Otosclerosis

What is the ear like and how do we hear?

The ear is divided into three parts - the outer (external) ear, middle ear, and the inner ear which includes the cochlea and semicircular canals. The middle ear behind the eardrum is filled with air. Air comes from the back of the nose up a thin channel called the Eustachian tube. In the middle ear there are three tiny bones (ossicles) - the malleus, incus and stapes.

Sound waves come into the outer (external) ear and hit the eardrum. The sound waves cause the eardrum to vibrate. The sound vibrations pass from the eardrum to the middle ear bones. The bones then transmit the vibrations to the cochlea in the inner ear. The cochlea converts the vibrations to sound signals which are sent down the the ear nerve to the brain which we 'hear'.

The semi-circular canals in the inner ear contain a fluid that moves around as we move into different positions. The movement of the fluid is sensed by tiny hairs in the semi-circular canals which send messages to the brain down the ear nerve to help maintain balance and posture.

What happens in otosclerosis?

Otosclerosis is a condition that affects the stapes, one of the tiny bony ossicles in the middle ear. To have normal hearing, the ossicles need to be able to move freely in response to sound waves. What happens is that abnormal bone material grows in and around the stapes. The foot of the stapes, where it attaches to the cochlea, is usually where the condition starts. In time, more and more of the stapes becomes affected. The abnormal bone reduces the movement of the stapes, which reduces the amount of sound that is transferred to the cochlea. The laying down of the abnormal bone is very gradual. However, eventually the stapes becomes 'fixed' which causes severe hearing loss.

In most cases, only the stapes is affected. Sometimes the disease also affects the bony shell of the cochlea. Both ears are usually affected but sometimes only one.

What causes otosclerosis?

The cause of otosclerosis is not known. Bone is continually being broken down and remodelled. It seems that the remodelling process of the stapes becomes faulty. New bone is not made properly and abnormal bone forms. However, the reason this occurs just in the stapes and sometimes the cochlea is not clear.

Hereditary (genetic) factors are important. About 2 in 3 people with otosclerosis have other family members who also have this condition. It is also thought that fluoride possibly has something to do with it. The number of cases in the UK went down after fluoride was routinely added to drinking water. Also, a virus may play a part. It may be that people with otosclerosis inherit a genetic tendency to develop the condition, but it may need a virus infection to 'trigger' the disease process.

Who gets otosclerosis?

Otosclerosis affects about 1 or 2 in 100 people in the UK. It usually first develops between the ages of 15 and 35, but sometimes develops in younger children. Women are affected twice as often as men. Pregnancy is not a cause but may make the condition worse so symptoms are commonly first noticed during pregnancy.

What are the symptoms of otosclerosis?

Hearing loss is the main symptom
The hearing loss may remain mild but commonly it gradually becomes worse. It most commonly affects both ears, but not always. In some people the hearing loss stays mild for a number of years before getting worse. In others the hearing loss quickly becomes worse. Without treatment, in time the affected ears often become totally deaf.

Other symptoms
In addition to hearing loss:

• Tinnitus occurs in about 4 in 5 cases. Tinnitus is an abnormal noise which you hear but it does not come from outside the ear. Noises heard include ringing, whistles, roaring, machine type noises, etc.
• Paracusis is common. This means you tend to hear better when there is a lot of background noise. For example, when talking to someone in a pub or cafe that is full of other people.
• Vertigo (dizziness and balance problems) develops in about 1 in 4 cases. This occurs when the balance mechanism in the cochlea (the semi-circular canals) is affected.

What is the treatment for otosclerosis?

Hearing aids
At first, when the hearing loss is mild, you may not need any treatment. As the disease progresses and hearing loss becomes worse, hearing aids can make a big difference. However, when the hearing loss is severe, hearing aids will not be of much help.

Surgery
An operation can be done to replace the stapes with an artificial plastic bone. In most cases this operation is successful and restores hearing. However, it is a very delicate operation. There is a small risk that the operation will fail and cause total deafness in the operated ear. Also, there is a small risk of damaging other nerves during the operation. The operation may not cure tinnitus, and will not improve hearing in the small number of cases which affect the cochlea.

So, although usually successful, because of the small chance of serious complications, it may be a difficult decision when to opt for an operation. Some people decide to stick with hearing aids until the hearing becomes so bad that the hearing aids are not helping very much. Other people opt for surgery earlier so as not to need hearing aids. When surgery is decided upon, the ear that is most badly affected is operated on first. This is the ear with most to gain if the operation is successful, but the best ear is preserved in the small number of cases where the operation fails.

Fluoride tablets
There is limited evidence that fluoride tablets may possibly slow the progression of the disease in some cases. This is thought to be mainly in the uncommon situation where the cochlea is affected. However, this treatment is not widely used.

Further help and advice

The Royal National Institute for Deaf People (RNID)
RNID Head Office, 19-23 Featherstone Street, London. EC1Y 8SL
Tel: 0808 808 0123  Textphone: 0808 808 9000  Web: www.rnid.org.uk
Provides information and raises awareness of deafness, hearing loss and tinnitus.

© EMIS and PIP 2005   Updated: May 2005   CHIQ Accredited