Bell's palsy (facial palsy) is characterised by facial drooping on the affected half, due to malfunction of the facial nerve (VII cranial nerve), which controls the muscles of the face. 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. The paralysis is of the infranuclear/lower motor neuron type. Bell’s palsy affects about 40,000 people in the United States every year. It affects approximately 1 person in 65 during a lifetime. Until recently, its cause was unknown in most cases, but it has now been related to both Lyme disease and Herpes simplex. Bell's palsy can return unexpectedly.
Additional symptoms that may accompany the condition are pain around the ear and loss of taste. In the great majority of patients, only one side of the face is affected. Detection of sensory loss, hearing loss, or ataxia during examination militates against the diagnosis of Bell's palsy and suggests the need for further evaluation.
Treatment is a matter of controversy. In patients presenting with incomplete facial palsy, 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. The efficacy of this treatment has not been reliably demonstrated. 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 aciclovir) to all patients with unexplained such facial palsy. Surgical procedures to decompress the facial nerve have been attempted, but have not been proven beneficial.
Although most patients (60–80%) recover completely from Bell's palsy within several weeks, some require several months, and others may be left with deficits of varying degrees.