Photo by Mark Thomas Acosta
What is otosclerosis?
Otosclerosis is defined as abnormal bone growth in the ear, eventually resulting in hearing loss. It can be an inherited disorder, resulting in abnormal hardening of bone in the middle ear and sometimes inner ear. In the middle ear, otosclerosis prevents the stapes, one of the bones in the middle ear, from vibrating correctly in response to sound waves. In the inner ear, cochlear otosclerosis causes reduced function of the hearing cells within the cochlear.
Over time both physiological and anatomical changes occur, slowly leading to hearing loss. Otosclerosis is the most frequent cause of middle ear hearing loss in young adults, affecting about 10% of the population of the United States. Otosclerosis usually affects both ears, and is most commonly seen in women and girls ages 15 to 30 years old. Risks factors include pregnancy, which may trigger its onset, and a family history of hearing loss and otosclerosis.
Usually otosclerosis involves the stapes, or stirrup-shaped, bone. The stapes bone is positioned in a small groove called the oval window and is in intimate contact with the inner ear fluids. 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.
The amount of hearing loss due to involvement of the stapes (stapedial otosclerosis), and the degree of hair cell loss (cochlear otosclerosis) present can be determined only by a careful hearing test.
When otosclerosis spreads to the inner ear, a sensorineural hearing impairment (hair cell loss) may result due to interference with the inner ear function. This hearing impairment is called cochlear otosclerosis, and is permanent once it develops. This otosclerosis disease process affects the cochlea because the disease causes the release of enzymes which are toxic to the hair cells and leads to cochlear deterioration. In addition, there are some other connective tissue changes which result in bone destruction. This process, however, is limited to the ear and involves no other organs. When one has otosclerosis, it may affect only the stapes, the inner ear, or both areas. In selected cases, medication may be prescribed in an attempt to prevent further hair cell loss and subsequently prevent further inner ear damage. This medication is sodium fluoride. On occasion the otosclerosis may spread to the balance canals and may cause episodes of unsteadiness or dizziness.
Signs and Symptoms
Progressive conductive hearing loss is the most typical symptom of the stapedial types of otosclerosis. In pure cochlear otosclerosis, a sensorineural hearing loss is the main finding. The 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.
A complete examination of the ears may rule out other causes of hearing loss. Audiometry will determine the extent of hearing loss. Balance testing will help evaluate functions of the inner ear if necessary. Additionally, a head CT scan may be used to distinguish otosclerosis from other causes of hearing loss.
Otosclerosis may be slowly progressive, and the condition may not require treatment until the extent of hearing loss is significant. Medications such as sodium fluoride can be used, not to return hearing loss but to slow or prevent the loss of further hearing. This medication is given to those patients who have evidence of having hair cell loss, as a result of involvement of the cochlea. Other homeopathic treatments involve the use of calcium or vitamin D, which may help to stabilize the hearing loss. However, their benefits have not been proven. Externally worn hearing aids represent a non-surgical option for treatment.
The laser stapedotomy operation is recommended for patients with otosclerosis who are candidates for surgery. This operation is performed under local or general anesthesia as an outpatient surgery, and recovery is usually quick. Over 90 percent of these operations are successful in restoring hearing permanently.
For the stapes operation to be successful in restoring hearing in otosclerosis, the hearing nerve must be able to receive and transmit sound to the brain. Careful and thorough hearing tests are necessary to determine the hearing nerve function.
For more information about the surgical treatment of otosclerosis, please click the following link: Surgical Treatment for Otosclerosis.