Bell's Palsy: Causes, Symptoms, and Treatment

Introduction

A person might wake up one morning and discover that one side of his or her face shows signs of paralysis. The symmetrical nature of the face might present a mismatched appearance, with the afflicted side exhibiting varying levels of deformity and droopiness.

The person might find that he or she is unable to close the eye on the affected side. The paralysis of one side of the face means that speech is often distorted. Feeding becomes difficult. Drooling is frequent. The person finds it impossible to pucker the lips into the shape used for whistling. The direct diagnosis for this set of symptoms is Bell's Palsy. This condition is relatively temporary, and only a small number of those who suffer from it experience permanent effects. Bell's Palsy can develop over a few hours or a few days; it is not uncommon for a person to find that the condition has appeared overnight.

Origins

Sir Charles Bell, a Scottish physician, first described the condition in the 19th century. The paralysis that results from Bell's Palsy often leads those afflicted to fear that they have suffered a stroke. This is not the case. Bell's Palsy occurs as a result of damage to the facial nerves. The nerves are disrupted and typical stimuli are interrupted or distorted; the brain does not process the disrupted information effectively, leading to paralysis. Because the damage occurs to one nerve of the paired facial nerves, the paralysis and other symptoms affect only the side of the face where the nerve has been damaged. There is no preference for the left or right side, and the chances of the condition affecting both sides of the face simultaneously are rare.

Causes and Epidemiology

The causes of Bell's Palsy have not been directly identified. They are generally associated with anything that might cause damage to the nerves, and inflammation in the area of the nerves is a frequent culprit. This inflammation may be triggered by infections from the common cold virus or herpes simplex. Some researchers have pointed to herpes meningitis as a potential cause as well. The inflammation creates pressure on the Fallopian canal — a bony conduit that covers most of the facial nerve — which damages the nerve. In other cases, pressure on the nerves disrupts the flow of oxygen and blood to the area.

Diabetics are particularly susceptible to the condition, being almost four times as likely to develop it as non-diabetics. High blood pressure, meningitis, mechanical injuries to the face and head, prolonged middle ear infections, and chronic headaches have all been implicated as contributing factors. People who have recently had influenza or a cold are more susceptible than others. It is estimated that approximately 25 in every 100,000 people will suffer from Bell's Palsy. The condition does not discriminate based on sex; women are as likely as men to suffer from it. Pregnant women, especially in the third trimester, are particularly susceptible, as are elderly individuals above the age of sixty (Singhi and Jain, 2003).

The National Institute of Neurological Disorders and Stroke (NINDS), a branch of the National Institutes of Health, reports that there may be a genetic susceptibility to Bell's Palsy (NINDS, 2004). Those suffering from inflammatory diseases such as sarcoidosis, or from immune system diseases such as HIV, are also at greater risk.

Although there is no specific cure for the condition and most medications treat the symptoms rather than the cause, the prognosis for Bell's Palsy is generally positive. Recovery takes as long as the facial nerve requires to heal. Most patients fully recover within a few weeks, and signs of recovery can appear as early as one to two weeks after onset. In some cases, recovery may take up to a year, and on rare occasions permanent damage is observed. Recurrence of the condition occurs in approximately seven percent of patients.

Cellular Mechanisms

There are twelve cranial nerves in the human head. These nerves receive impulses and direct the reactions that control most of our facial muscles — the expressions we produce when happy or sad are all governed by the cranial nerves. While damage to any one of these nerves can result in Bell's Palsy, the nerve most commonly implicated is the seventh cranial nerve, also called the facial nerve. It is a symmetrically paired nerve that emerges from its nerve center in the brain, travels through the Fallopian canal beneath the ear, and enervates various muscles on either side of the face (AAO-HNS, 2004). The Fallopian canal encloses the nerve for most of its length. As with most nerves, a protective covering called the myelin sheath also surrounds it. Milder forms of Bell's Palsy occur when the damage is limited to this sheath.

The facial nerve specifically controls facial expressions of sorrow, annoyance, and happiness. It also governs the blinking of the eyes — one of the symptoms that requires active treatment — as well as the function of the stapes, the smallest bone in the body, which is responsible for balance. Additionally, the facial nerve controls taste sensations in the tongue and regulates the salivary glands, which explains the drooling that is characteristic of the condition.