Bell's palsy is sudden weakness or paralysis of muscles on one side of the face due to malfunction of the 7th cranial nerve (facial nerve). This nerve moves the facial muscles, stimulates the salivary and tear glands, and enables the front part of the tongue to detect tastes.
Bell's palsy affects about 23 of 100,000 people at some time. Bell's palsy may result from herpes simplex virus type 1, which causes herpes mouth infections. But the cause is sometimes unknown. Lyme disease can cause facial nerve paralysis, which is similar to Bell's palsy. In blacks, sarcoidosis (see Interstitial Lung Diseases: Sarcoidosis) is a common cause of facial nerve paralysis.
Pain behind the ear may be the first symptom. It may develop several hours or even a day or two before the facial muscles weaken. Facial weakness occurs suddenly. The effect ranges from mild weakness to complete paralysis. By 48 hours, the weakness is as severe as it will be. Only one side of the face is affected. It becomes flat and expressionless. However, people often feel as though the face is twisted because the muscles on the unaffected side tend to pull the face to that side every time they make a facial expression. Wrinkling the forehead, blinking, and grimacing may be difficult or impossible. For most people, the face feels numb or heavy, even though sensation remains normal.
Closing the eye on the affected side may be difficult. People may be unable to close the eye completely, and they blink less frequently. The eye also tends to turn upward when it is closed.
Bell's palsy may interfere with the production of saliva and tears. People may have dry eyes and mouth, or they may drool. Because fewer tears are produced and the eye blinks less often (blinking helps moisten the eye's surface), the eye becomes dry, resulting in pain and eye damage. Eye damage is usually minor but can be serious if the eye is not moistened and protected another way. People may be unable to taste with the front part of the tongue on the affected side. The ear on the affected side may perceive sounds as abnormally loud (a condition called hyperacusis) because the muscle that stretches the eardrum is paralyzed. This muscle is located in the middle ear.
Occasionally, as the facial nerve heals, it forms abnormal connections, resulting in unexpected movements of some facial muscles or in watering of the eyes (“crocodile tears”) during salivation. Because the facial muscles are not used for a long time, permanent tightening of the muscles (contractures) occasionally occurs.
There is no specific test for Bell's palsy, but it can usually be diagnosed based on symptoms. Bell's palsy (and other types of facial nerve paralysis) can be distinguished from a stroke because a stroke usually causes weakness only in the lower part of the face rather than in the entire face. People who have had a stroke can close the eyes tightly and wrinkle the brow. Also, a stroke typically causes weakness of an arm and a leg.
Doctors can distinguish Bell's palsy from other, rare disorders that cause facial nerve paralysis (such as tumors, infections, and skull fractures) because the other disorders cause different symptoms and symptoms usually develop slowly. Usually, doctors can exclude these disorders on the basis of the person's history and results of x-rays, magnetic resonance imaging (MRI), or computed tomography (CT). A blood test may be done to check for Lyme disease, and a blood test and a chest x-ray may be done to check for sarcoidosis.
Treatment and Prognosis
An antiviral drug that is effective against herpes simplex virus (such as acyclovir, famciclovir, or valacyclovir) is usually given by mouth even when the cause is unknown. These drugs prevent the virus, if present, from replicating. If symptoms have been present less than 48 hours, a corticosteroid, such as prednisone, is given by mouth to reduce swelling of the nerve. Taking a corticosteroid may slightly speed and improve the recovery of movement.
If the eye cannot close completely, it must be protected from dryness to reduce the risk of eye damage. Eye drops consisting of artificial tears or a salt (saline) solution are applied to the eye until it can close completely. People may need to wear an eye patch some of the time, particularly during sleep. Rarely, in severe cases, the upper and lower eyelids are sewn together.
When facial paralysis is partial, most people recover completely within several months whether they are treated or not. When the paralysis is total, the outcome varies. Tests (nerve conduction studies and electromyography—see Symptoms and Diagnosis of Brain, Spinal Cord, and Nerve Disorders: Electromyography and Nerve Conduction Studies) can be done to help predict the likelihood of recovery. Many people do not recover completely. The facial muscles may remain weak, causing the face to droop.
Last full review/revision July 2007 by Michael Rubin, MDCM