Otosclerosis literally means "ear hardening." This condition affects the tiny bones of the middle ear called the ossicles, causing them to grow abnormally. The abnormal new bone growth can interfere with the conduction and perception of sound, causing gradual hearing loss. In some cases, the hearing loss can become severe and debilitating.
Physiology
In a normal ear, sound waves cause the eardrum to vibrate and the ossicles amplify the vibrations. The deepest bone of the middle ear, the stirrup or stapes, beats against the oval window, the entrance to the inner ear, rocking the fluid in the cochlea. The motion triggers the hair cells in the cochlea to generate nerve impulses that the brain finally interprets as sound. With otosclerosis, abnormal new growth of the stapes can freeze it in place, stopping the chain of events in hearing.
Types
Otosclerosis can cause hearing loss through two different mechanisms. Usually, conductive hearing loss occurs. The bones of the inner ear, fused in place by the abnormal new bone growth, cannot vibrate correctly to conduct the sound impulse on to the inner ear. In some cases, sensorineural hearing loss occurs as well. New bone growth near to the bony canal of the cochlea can damage its delicate hair cells, disrupting the transformation of vibrations into electrical nerve impulses.
Frequency
According to the National Institute on Deafness and Other Communication Disorders, or NIDCD, white middle-aged women have the highest risk for otosclerosis. NIDCD also cites a genetic contribution to otosclerosis: People with one affected parent have a 25 percent chance of developing otosclerosis and the risk increases to 50 percent if both parents have it.
Otosclerosis is more common in whites than blacks. The Merck Manual says that about 10 percent of white adults have some degree of otosclerosis, as compared to only 1 percent of black adults. Of all people affected with otosclerosis, only 10 percent develop hearing loss.
Symptoms
The Merck Manual says that hearing loss with otosclerosis can manifest as early as age 8, although more commonly symptoms begin in late adolescence or early adulthood. Most patients lose their hearing gradually and the NIDCD says that perception of deep, low frequency sounds or low volume sounds such as whispering usually occurs first. Other symptoms such as dizziness or tinnitus—a ringing, buzzing or roaring in the ears—might occur too.
Treatment
In cases of conductive hearing loss with normal sensorineural function, hearing aids or surgery can restore hearing. Hearing aids help by amplifying the sound to override the function of the faulty stapes. In the microsurgical procedure called stapedectomy, the surgeon removes the stapes and inserts a prosthetic device to replace its function.
