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As printed in Hearing Health, volume 19:1,
Spring 2003
Contributors: Howard P. House, M.D., Antonio
De la Cruz, M.D., Rick A. Friedman, M.D., Ph.D., and
Fred H. Linthicum, Jr., M.D.
Otosclerosis (oh”-toh-skluh-ROH’ suhs)
(n.) Bony disease involving the middle ear with the
progressive loss of hearing; characterized by the growth
of spongy bone around the stapes and oval window.
Oto means of the ear and sclerosis refers to abnormal
hardening of tissue. While the root words and the description
are easy to understand, the exact nature of otosclerosis
and a potential cure are not yet clear. We do know that
it is a common cause of hearing loss and that it occurs
primarily among adults, more often among women and is
most prevalent among Caucasians.
It is difficult to arrive at an accurate count of
the number of people who actually have the disease.
Some studies show that for the ages between 30 and 50,
from 10 to 18 percent of all white women and 7 to 9
percent of all white men have tissue changes in the
middle ear resulting from otosclerosis. Less than 10
percent of those individuals, however, actually seek
help for hearing loss.
Oriental people have 50 percent fewer cases and it
is very rare among blacks and Native Americans. Frequency
of cases with hearing loss increases in higher age groups
and it is more probable overall for women to experience
impaired hearing from otosclerosis.
Although it is known that there is a hereditary component
in many cases of otosclerosis, it is likely that there
are a variety of genetic contributors. It is also possible
that there are non-genetic causes.
Characteristics
Scientists identified the condition in the 1800s after
recognizing that tissue changes immobilized the stapes,
the smallest bone in the middle ear. Bony growths (otosclerosis
foci) invade the joint of this tiny but important link,
causing conductive hearing loss by interrupting transmission
of sound to the inner ear.
If the abnormal tissue does not interfere with the
bone’s action, a person may have otosclerosis
for years and not know it. The disease sometimes begins
in only one ear but frequently the other ear develops
it too. “Clinical" otosclerosis, when hearing
loss is detectable, may start in the teen years but
is usually noticed in young adults. Rarely does it start
after age 50.
Hearing loss progresses rapidly in some people. In
others it may stay the same for a number of years and
then slowly deteriorate. Many women with otoscleroisis
report that it worsens with pregnancy. This effect may
be due to hormones.
Usually, the maximum amount of hearing loss caused
by the middle ear conductive problems falls in the moderate
range, around 50-60 dB. A sensorineural hearing loss
may also begin, especially in the high frequencies.
One cause for sensorineural loss is cochlear otosclerosis,
which occurs when abnormal bone formations surround
the cochlea. Only a small percentage of people with
the disease develop this type and for this group, onset
is earlier, ranging from the late teens to the early
30s.
It is very rare for otosclerosis to cause sensorineural
hearing loss without conductive loss. The combination
of the two can cause the overall mixed hearing loss
to reach the severe-to profound level.
Standard diagnostic exams for otosclerosis include
the acoustic reflex test that is used to test the motion
of the eardrum and the stapes. This method can detect
otosclerosis in 50 percent of the cases. High resolution
CT scanning is a definitive test.
Genes
Approximately 50 percent of people who have the disease
inherited it. People in the same family who have the
disease usually have similar symptoms; that is, it will
start at roughly the same age and progress at a similar
rate. In contrast, the variation of age at onset and
progression of symptoms when comparing unrelated families
can be quite wide. This suggests that different types
of genes (dominant and/or recessive) may be involved
which makes it very difficult to predict the exact risk
a person may have of developing otosclerosis.
So far three gene locations for otosclerosis have been
mapped. They are in chromosomes 15, 7 and 6. While the
total number of genes involved is not yet known, this
is the first step in identifying the mechanisms and
processes that are responsible for the disease and developing
a way to prevent it.
Treatments
Hearing loss that results from otosclerosis may be corrected
by a surgical procedure to free the stapes, once again
allowing the transmission of sound from the middle ear
into the inner ear. This type of surgery has evolved
over the years because of advances in the techniques,
materials and instruments that are used.
In the 1800s, the first stapes surgeries were performed
without antibiotics or microscopes, resulting in numerous
complications, including meningitis and death. At the
turn of the twentieth century, the American Medical
Association’s International Congress of Otolaryngology
suspended all surgeries for hearing restoration until
complications for the patient could be reduced significantly.
In 1922, Dr. Gunner Holmgren of Stockholm successfully
re-activated the fenestration procedure that had been
used under the earlier primitive conditions. He was
the first to use a microscope to perform the technique
that became the standard treatment for otosclerosis
until the 1950s.
Next came the stapedectomy, a method involving the
removal of the entire stapes bone, sealing the oval
window with tissue and then attaching a prosthesis between
the incus and the oval window membrane. This remained
the most effective method of restoring movement to the
middle ear until the early 1990s.
It was then that medical laser technology entered
the arena. The laser stapedotomy is the most current
procedure for replacing the stapes. It involves making
a 0.7 mm round opening in the fixed footplate of the
stapes with a laser and a diamond burr in order to insert
the prosthesis, a miniature (4 mm – 5 mm) fluoroplast-platinum
or steel piston.
With the laser stapedotomy, there is no mechanical manipulation
of the stapes, reducing complications, and the piston
prosthesis lessens the risk of hearing loss in patients.
The procedure is performed on an outpatient basis, under
local anesthesia and takes less than an hour. Stapedotomy
is a simpler surgery but stapedectomy is still performed
in places around the world with good results.
Whether undergoing a stapedectomy or a stapedotomy,
over 90 percent of patients have their hearing restored.
The majority experience an improvement within three
weeks following the surgery with maximum hearing improvement
obtained in approximately four months.
The degree of hearing improvement depends on how an
individual’s ear heals. For a small number of
patients, hearing improvement may be only partial or
temporary and one to two percent can lose some degree
of hearing.
Hearing aids can often be beneficial. They are a particularly
important alternative when surgery is not recommended
or an individual does not wish to have surgery.
For cochlear otosclerosis, there is no cure but a sodium
fluoride regimen is used in an attempt to retard or
prevent further sensorineural hearing loss. It can take
as long as one year before results become apparent.
Up Ahead
Advances in microsurgical techniques and tools continue
to refine treatments. Genetic mapping studies ongoing
at several centers, including the House Ear Institute,
work to uncover the molecular basis for otosclerosis,
enhancing the possibility of gene therapy as a future
treatment. The prevalence of otosclerosis and its destructive
nature dictate further investigation on this and other
fronts.
Although still beyond our reach, there will be a day
when we are able to offer early identification of individuals
and families who are genetically predisposed to otosclerosis;
when other factors that may contribute to the disease
are pinpointed; and when new interventions, whether
medical, surgical or genetic, will remove the inevitability
of hearing loss for millions of people worldwide.
Contributors to the overview
include:
Howard P. House, M.D., age 94, founder
of the House Ear Institute (HEI) and pioneering ear
specialist who still practices otology at the House
Ear Clinic.
Antonio De la Cruz, M.D., director
of education at HEI and clinical professor of otolaryngology-head
and neck surgery at the University of Southern California.
Rick A. Friedman, M.D., Ph.D., research
section chief of Hereditary Ear Disorders in HEI's department
of cell and molecular biology.
Fred H. Linthicum, Jr., M.D., founder
of HEI's Temporal Bone Bank and a clinical professor
of otolaryngology at the University of Southern California
School of Medicine.
Related article:
Cochlear
Otosclerosis, Our Family Legacy
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