Article updated and reviewed by Peter B. Kang, MD, Assistant in Neurology, Children's Hospital Boston, and Instructor in Neurology, Harvard Medical School, Boston, MA on April 18, 2005.
Bell's palsy is a facial paralysis caused by an irritation of cranial nerve VII (seven) with no apparent cause. This excludes facial paralysis associated with known causes such as infection or stroke. Cranial nerve VII controls most facial muscles, including those needed to smile, blink, and wrinkle the forehead. The nerve also controls the function of certain salivary glands and the lacrimal (tear) glands as well as the tiny muscles inside the ear that dampen loud noises.
Bell's palsy, named after the 19th-century Scottish surgeon Sir Charles Bell, afflicts about 20,000 Americans each year. The nerve becomes inflamed and swollen within a bony tunnel in the skull that opens just beneath the ear.
The cause of the nerve irritation associated with Bell’s palsy is unknown. Anecdotally, exposure to cold is a frequently cited cause – for example, driving with a car window open in frigid weather, or sleeping with the window open on a chilly night. This association remains speculative. Some evidence suggests that the cause is inflammation of cranial nerve VII triggered by a viral infection, perhaps in the herpes family. The risk increases through the first 30 years of life, remains steady until approximately 70 years, then increases further. People with diabetes or high blood pressure, as well as pregnant women, are at slightly greater risk, but most patients are ordinary people with no known predisposing factors. Some cases have recently been reported after administration of intranasal influenza vaccine.
The classic presentation of Bell's palsy is weakness on one side of the face. The potential range of weakness is wide – it may range from difficulty blinking all the way to a complete paralysis on one side of the face with an inability to close the eye. Onset usually occurs acutely, but the weakness may worsen for 24 to 48 hours before stabilizing.
The first awareness of the problem may involve drooling after brushing the teeth or when drinking, an asymmetrical appearance of the mouth noticed in the mirror, an inability to whistle, or excessive tearing in one eye. A man may say that he was unable to blow out his cheeks when shaving. Sometimes the onset is subtle and a family member or a work associate is the first to notice the patient's facial asymmetry.
People with Bell's palsy may describe the sensation of unilateral loss of facial movement as deadness, loss of feeling, or numbness, although the affected part of the face is neither asleep nor tingling. Misidentification of the affected part is common. Alteration of taste or hearing is occasionally a symptom.
It is important to remember that facial paralysis does not always mean an individual has Bell’s palsy. Other diagnoses should be considered, especially stroke, Lyme disease, and varicella zoster (Ramsey Hunt syndrome). Less common causes include HIV infection, sarcoidosis, Sjögren’s syndrome, amyloidosis, and tumors. Only a physician can distinguish among these possibilities by performing a careful examination. Diagnostic studies such as Lyme titers and neuroimaging may be indicated depending on the individual case.
A primary concern in the management of Bell's palsy is eye care. The inability to close one eye may lead to corneal abrasions and other injuries, especially during sleep. Regardless of what other therapy is undertaken, dark glasses should be worn during the day, eye drops used to prevent drying and a bland eye ointment applied before retiring to bed for the night.
An oral steroid such as prednisone is commonly prescribed. The scientific basis for this treatment is that is helps reduce the inflammation of the nerve and shorten the recovery period. Several studies suggest that prednisone is effective in shortening the disease course and improving recovery rates, but other studies show little benefit. An improved rate of recovery with steroid therapy was especially noticeable in a group of patients with diabetes.
The use of antiviral medications such as acyclovir, often in addition to prednisone, is somewhat controversial. It is clearly justified when there is evidence of facial palsy caused by varicella zoster infection (Ramsey Hunt syndrome), but there is less evidence to support its use in cases of Bell’s palsy, where the evidence for a viral cause is less convincing to date.
In severe cases, surgery can relieve pressure on the nerve at the narrowest point of the bony canal and potentially avoid permanent nerve damage, but this procedure remains controversial. After approximately the first two weeks, permanent nerve damage has probably already occurred, and surgery is much less likely to be beneficial. Thus, the optimal time for surgery to be considered is during the second week of the illness, if there is no sign of improvement. Permanent hearing loss may occur as a complication of the surgery.
The vast majority of individuals with Bell’s palsy recover completely or have minimal deficits, even without treatment. The percentage appears to be somewhat higher with medical and surgical treatment. In the small number of patients who have significant permanent deficits, reconstructive surgery may sometimes be beneficial.
Editorial review provided by VeriMed Healthcare Network.