Otosclerosis is an
abnormal microscopic growth and repair of bone in the walls of the inner ear.
Frequently this causes the stapes bone to become frozen in place or fixed.
Normally the stapes, the smallest bone in the body, vibrates freely to allow the
transmission of sound into the inner ear. When it becomes cemented to the
surrounding bone by the disease, it prevents sound waves from reaching the inner
fluids, and hearing is impaired. The disease is a little mysterious. It is a
disease that runs in families. While it is thought to have a genetic basis, no
gene defect has been identified yet. Studies in Scandinavia have suggested that
fluoridation of the water may reduce the development of this disease. As a
result of these studies, some doctors recommend that their patients take
fluoride pills to slow progression in those patients who have the disease.
Fluoride containing pills are an over the counter medication in the US. Another
theory is that early exposure to measles might cause the disease to progress or
develop. There is little doubt that the disease is more common in women of
childbearing age than it is in men. Pregnancy seems to cause the disease to
progress. Women who have the disease may experience increased hearing loss with
each pregnancy. The disease usually begins in the teens or early 20's.
Otosclerosis affects the ears alone and does not involve other parts of the
body. When this condition is present, both ears are usually involved but
frequently it is not symmetric.
Normally, sound is funneled by the auricle or outer ear
through the ear canal to the eardrum. Movement of the eardrum is then
transferred via a chain of bones. These three small bones end with the stapes
bone moving in and out of the oval window in the inner ear. The movement of the
stapes sets up a wave motion in the fluids of the inner ear. This in turn
stimulates small hair cells in the inner ear that signal the nerve of hearing.
The nerve then carries the sound information to the brain.
Occasionally the otosclerotic bone involves other
structures so that the inner ear itself is damaged. But otosclerosis can also
involve the other bones of hearing so that they cannot move properly. If the
inner ear is involved, the hearing loss may be more than a conductive hearing
loss. This means that a mixed loss of both conductive and sensorineural loss
exists in these individuals. Surgery will only correct the conductive component
of the hearing loss. The sensorineural hearing loss cannot be surgically
corrected.
How is it treated?
There is no known medication available for treating
otosclerosis. Some individuals have recommended the use of fluoride to prevent
extension of the disease into the inner ear. Most individuals obtain fluoride
through their drinking water. Those individuals who consume filtered or bottled
water may consider the use of additional fluoride in their diet or as a dietary
supplement. Most patients can wear a hearing aid successfully, but it is only
helpful when worn. If a patient takes off the hearing aid at night, they may be
unable to hear important sounds like children, alarms, or telephones. Stapes
surgery can correct the conductive component of the hearing loss.
Stapes surgery is done using an operating microscope.
The surgeon usually performs the operation under general anesthesia. Some
individuals will tolerate local anesthesia and can have the procedure done using
a technique called twilight sleep. The ear canal is anesthetized while the
patient is sedated. Some surgeons prefer the use of general anesthesia. The
surgeon will fold the eardrum forward looking into the middle ear space. A laser
is usually used to remove a segment of the stapes and a metal prosthesis is
inserted into an opening in the inner ear. The prosthesis is usually crimped
into position on to the incus bone.
Individuals who have successful surgery sometimes awake
and immediately notice improvement in hearing. Most individuals however will
wait 2 months before blood and fluid is clear from the middle ear and packing is
removed from the ear canal. Final results of surgery can take several months to
fully develop.
Risks
No operation is foolproof.
While stapes surgery is usually short, taking less than one hour to complete, it
has some risks. There is a risk that there will be greater hearing loss. There
are other risks such as vertigo, taste changes, facial weakness, tinnitus and
infection. While complications are infrequent, they still occur. In addition to
the risks of the operation itself there are risks from having a foreign material
in the body.
Conclusion
The chances of obtaining a
good result from this operation are quite high. A small number of patients may
not obtain ideal results. The risks of this operation are the same as any other
operation of the ear.