Otosclerosis, a disease of the middle ear bones, is a common cause of hearing impairment and is hereditary. Someone in earlier generations of your family had the condition and passed it down to you. Similarly, your descendants may inherit this tendency from you, although the hearing impairment may not manifest itself for a generation or two. Being hereditary, diseases such as scarlet fever, ear infection, measles and influenza have no relationship to the development of otosclerosis.
Function of the ear
The ear is divided into three parts: the external ear, the middle ear and the inner ear. The external ear collects sound, the middle ear mechanism transforms the sound and the inner ear receives and transmits the sound.
Sound vibrations enter the ear canal and cause the eardrum to vibrate. Movements of the eardrum are transmitted across the middle ear to the inner ear fluids by three small ear bones. These middle ear bones (hammer or malleus, anvil or incus and stirrup or stapes) act as a transformer changing sound vibrations in air into fluid waves in the inner ear. The fluid waves stimulate delicate nerve endings in the hearing canals. Electrical impulses are transmitted on the nerve to the brain where they are interpreted as understandable sound.
Types of hearing impairment
The external ear and the middle ear conduct sound; the inner ear receives it. If there is some difficulty in the external or middle ear, a conductive hearing impairment occurs. If the trouble lies in the inner ear, a sensorineural or nerve hearing impairment is the result. When there is difficulty in both the middle and the inner ear a mixed or combined impairment exists. Mixed impairments are common in otosclerosis.
Hearing impairment from otosclerosis
Had we been able to examine your middle ear under the microscope before a hearing impairment developed, we could have seen minute areas of both softening and hardening of the bone. This process may spread to the stapes, the inner ear, or to both sides.
When otosclerosis spreads to the inner ear a sensorineural hearing impairment may result due to interference with the nerve function. This nerve impairment is called cochlear otosclerosis and once it develops it may be permanent. In selected cases medication may be prescribed in an attempt to prevent further nerve impairment.
On occasion the otosclerosis may spread to the balance canals and may cause episodes of unsteadiness.
Usually otosclerosis spreads to the stapes or stirrup bone, he final link in the middle ear transformer chain. This stapes rests in the small groove, the oval window, inn intimate contact with the inter. ear fluids. Anything that interferes with its motion results in a conductive hearing impairment. 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 and the degree of nerve impairment present can be determined only by audiometric examination (hearing tests).
Treatment for otosclerosis
There is no local treatment to the ear itself or any medication that will improve the hearing in persons with otosclerosis.
In some cases medication may be helpful in preventing further loss of hearing.
The stapes operation (stapedectomy) is recommended for patients with otosclerosis who are candidates for surgery. This operations is usually performed under local anesthesia and requires but a short period of hospitalization and convalescence. Over 90 percent of these operations are successful in restoring the hearing permanently.
Stapedectomy or stapedotomy is performed through the ear canal under local anesthesia. At times an incision may be made behind the ear to remove muscle tissue for use in the operation.
With the use of the operating microscope, the eardrum is turned forward. The laser may be used to vaporize parts of the stapes. The remainder of the stapes is removed with an instruments. A small opening is made in the footplate of the stapes with the laser. A stainless steel piston is then placed into this opening and connected to the second bone of hearing, or the incus. The eardrum is hen returned to its normal position.
The wire stapes prosthesis allows sound vibrations to again pass from the eardrum membrane to the inter. ear fluids. The hearing improvement obtained is usually permanent.
Stapes surgery can usually be done on an outpatient basis. Upon occasion the person is admitted overnight and may return to work in seven to ten days depending on the occupational requirements.
One should not plan to drive a car home from the hospital. Air travel is permissible three weeks following surgery. Automobile travel is usually permissible immediately.
The stapes operation can be performed on previously fenestrated ears, providing the hearing nerve function is essentially the same as necessary for an initial stapes operation. Seventy percent (70%) of these operations are successful in improving the hearing.
Hearing improvement after surgery
Hearing improvement may or may not be noticeable at surgery. If the hearing improves at the time of surgery, it usually regresses in a few hours due to swelling in the ear. Improvement in hearing may be apparent within three weeks of surgery. Maximum hearing, however, is obtained in approximately four months.
The degree of hearing improvement depends on how the ear heals. In the majority of patients the ear heals perfectly and hearing improvement is as anticipated. In some the hearing improvement is only partial or temporary. In these cases the ear usually may be reoperated upon with a good chance of success.
In two percent (2%) of the cases the hearing may be further impaired due to the development of scar tissue, infection, blood vessel spasm, irritation of the inner ear or a leak of inner ear fluid (fistula).
In less than one percent, complications in the hearing process may be so great that there is a severe loss of hearing in the operated ear, to the extent that one may not be able to benefit from an aid in that ear. For this reason the poorer hearing ear is usually selected for surgery.
When further loss of hearing occurs in the operated ear, head noise may be more pronounced. Unsteadiness may persist for some time.
Most patients with otosclerosis notice tinnitus (head noise) to some degree. The amount of tinnitus is not necessarily related to the degree or type of hearing impairment.
Tinnitus develops due to irritation of the delicate nerve endings in the inner ear. Since the nerve carries sound, the irritation is manifested as ringing, roaring, or buzzing. It is usually worse when the patient is fatigued, nervous or in a quiet environment.
Following successful stapedectomy, tinnitus is often decreased in proportion to the hearing improvement.
Risks of complications from stapes surgery
Dizziness is normal for a few hours following stapedectomy and may result in nausea and vomiting. Some unsteadiness is common during the first few postoperative days; dizziness on sudden head motion may persist for several weeks. On rare occasions dizziness is prolonged.
Taste Disturbance and Mouth Dryness
Taste disturbance and mouth dryness are not uncommon for a few weeks following surgery. In five percent of the patients this disturbance may be prolonged.
Loss of Hearing
Further hearing loss develops in two percent (2% of the patients due to some complications of the hearing process. In one percent (1%) this hearing loss is severe and may prevent the use of an aid in the operated ear.
Should the hearing be worse following stapedectomy, tinnitus (head noise) likewise may be more pronounced.
A perforation (hole) in the eardrum membrane is an unusual complication. It develops in less than one percent (1%) and usually is due to an infection. Fortunately , should this complication occur, the membrane may heal spontaneously. If healing does not occur surgical repair (myringoplasty) may be required)
Weakness of the Face
A very rare complication of stapedectomy is temporary weakness of the face. This may occur as the result of an abnormality or swelling of the facial nerve.
If you are a suitable candidate for surgery, you are also suitable to benefit from a properly fitted hearing aid. I f you have otosclerosis and are not suitable for stapes surgery, you still may benefit from a properly fitted aid.
Fortunately, patients with otosclerosis very seldom go "totally deaf" but will be able to hear with an electronic aid. The older the patient, the less the tendency for further hearing loss due to the otosclerosis process.