A Discussion of Otosclerosis

Dr Nirmal Patel
MBBS (Hons) FRACS (OHNS) MS (UNSW)

Norwest ENT Group (Director of Otology/ Neurotology)
North Shore Skull Base Institute

THE HEARING MECHANISM

In order to understand otosclerosis, one must have some knowledge of the hearing mechanism.

The External Ear
The external ear consists of the auricle and the external ear canal. These structures collect the sound waves and transmit them to the eardrum.

The Middle Ear
The middle ear lies between the eardrum and the inner ear. This chamber contains three bones of hearing: the malleus (hammer), the incus (anvil) and the stapes (stirrup). Vibrations of the eardrum are transmitted across the middle ear space by these three small ear bones. Movement of the third bone (stapes or stirrup) results in fluid waves in the inner ear.

The middle ear chamber is lined by a membrane similar to the lining of the nose and contains secreting glands and blood vessels. This chamber is connected to the back of the nose by a narrow tube called the Eustachian tube.

The Eustachian tube serves to maintain equalisation pressure between the middle ear chamber and the outside atmosphere, as evidenced by the popping sensation noted in the ear during altitude changes.

The Inner Ear
The inner ear is enclosed in dense bone and contains fluids and the tiny hearing cells. The inner ear is lined by a delicate transparent membrane supplied by microscopic blood vessels, in this small chamber fluid waves resulting from movement of the stapes are transformed into electrical impulses in the nerve.

TYPES OF HEARING IMPAIRMENT

The external and middle ear conduct and transform sound; the inner ear receives it. When there is a problem in the external or middle ear, a conductive hearing impairment occurs. When a problem occurs in the inner ear, a sensorineural or nerve hearing impairment is the result. Difficulty in both conduction and sensorineural hearing results in a mixed impairment.

WHAT IS OTOSCLEROSIS?

Otosclerosis is a disease of the inner ear bone, usually involving excessive abnormal bony deposition around the third bone of hearing, the stapes (stirrup) bone, usually causing conductive hearing loss. In some patients the bony deposition extends to the inner ear and a sensorineural or mixed component of hearing loss occurs.
Otosclerosis is a common cause of hearing impairment and is hereditary. The gene that is passed on can often skip generations and therefore the patient may not have any recent family members that have the condition.

Stapedial Otosclerosis

Usually otosclerosis spreads to the stapes (stirrup bone), the final link in the middle ear transformer chain. This stapes rests in a small groove (oval window), in intimate contact with the inner 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 the involvement of the stapes and the degree of nerve impairment present can be determined only by careful hearing tests.

Cochlear Otosclerosis

When otosclerosis spreads to the inner ear a sensorineural hearing impairment may result due to an interference with the nerve function. This nerve impairment is called cochlear otosclerosis, and once it develops it is permanent. In select 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.

TREATMENT OF OTOSCLEROSIS

Medical

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 if there is a component of cochlear otosclerosis.

Surgical

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The stapes operation (stapedectomy) is recommended for patients with otosclerosis who are candidates for surgery. This operation is performed under local or general anesthesia, usually as day surgery. Over 90% of these operations are successful in restoring the hearing permanently.

Stapedectomy is performed through the ear canal under local or general anesthesia. At times an incision may be made behind the ear or in front of the ear canal to remove muscle tissue for use in the operation.

Under high power magnification the eardrum membrane is turned forward and the fixed stapes is partially or completely removed. The stapes may be removed with instruments, a drill, or in some cases, a laser. A wire prosthesis is inserted to replace the diseased stapes bone. The eardrum membrane is then replaced in its normal position.

The wire stapes prosthesis allows sound vibrations to again pass from the eardrum membrane to the inner ear fluids. The hearing improvement obtained is usually permanent.

The patient may return to work in three to four days depending upon occupational requirements. Patients residing outside the local area should plan to remain here overnight. One should not plan to drive a car home from the hospital. Air travel is permissible 48 hours following surgery.

HEARING IMPROVEMENT FOLLOWING STAPES 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 to six months.

The degree of hearing improvement depends on how the ear heals. In the majority of patients the ear heals well 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 1 - 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 1%, complications in the healing process maybe so great that there is 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.

If further loss of hearing occurs in the operated ear, we can offer rehabilitation options including hearing aids, Bone Anchoured Implants or Cochlear (bionic) implants.

TINNITUS

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, this irritation is manifested as ringing, roaring, or buzzing. It is usually worse when the patient is fatigued, nervous, or in a quiet environment. Following the successful stapedectomy, tinnitus is often decreased in proportion to the hearing improvement.

RISKS AND COMPLICATIONS OF STAPEDECTOMY

Dizziness

Since the inner ear is opened for the stapedectomy operation, dizziness is expected for a few days. The dizziness may result in nausea and vomiting. Some unsteadiness is common during the first few postoperative days; dizziness with sudden head motion may persist for several weeks. On rare occasions dizziness is prolonged.

Taste Disturbance and Mouth Dryness

Taste disturbance and mouth dryness is not uncommon for a few weeks following surgery. In 5% of the patients this disturbance may be prolonged.

Loss of Hearing

Further hearing loss develops in 3% of the patients due to some complications in the healing process. In less than 1%, this hearing loss is severe and may prevent the use of an aid in the operated ear.

If further loss of hearing occurs in the operated ear when it is healing, treatment can offered in the form of hearing aids, Bone Anchoured Implants or Cochlear (bionic) implants.

Tinnitus

Should the hearing be worse following stapedectomy, tinnitus (head noises) likewise may be more pronounced.

Eardrum Perforation

A perforation (hole) in the eardrum membrane is an unusual complication. It develops in less than 1% of cases 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.

Infection

Infection after the operation affects 5% of patients and typically resolves spontaneously.

HEARING AIDS

If you are a suitable candidate for surgery, you are also suitable to benefit from a properly fitted hearing aid. If 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”. If deafness is profound then the patient may benefit from a bionic ear (cochlear Implant).

GENERAL COMMENTS

If you are a suitable candidate for surgery and do not have the stapes operation at this time, it is advisable to have careful hearing tests repeated at least once a year.

Should any question arise regarding your hearing impairment, feel free to contact the Norwest Ear, Nose and Throat Group at anytime to further discuss your problem.

Adapted from the Patient Discussion Booklet
Series of the University of Utah Otolaryngology.
Reprinted by Permission.

Reproduction in part or whole of this material is restricted by copyright law unless express written permission is granted by the Norwest ENT Group.

If you would like to discuss the experience of stapedectomy with one of our patients please call:

Cecilia 0432011946 for international callers +614 3201 1946
Ibrahim 0414378508 for international callers +614 1437 8508