Bell's palsy

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. more...

Symptoms

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.

Investigation

Clinicians should determine whether all branches of the facial nerve are involved, or whether the forehead muscles are spared. Since these receive innervation from both sides of the brain, the forehead can still be wrinkled by a patient whose facial palsy is caused by a problem in the brain rather than in the facial nerve itself.

Diagnosis

Bell's palsy is a diagnosis of exclusion; in many cases, no specific cause can be ascertained.

Pathology

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 (sarcoidosis, brucellosis, etc). 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.

Epidemiology

Bell's Palsy is three times more likely to strike pregnant women than non-pregnant women . It is also considered to be four times more likely to occur in diabetics than the general population, and it is more common in the elderly than children .

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