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Written by Dr Robert Mills, consultant ENT specialist

What is Bell's palsy?

Bell's palsy is the sudden onset of weakness of the muscles of one side of the face, for which no other cause can be found.

It is due to a loss of function in the nerve that supplies the facial muscles (the facial nerve). The cause is unknown, but there is some reason to believe that a viral infection of the nerve is responsible.

Bell's palsy is common, affecting approximately 23 per 100,000 people per year, or 1 in 60 to 70 people in a lifetime.

What are the symptoms?

Weakness of one side of the face, the onset of which is usually quite rapid - over a few hours.

Some or all of the following symptoms may also be present on the same side as the weakness:

pain in the ear.
a feeling of numbness of the face, although the sense of touch remains normal.
loss of taste on the front part of the tongue.
loss of saliva production and increase in tear flow.
sometimes, increased hearing sensitivity.

There is no disturbance of balance in Bell's palsy. Because of the weakness or paralysis of the facial muscles the person will usually have difficulty in closing the eye properly on the affected side. The muscles on the unaffected side of the face tend to pull the mouth over to that side, causing the person to drool and often giving the initial visual impression that the abnormal side of the face is the one with the movement.

What can be done to avoid Bell's palsy?

At present we know of nothing that can be done to avoid Bell's palsy.

How does the doctor make a diagnosis?

The diagnosis is made by excluding other possible causes. The ears are examined to exclude evidence of significant ear disease and the mouth to look for evidence of viral infection in the form of blisters. The latter is called Ramsay-Hunt syndrome and is due to infection of the facial nerve with the chickenpox virus, herpes zoster. In this disease the facial weakness is associated with deafness and dizziness.

It may be necessary to test the hearing and occasionally to carry out a scan of the head to exclude other diseases.

What other causes of facial weakness are there?

Skull fractures involving the temporal bone - the bone that contains the middle ear. The facial nerve travels through this bone on its way to the facial muscles and so may be damaged.
Neck injuries, particularly a stab wound to the neck.
Tumours in the upper part of the neck.
Damage to the facial nerve during ear surgery.

Loss of power in one side of the face can be a symptom of a stroke but there will be other features present, such as loss of power in a limb, which point to the correct diagnosis.

Good advice

Head trauma can be minimised by wearing appropriate head protection during sport and when riding a motorbike.

How is it treated?

About 80 per cent of people with Bell's palsy recover spontaneously within three months. Although steroids are still quite commonly prescribed for patients seen soon after the onset of facial power loss, the evidence supporting their use is weak.

The antiviral agent aciclovir (eg Zovirax) has also been used in Bell's palsy but there is insufficient information available to recommend it.

Facial weakness interferes with the ability to close the eyelid normally. 'Artificial tears' (eye drops) may therefore be required to protect the eye.

In long-standing cases, eye closure may be improved by narrowing the space between the eyelids (tarsorrophy) or placing a gold weight in the upper lid.

Plastic surgery techniques can also be used to improve drooping of the lower part of the face in permanent facial weakness.

References
Clinical evidence 2000; 4: 706-709 (BMJ Publishing Group).

Last updated 01.08.2005