Otosclerosis

What is the ear like and how do we hear?

The ear is divided into three parts - the outer (external) ear, the middle ear, and the inner ear. 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 (also known as the hammer, anvil and stirrup). The inner ear includes the cochlea and semicircular canals.

What happens in otosclerosis?

Otosclerosis is a condition that mainly 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 in otosclerosis 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 can cause severe hearing loss. The hearing loss is known as conductive hearing loss.

In most cases, only the stapes is affected. Sometimes the disease also affects the bony shell of the cochlea and the nerve cells within it. If this is the case, the damage to the nerve cells means that the transmission of nerve impulses to the brain can be affected. A different type of hearing loss, called sensorineural hearing loss, can occur.

Both ears are usually affected in otosclerosis but sometimes only one.

What causes otosclerosis?

The exact cause of otosclerosis is not known. Normally, bone is continually being broken down and remodelled. In otosclerosis, 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 entirely clear.

Hereditary (genetic) factors seem to be important and the tendency for otosclerosis can be inherited. About 2 in 3 people with otosclerosis have other family members who also have this condition. However, some people with otosclerosis have no family history. Also, a virus may play a part, and the measles virus has been suggested. The number of people diagnosed with otosclerosis seems to have decreased since the measles virus vaccination has been given. 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.

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. However, the possible link with low levels of fluoride is controversial.

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 usually 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. Tinnitus tends to worsen as hearing loss worsens.
• 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.

How is otosclerosis diagnosed?

In otosclerosis, your ear drum usually looks normal when your doctor looks inside your ear using an auriscope (the common instrument used to look inside your ears if you have earache). Generally, you will need to be seen by an ear, nose and throat specialist to diagnose otosclerosis. Hearing tests will show a specific pattern of hearing loss in otosclerosis. CT scanning may also sometimes be used.

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 may not be of much help.

Surgery

The most common operation that is done is to replace the stapes with an artificial bone made of plastic or metal. The operation is called a stapedectomy. In most cases this operation is successful and restores hearing. It may also reduce the chance of otosclerosis progressing to affect the inner ear. 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 and of causing disturbance to balance or taste. The operation may not cure tinnitus, and will not improve hearing in the small number of cases which affect the cochlea. You should ask your surgeon about their success rates for this type of surgery.

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 it means that the best ear is still 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.

Hormone tablets and the contraceptive pill

Some doctors feel that taking the contraceptive pill or hormone replacement therapy may make otosclerosis worse. However, others disagree with this. If you have otosclerosis and are considering taking hormone treatment such as this, you should discuss the pros and cons fully with your doctor.

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.

British Tinnitus Association

Ground Floor Unit 5, Acorn Business Park, Woodseats Close, Sheffield. S8 0TB
Tel: 0800 018 0527 Minicom: 0114 258 5694 Web: www.tinnitus.org.uk
Provides support and advice about tinnitus, including advice about otosclerosis.