Bell's Palsy

Bell's palsy is characterised by facial drooping on the affected half, due to malfunction of the facial 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, 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.

It is supposed to be the result of inflammation of the facial nerve, which produces pressure on the nerve as it exits the skull within its bony canal. Patients with facial palsy for which an underlying cause can be readily found are not generally considered to have Bell's palsy per se. These underlying problems include tumor, meningitis, stroke, diabetes mellitus, head trauma and inflammatory diseases of the cranial nerves. In these conditions, the neurologic findings are rarely restricted to the facial nerve. Babies can be born with facial palsy, and they exhibit many of the same symptoms as people with Bell's palsy; this is often due to a traumatic birth which causes irrepairable damage to the facial nerve, i.e. acute facial nerve paralysis.

One disease that may be difficult to exclude in the differential diagnosis is involvement of the facial nerve in infections with the herpes zoster virus. The major differences in this condition are the presence of small blisters, or vesicles, of the external ear and hearing disturbances, but these findings may occasionally be lacking.

In recent years, two new suspects have been added to the possible causes of Bell's palsy. Lyme disease may produce the typical palsy, and may be easily diagnosed by looking for Lyme-specific antibodies in the blood. In endemic areas Lyme disease may be the most common cause of facial palsy. The subsequent observation of an increased incidence of antibodies to the Herpes simplex virus in patients with Bell's palsy has led many specialists to believe that this agent is the most likely underlying cause in areas where Lyme disease is uncommon.

...More at Wikipedia

Related Links:

• US National Library of Medicine
• Mayo Clinic

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