Otosclerosis
The most common cause of conductive deafness, otosclerosis is the slow formation of spongy bone in the otic capsule, particularly at the oval window. It occurs in at least 10% of the population in the United States. It commonly affects both ears and is seen in many females between the ages of 15 and 30.
Causes
Otosclerosis appears to result from a genetic factor transmitted as an autosomal dominant trait; many patients report family histories of hearing loss (excluding presbycusis). Pregnancy may trigger the onset of this condition.
Signs and symptoms
Spongy bone in the otic capsule immobilizes the footplate of the normally mobile stapes, disrupting the conduction of vibrations from the tympanic membrane to the cochlea. This causes progressive unilateral hearing loss, which may advance to bilateral deafness. Other symptoms include tinnitus and paracusis of Willis (hearing conversation better in a noisy environment than in a quiet one).
Diagnosis
Early diagnosis is based on a Rinne test that shows bone conduction lasting longer than air conduction (normally, the reverse is true). As otosclerosis progresses, bone conduction also deteriorates.
Audiometric testing reveals hearing loss ranging from 60 db, in early stages, to total loss.
Weber’s test detects sound lateralizing to the more affected ear.
Physical examination reveals a normal tympanic membrane.
