such circumstances, tympanography may reveal very high compliance (ie, the opposite of otosclerosis). A type AD tympanogram suggests ossicular discontinuity. Often, as incus necrosis proceeds, the union between the incus and the stapes is replaced by a dense fibrous band. Such a fibrous union may result in an air-bone gap that is wider in high frequencies than in low frequencies.
- Congenital stapes fixation is nonprogressive and is detected in the first decade of life. Fixation of the malleal head can occur congenitally, often in association with other stigmata of aural atresia, or it can be acquired, usually due to an infectious process that resulted in tympanosclerosis. Tympanosclerosis can also result in stapes immobility by filling the oval window niche with tympanosclerotic plaques. Such a process usually occurs in individuals with a long history of otitis media and is more commonly unilateral than is otosclerosis.
- Paget disease produces a clinical picture indistinguishable from otosclerosis. Histopathologically, Paget disease begins in the periosteal layer and not within the otic capsule.
- Osteogenesis imperfecta also results in stapes fixation. Osteogenesis imperfecta is readily identified in most individuals who have other stigmata of the disease (eg, multiple flexures, blue sclera) but subtle cases may be indistinguishable from typical otosclerosis. At the time of operation, surgical findings are identical.
Physical
- Tuning fork tests reveal a conductive hearing loss in individuals with footplate fixation. Results of tuning fork tests may be difficult to interpret in patients with mixed losses.
- The Rinne test should demonstrate bone conduction to be better than air conduction (negative Rinne) in patients contemplating a stapes procedure.
- The Weber test should lateralize to the ear with a greater degree of conducting hearing loss.
- The remainder of the physical examination findings should be normal.
- Abnormalities of the tympanic membrane, external ear canal, or middle ear suggest other causes for conductive hearing loss, although they do not rule out the possibility of stapes fixation due to otosclerosis. The exception is the presence of a Schwartze sign. Upon physical examination, this is the finding characteristic of otosclerosis.
More on Otosclerosis |
 Overview: Otosclerosis |
| Differential Diagnoses & Workup: Otosclerosis |
| Treatment & Medication: Otosclerosis |
| Follow-up: Otosclerosis |
| References |
| Next Page » |
References
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Further Reading
Keywords
otosclerosis, hearing loss, conductive hearing loss, sensorineural hearing loss, SNHL, deafness, metabolic bone disease, otic capsule, ossicles, tinnitus, disequilibrium, vertigo, otosclerotic inner ear syndrome, secondary endolymphatic hydrops, Ménière syndrome, otitis media, aural atresia, tympanosclerosis, Paget disease, osteogenesis imperfecta
