What Are the Causes of Otosclerosis?

Otosclerosis is a condition that results from the abnormal growth of the stapes, the last of the tiny bones in the middle ear and the one nearest the entrance to the inner ear. The bone growth causes the stapes to become fixed in the oval window leading to the inner ear, which disturbs the normal passage of sound waves. The result is diminished hearing which can sometimes be severe. Although theories abound, there is no consensus on the root causes of otosclerosis.

Function

Hearing is a complex process. Sound waves travel through the air, are gathered in the outer ear and channeled through the middle ear where they produce a vibration of the ear drum. Three of the smallest bones in the body--the malleus, the incus and the stapes, which are located in the middle ear--transmit the vibrations through the oval window into the fluid-filled cochlea of the inner ear. The cochlea passes the vibrations onto the nerves which pass them on to the brain which then interprets the vibrations as distinguishable information.

Identification

Any abnormal bone growth on the bones of the middle ear, but particularly the stapes, can cause varying degrees of hearing loss. While otosclerosis typically results in conductive hearing loss, in some cases it can also result in damage to the nerve fibers or sensory receptors in the inner ear called senorineural hearing loss.

Risk Factors

According to the National Institute on Deafness and Other Communication Disorders (NIDCD), otosclerosis appears to be a hereditary disease, although the causes are not yet known. Studies indicate a higher risk factor for Caucasian, middle-aged women than other groups. There is also some evidence suggesting a link between viral infections and otosclerosis. Certain hormonal changes due to pregnancy may also contribute to the condition.

Effects

Because otosclerosis appears to be primarily a genetic disorder, research is being done to try to isolate the specific genes involved. At present the NIDCD projects a 25 percent risk of a child with one parent who suffers from otosclerosis to develop the condition. If both parents have otosclerosis the risk factor increases to 50 percent.

Treatment

Approximately 10 percent of American citizens are affected to some degree by otosclerosis. It typically affects both ears and gets progressively worse as the patient ages. Treatment with oral fluoride, calcium or vitamin D are promising, but need more research. Surgery, including new techniques in laser surgery, remains the primary means of curing otosclerosis.

Resources

• National Institutes of Health