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Otosclerosis
Middle ear stapedial otosclerosis
How is otosclerosis diagnosed?
Otosclerosis is defined as an abnormal bone growth in the ear, affecting the stapes bone, which eventually results in a hearing loss. This hardening of bone can occur in the middle ear, the inner ear, or both parts of the ear. Otosclerosis can cause different types of hearing loss, depending on which structure within the ear is affected. When this bone growth involves only the stapes (middle ear bone) it is called stapedial otosclerosis and causes only a conductive hearing loss. When the bone growth spreads to the inner ear (cochlea) it is referred to as cochlear otosclerosis and results in a sensorineural hearing loss. When both portions of the ear are involved, a mixed hearing loss (conductive and sensorineural) occurs. The amount of hearing loss present due to involvement of the stapes (stapedial otosclerosis) and the degree of hair cell loss (cochlear otosclerosis) can be determined only by a careful hearing test.
Facts about otosclerosis
- Otosclerosis is typically inherited with an autosomal dominant transmission (meaning there is a 50% chance of being inherited), although it has variable penetrance ( meaning there can be “skipped generations”).
- It is the most frequent cause of middle ear hearing loss in young adults, affecting about 10% of the population of the United States.
- It usually affects both ears, but can be unilateral.
- The onset of the hearing loss and related symptoms usually arise between 15 and 45 years in 90 percent of cases.
- It can occur equally in men and women, but there are more women affected with the disease because of a higher female to male ratio.
- Otosclerosis is a progressive disease with an unpredictable course.
- It is often noticed following the first pregnancy and appears to have some homonal relationship.
- Otosclerosis commonly affects Caucasians and Asians; it is less frequently in persons of African descent.
- Because the hearing loss develops slowly, patients are often unaware of its initial onset. They may experience tinnitus long before they recognize the lessened hearing ability. Tinnitus is present in a majority of otosclerotic patients.
- In addition to the hearing loss, some people with otosclerosis may experience dizziness or balance problems.
Middle ear stapedial otosclerosis
Otosclerosis usually involves the stapes or stirrup-shaped bone. The stapes bone is positioned in a small groove called the oval window and is in contact with the inner ear fluids. Under normal conditions, the stapes moves in and out of the opening in the inner ear, at the oval window. There is a special joint around the stapes and cochlea, which allows movement of the stapes. Beneath the stapes is perilymph fluid, which moves in waves when the stapes is moving. Otosclerosis prevents the stapes, the smallest bone in the middle ear, from vibrating correctly because the moveable joint is replaced with the abnormal bone growth. This causes fixation or immobility of the stapes in the oval window. As the stapes
becomes immobile, it cannot transmit the sound passing waves to the inner ear. As a result of the inability of the stapes bone to vibrate the inner ear fluid, a conductive hearing impairment occurs. This type of impairment is called stapedial otosclerosis and is usually correctable by surgery.
Cochlear otosclerosis
When otosclerosis spreads to the inner ear, a sensorineural hearing 
impairment (hair cell loss) results due to interference with the inner ear function. This hearing impairment is called cochlear otosclerosis, and once it develops, it is permanent. Bone resorbing cells called osteoclasts in the ear cause a release of enzymes (substances like cytokines and trypsin), which damage inner ear hair cells. This process, however, is limited to the ear and involves no other organs.
Otosclerosis symptoms & signs
A progressive hearing loss is the most typical symptom of otosclerosis. The type of hearing loss, either conductive (stapedial otosclerosis) or sensorineural (cochlear otosclerosis) can only be determined by evaluating the hearing. Hearing loss appears to be accelerated by pregnancy. In addition to a hearing loss, some patients experience dizziness or unsteadiness. It is usually like disequilibrium and not true spinning vertigo. Often the dizziness or disequilibrium disappears after a stapes operation. Most patients with otosclerosis notice tinnitus (ear noise) to some degree. Tinnitus develops due to changes in the hearing pathway. It is usually more apparent when the patient is fatigued, nervous, or in a quiet environment. The amount of tinnitus is not necessarily related to the degree of hearing impairment. Following successful stapes surgery, the tinnitus is often decreased or eliminated.
How is Otosclerosis Diagnosed?
Otosclerosis diagnosis & tests
A complete examination of the ears may rule out other causes of hearing loss. Audiometry will determine the extent and type of hearing loss. Initially the loss is seen in the low frequencies (with stapedial otosclerosis) and as the disease progresses all frequencies are involved. The conductive loss continues to worsen as the footplate of the stapes becomes more fixed. The stapedial reflex is lost and the tympanogram is typically shallower (e.g. Type As). When cochlear otosclerosis is present, a loss of bone conduction will be seen. The decline in bone conduction will be progressive as more hair cell loss occurs. With the loss of bone conduction, word understanding will decline.
Balance testing will help evaluate functions of the inner ear if necessary. Additionally, a CT scan of the temporal bones (e.g. the inner ear structures) may be used to distinguish cochlear otosclerosis from other causes of hearing loss. Specifically there will be areas of less dense bone in the otic capsule around the cochlea (e.g. luciencies - like the holes seen in Swiss cheese).
Otosclerosis Treatment
Medicinal
Otosclerosis may be slowly progressive, not requiring treatment until the extent of the hearing loss is significant. There is no medical treatment for the conductive hearing loss. Medication such as sodium fluoride can be used when the inner ear type (e.g. cochlear otosclerosis) is involved, not to return the sensorineural hearing loss back to normal, but to slow or prevent further hair cell loss. This medication is only given to those patients who have evidence of having hair cell loss, as a result of involvement of the cochlea. Sodium fluoride is a substance that appears to increase the hardening of the bone around the cochlea and inhibit osteoclast activity. In addition some antioxidants may play a role in decreasing the osteoclast activity, providing some benefit. Common antioxidants are Bioflavanoids (often referred to as the P vitamins). There are 4 forms including Proanthocyanidins, Quercetin (most active of the flavonoids), Citrus bioflavanoids, and Green Tea Polyphenols.
Amplification
Hearing aids represent a non-surgical option for treatment when the hearing loss is significant. Hearing aids are effective for both the stapedial otosclerosis and/or cochlear otosclerosis conditions.
Surgical
In the majority of cases, surgery is an option for treatment of otosclerosis. Use of a prosthesis or laser can provide improved movement of the stapes bone. A stapedectomy involves the entire removal of the stapes and its replacement with a prosthesis. Another option is a small fenestra stapedotomy, where only a portion of the stapes bone is removed and a small opening in made in the bottom (footplate) of the stapes bone allowing a small prosthesis to move the fluid in the inner ear. A third option is the laser stapedotomy operation, which makes an opening in the bone to allow for fluid movement, and is more often recommended for patients with stapedial otosclerosis, who are candidates for surgery. This operation is performed under local or general anesthesia as an outpatient surgery. Recovery is usually quick and hearing is permanently restored in over 90 percent of these operations. For the stapes operation to be successful in restoring hearing in otosclerosis, the bone conduction (e.g. a function of hair cell function) must be able to receive and transmit sound to the brain adequately. Therefore, the degree of sensorineural hearing loss will be important in determining the expected results of the surgery. It is important to discuss the risks and possible complications of the procedure, as well as the expected benefits. In the majority of cases the hearing is improved. In rare cases, surgery can worsen the hearing loss.
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