Hearing impairment may be caused by otosclerosis, a disease of the inner ear bone. Otosclerosis is a common cause of hearing impairment and is hereditary. Someone in earlier generations of your family had the condition and passed it down to you. Similarly, your descendants may inherit this tendency from you, although the hearing impairment may not manifest itself for a generation or two. Being hereditary, diseases such as scarlet fever, ear infection, measles and influenza have no relationship to the development of otosclerosis.

How does the normal ear funciton?

The ear is divided into three parts: the external ear, the middle ear and the inner ear. The external ear collects sound, the middle ear mechanism transforms the sound and the inner ear receives and transmits the sound. Sound vibrations enter the ear canal and cause the ear drum membrane to vibrate. Movements of the membrane are transmitted across the middle ear to the inner ear fluids by three small ear bones.These middle ear bones (hammer or malleus, anvil or incus and stirrup or stapes) act as a transformer, changing sound vibrations in air into fluid waves in the inner ear. The fluid waves stimulate delicate nerve endings in the hearing canals. Electrical impulses are transmitted on the nerve to the brain where they are interpr-eted as understandable sound.

What are the different types of hearing impairment?

The external ear and the middle ear conduct sound; the inner ear receives it. If there is some difficulty in the external or middle ear, a conductive hearing impairment occurs. If the trouble lies in the inner ear, a sensorineural or nerve hearing impairment is the result. When there is difficulty in both the middle and the inner ear a mixed or combined impairment exists. Mixed impairments are common in otosclerosis.

What are the types of hearing impairment from otosclerosis?

Had we been able to examine your inner ear under a microscope before a hearing impairment developed, we would have seen minute areas of both softening and hardening of the bone. This process may spread to the stapes, the inner ear, or to both these areas.

Cochlear Otosclerosis When otosclerosis spreads to the inner ear a sensori-neural hearing impairment may result due to interference with the nerve function. This nerve impairment is called cochlear otosclerosis and once it develops it is permanent. In selected cases medication may be prescribed in an attempt to prevent further nerve impairment. On occasion the otosclerosis may spread to the balance canals and may cause episodes of unsteadiness.

Stapedial Otosclerosis Usually otosclerosis spreads to the stapes or stirrup bone, the final link in the middle ear transformer chain. The stapes rests in a small groove, the oval window, in intimate contact with the inner car fluids. Anything that interferes with its motion results in a conductive hearing impairment. This type of impairment is called stapedial otosclerosis and is usually correctable by surgery. The amount of hearing loss due to involvement of the stapes and the degree of nerve impairment present can be determined only by careful hearing tests.

What is the treatment of otosclerosis?

Medical There is no local treatment to the ear itself or any medication that will improve the hearing in persons with otosclerosis. In some cases medication may be helpful in preventing further loss of hearing.

Surgical The stapes operation (stapedectomy) is recommended for patients with otosclerosis who are candidates for surgery. This operation is performed under local anesthesia and requires but a short period of hospitalization and convalescence. Over 90 percent of these operations are successful in restoring the hearing permanently.