Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 96. Cranial Nerve Disorders

Topics: Introduction | Internuclear Ophthalmoplegia | Palsies of Cranial Nerves That Control Eye Movement | Trigeminal Neuralgia | Bell's Palsy | Hemifacial Spasm | Glossopharyngeal Neuralgia | Hypoglossal Nerve Disorders

Bell's Palsy

Bell's palsy is sudden weakness or paralysis of the muscles on one side of the face due to malfunction of cranial nerve VII (facial nerve), which stimulates the facial muscles.

Bell's palsy affects about 23 of 100,000 people at some time. The cause of Bell's palsy is unknown, but it may involve swelling of the facial nerve as a reaction to an immune disorder or a viral infection. Swelling causes the nerve to be compressed and its blood supply to be reduced. Evidence suggests that herpes simplex, a viral infection, is usually the cause. Lyme disease is also a common cause of Bell's palsy, especially in the northeastern United States. In blacks, sarcoidosis is a common cause.

Symptoms

Pain behind the ear may be the first symptom, developing several hours or even a day or two before the facial muscles weaken. In Bell's palsy, facial weakness occurs suddenly and ranges from mild weakness to complete paralysis. The weakness reaches its maximum by 48 hours. Only one side of the face is affected. The weak side 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 a facial expression is made. Most people experience a numbness or heavy feeling in the face, even though sensation remains normal.

When the upper part of the face is affected, closing the eye on the affected side may be difficult and incomplete. Because the eye cannot close completely, it may become dry, resulting in pain, eye damage, and even blindness. The eye also tends to roll upward when it is closed.

Bell's palsy may interfere with the production of saliva, the sensation of taste in the front part of the tongue, or the ability to produce tears. 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 inner 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.

Diagnosis

Bell's palsy can usually be diagnosed based on symptoms. It can be distinguished from a stroke because stroke usually causes sudden weakness only in the lower part of the face rather than the entire face. Also, a stroke typically causes weakness of an arm and a leg.

Doctors can distinguish Bell's palsy from other disorders that are rare causes of facial nerve paralysis because the other disorders usually develop slowly. These disorders include brain tumors, other tumors that compress the facial nerve, infections in the middle ear or mastoid sinuses, and fractures of the bone at the base of the skull. Usually, doctors can exclude these disorders on the basis of the person's history and results of x-rays, computed tomography (CT), or magnetic resonance imaging (MRI). A blood test may be performed to check for Lyme disease or sarcoidosis. There is no specific test for Bell's palsy.

Treatment and Prognosis

Bell's palsy is treated as if the cause were herpes simplex. An antiviral drug called acyclovir is given to prevent the virus from replicating. Corticosteroids, such as prednisone, are given by mouth to reduce swelling of the nerve. For maximum benefit, treatment should start within 2 days of the development of symptoms and be continued for 1 to 2 weeks.

If paralyzed facial muscles prevent the eye from closing completely, the eye must be protected from dryness to reduce the risk of blindness. Eyedrops consisting of artificial tears or a salt (saline) solution are applied to the eye until it can close completely. An eye patch may also be needed.

Mild electrical stimulation of the nerve and massage of the facial muscles have no proven benefit. If no facial movement has returned after 6 to 12 months, an operation--called hypoglossal-facial anastomosis--may be performed to join cranial nerve XII (hypoglossal nerve) to the facial nerve. This operation may partially restore facial movement, but it also causes difficulties in eating and speaking and is therefore rarely performed.

When facial paralysis is partial, most people recover completely within 1 to 2 months whether they are treated or not. When the paralysis is total, the outcome varies. Many people do not recover completely; the facial muscles may remain weak, causing the face to droop.