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What Is Otosclerosis?
Otosclerosis is the abnormal growth of bone of the inner
ear. This bone prevents structures within the ear from
working properly and causes hearing loss. For some people
with otosclerosis, the hearing loss may become severe.
How Do We Hear?
Hearing is a series of events in which the ear converts
sound waves into electrical signals and causes nerve
impulses to be sent to the brain where they are interpreted
as sound. The ear has three main parts: the outer, middle,
and inner ear. Sound waves enter through the outer ear
and reach the middle ear, where they cause the eardrum
to vibrate. The vibrations are transmitted through three
tiny bones in the middle ear called the ossicles. These
three bones are named the malleus, incus, and stapes
(and are also known as the hammer, anvil, and stirrup).
The eardrum and ossicles carry the vibrations to the
inner ear. The stirrup transmits the vibrations through
the oval window and into the fluid that fills the inner
ear. The vibrations move through fluid in the snail-shaped
hearing part of the inner ear (cochlea) that contains
the hair cells. The fluid in the cochlea moves the top
of the hair cells, which initiates the changes that
lead to the production of the nerve impulses. These
nerve impulses are carried to the brain, where they
are interpreted as sound. Different sounds stimulate
different parts of the inner ear, allowing the brain
to distinguish among various sounds, for example, different
vowel and consonant sounds.
How Does Otosclerosis
Cause Hearing Impairment?
Otosclerosis can cause different types of hearing loss,
depending on which structure within the ear is affected.
Otosclerosis usually affects the last bone in the chain,
the stapes, which rests in the entrance to the inner
ear (the oval window). The abnormal bone fixates the
stapes in the oval window and interferes with sound
passing waves to the inner ear.
Otosclerosis usually causes a conductive hearing loss,
a hearing loss caused by a problem in the outer or middle
ear. Less frequently, otosclerosis may cause a sensori-neural
hearing loss (damaged sensory cells and/or nerve fibers
of the inner ear), as well as a conductive hearing loss.
What Causes Otosclerosis?
The cause of otosclerosis is not fully understood, although
research has shown that otosclerosis tends to run in
families and may be hereditary, or passed down from
parent to child. People who have a family history of
otosclerosis are more likely to develop the disorder.
On average, a person who has one parent with otosclerosis
has a 25 percent chance of developing the disorder.
If both parents have otosclerosis, the risk goes up
to 50 percent. Research shows that white, middle-aged
women are most at risk.
Some research suggests a relationship between otosclerosis
and the hormonal changes associated with pregnancy.
While the exact cause remains unknown, there is some
evidence associating viral infections (such as measles)
and otosclerosis.
What Are the Symptoms
of Otosclerosis?
Hearing loss is the most frequent symptom of otosclerosis.
The loss may appear very gradually. Many people with
otosclerosis first notice that they cannot hear low-pitched
sounds or that they can no longer hear a whisper.
In addition to hearing loss, some people with otosclerosis
may experience dizziness, balance problems, or tinnitus.
Tinnitus is a sensation of ringing, roaring, buzzing,
or hissing in the ears or head that accompanies many
forms of hearing loss.
How Is Otosclerosis
Diagnosed?
An examination by an otolaryngologist (ear, nose, and
throat physician) or otologist (ear physician) is needed
to rule out other diseases or health problems that may
cause these same symptoms. An audiologist is a hearing
health care professional who is trained to identify,
measure, and rehabilitate hearing impairment and related
disorders. An audiologist uses a variety of tests and
procedures to assess hearing and balance function. The
audiologist may produce an audiogram (a graph that shows
a person's hearing sensitivity) and a tympanogram (a
graph that shows how well the middle ear functions to
conduct sound). Discuss these results with your audiologist/otologist.
How Is Otosclerosis
Treated?
In many cases surgery is an option for treatment of
otosclerosis. In an operation called a stapedectomy,
a surgeon (otolaryngologist or otologist) bypasses the
diseased bone with a prosthetic device that allows sound
waves to be passed to the inner ear. It is important
to discuss the risks and possible complications of this
procedure, as well as the benefits, with the surgeon.
In rare cases, surgery can worsen the hearing loss.
If the hearing loss is mild, surgery may not be an
option. Also, on occasion, some hearing loss persists
after surgery. A properly fitted hearing aid may help
some people with otosclerosis in situations that include
persistent hearing loss. A hearing aid is designed to
compensate for a hearing loss by amplifying sound. An
audiologist can discuss the various types of hearing
aids available and make a recommendation based on the
specific needs of an individual.
What Research Is Being
Done on Otosclerosis?
Scientists are conducting research to improve understanding
of otosclerosis. Genetic studies continue in order to
identify the gene or genes that may lead to this disorder.
Other researchers are studying the effectiveness of
lasers currently used in surgery, of amplification devices,
and of various stapes prostheses. Improved diagnostic
techniques are also being examined and developed.
Where Can I Get Additional
Information?
American
Academy of Audiology
American
Academy of Otolaryngology - Head & Neck Surgery
American
Speech-Language-Hearing Association
Self
Help for Hard of Hearing People Inc. (SHHH)
Source: National Institute on Deafness & Other
Communication Disorders, 2000.
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