Bell's palsy

Bell's palsy is a paralysis of the facial nerve resulting in inability to control facial muscles on the affected side. Several conditions can cause a facial paralysis, e.g., brain tumor, stroke, and Lyme disease. However, if no specific cause can be identified, the condition is known as Bell's Palsy. Named after Scottish anatomist Charles Bell, who first described it, Bell's palsy is the most common acute mononeuropathy (disease involving only one nerve), and is the most common cause of acute facial nerve paralysis.

Bell's palsy is defined as an idiopathic unilateral facial nerve paralysis, usually self-limiting. The trademark is rapid onset of partial or complete palsy, usually in a single day.

It is thought that an inflammatory condition leads to swelling of the facial nerve (nervus facialis). The nerve travels through the skull in a narrow bone canal beneath the ear. Nerve swelling and compression in the narrow bone canal are thought to lead to nerve inhibition, damage or death. No readily identifiable cause for Bell's palsy has been found, but clinical and experimental evidence suggests herpes simplex type 1 infection may play a role.

Doctors may prescribe anti-inflammatory and anti-viral drugs. Early treatment is necessary for the drug therapy to have effect. The effect of treatment is still controversial. Most people recover spontaneously and achieve near-normal functions. Many show signs of improvement as early as 10 days after the onset, even without treatment.

Often the eye in the affected side cannot be closed. The eye must be protected from drying up, or the cornea may be permanently damaged resulting in impaired vision.

Symptoms:
Although defined as a mononeuritis (involving only one nerve), patients diagnosed with Bell’s palsy may have "myriad neurological symptoms" including "facial tingling, moderate or severe headache/neck pain, memory problems, balance problems, ipsilateral limb paresthesias, ipsilateral limb weakness, and a sense of clumsiness" that are "unexplained by facial nerve dysfunction". This is yet an enigmatic facet of this condition.

Diagnosis:
Bell's palsy is a diagnosis of exclusion; by elimination of other reasonable possibilities. Therefore, by definition, no specific cause can be ascertained. Bell's palsy is commonly referred to as idiopathic or cryptogenic, meaning that it is due to unknown causes. Being a residual diagnostic category, the Bell's Palsy diagnosis likely spans different conditions which our current level of medical knowledge cannot distinguish. This may inject fundamental uncertainty into the discussion below of etiology, treatment options, recovery patterns etc. See also the section below on Other symptoms. Studies show that a large number of patients (45%) are not referred to a specialist, which suggests that Bell’s palsy is considered by physicians to be a straightforward diagnosis that is easy to manage. A significant number of cases are misdiagnosed. This is unsurprising from a diagnosis of exclusion, which depends on a thorough investigation.

Treatment:
Treatment is a matter of controversy. In patients presenting with incomplete facial palsy, where the prognosis for recovery is very good, treatment may be unnecessary. However, patients presenting with complete paralysis, marked by an inability to close the eyes and mouth on the involved side, are usually treated with anti-inflammatory corticosteroids. Prednisolone, a corticosteroid, if used early in treatment of Bell's palsy, significantly improves the chances of complete recovery at 3 and 9 months when compared to treatment with acyclovir, an anti-viral drug, or no treatment at all. The likely association of Bell's palsy with the herpes virus has led most American neurologists to prescribe a course of anti-viral medication (such as acyclovir) to all patients with unexplained facial palsy, although a large study showed no additional benefit from acyclovir beyond that from prednisolone alone. Surgical procedures to decompress the facial nerve have been attempted, but have not been proven beneficial. Acupuncture has also been studied, with inconclusive results.

A practice parameter from the American Academy of Neurology states that "corticosteroids are safe and probably effective, and that acyclovir is safe and possibly effective". Early treatment (ie, within 3 days after the onset) is necessary for acyclovir-prednisone therapy to be effective. If the patient presents 10 days after the onset of symptoms, no drug treatment is necessary.