Otosclerosis (or hardening of the ear) is the most common cause of conductive hearing loss. It causes a slow formation of spongy bone in the otic capsule, particularly at the oval window. This otosclerotic bone growth eventually causes the footplate of the stapes to become locked or fixed in position, disrupting the conduction of vibrations from the tympanic membrane to the cochlea.
Otosclerosis occurs in at least 10% of whites, is twice as common in women as in men, and usually occurs between ages 15 and 50. With surgery, the prognosis is good.
The cause of otosclerosis is not fully understood, although research has shown that otosclerosis tends to run in families and may be hereditary, or passed down from parent to child. People who have a family history of otosclerosis are more likely to develop the disorder. On average, a person who has one parent with otosclerosis has a 25 percent chance of developing the disorder. If both parents have otosclerosis, the risk goes up to 50 percent. Research shows that white, middle-aged women are most at risk.
Some research suggests a relationship between otosclerosis and the hormonal changes associated with pregnancy. While the exact cause remains unknown, there is some evidence associating viral infections (such as measles) and otosclerosis.
Signs and Symptoms
The patient may report a history of slow, progressive hearing loss in one ear, which may have progressed to both ears, without middle ear infection. She may also describe tinnitus and the ability to hear a conversation better in a noisy environment than in a quiet one (paracusis of Willis).
In 20% to 25% of patients, vertigo is experienced, especially after bending over. The patient may also state that she can hear her own voice. This is because the sound is conducted through the bones in the head. Conversation may be inappropriate due to the inability to hear.
Otoscopic examination usually reveals a tympanic membrane that appears normal. Occasionally, you may see a faint pink blush through the membrane from the vascularity of the active otosclerotic bone (Schwartze's sign).
A Rinne test demonstrates that the bone-conducted tone is heard longer than the air-conducted tone. (Normally, the reverse is true.) As otosclerosis progresses, bone conduction also deteriorates. Weber's test is used to detect sound lateralizing to the more damaged ear. Audiometric testing reveals hearing loss, ranging from 60 dB in early stages to total loss as the disease advances.
In most cases, treatment consists of stapedectomy (removal of the stapes) and insertion of a prosthesis to restore partial or total hearing. This procedure is performed on one ear at a time, beginning with the ear that has sustained greater damage. Postoperative treatment includes hospitalization for 2 to 3 days and antibiotics to prevent infection.
Other surgical procedures include fenestration and stapes mobilization; all require normal cochlear function. Postoperative treatment includes hospitalization for 2 to 3 days and antibiotics to prevent infection.
If surgery isn't possible, hearing aids enable the patient to hear conversation in normal surroundings.
Drinking fluoridated water may help prevent otosclerosis in people who are susceptible. There are no other known ways of preventing this condition.
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