The most common cause of facial weakness, which occurs suddenly, is referred to as "Bell's palsy". It is a form of facial paralysis resulting from damage to the seventh cranial (facial) nerve and is probably due to the body's response to a virus.
In reaction to the virus, the facial nerve within the ear (temporal) bone swells and puts pressure on the nerve in the bony canal. This damages the nerve by compression and is thus not a disease of the nerve itself.
In addition to one-sided facial paralysis with possible inability to close the eye, symptoms of Bell's palsy may include pain, tearing, drooling, hypersensitivity to sound in the affected ear, and impairment of taste. Twitching and weakness or paralysis of the face are the most common symptoms of this disorder.
The corner of the mouth droops, the normal wrinkles on the skin are effaced, the forehead is smooth and unfurrowed, the eye is widened and the eyelids will not close, permitting the tears to spill down the cheeks.
Researchers in Japan identified the common cold sore virus and herpes simplex as the most likely cause. It can strike almost anyone at any age; however, it disproportionately attacks pregnant women and people who have diabetes, influenza, a cold, or some other upper respiratory ailment.
The prognosis for Bell's palsy is generally very good. With or without treatment, most patients begin to get significantly better within two weeks, and about 80 percent recover completely within three months. For some, however, the symptoms may last longer. In a few cases, the symptoms may never completely disappear.
There is no specific treatment for Bell's palsy. Treatment is usually aimed at protecting the eye from drying at nighttime. Some doctors may prescribe corticosteroid medication to help reduce inflammation, anti-viral agents and an analgesic to relieve pain. In certain circumstances, surgical removal of the bone around the nerve (decompression) may be appropriate.
Reviewed by Dr Andrew Rose-Innes, MD, Department of Neurology, Yale University School of Medicine, New Haven, 2007