The "Bell's smile" is characterized by an asymmetry caused by paralysis of one side of the face.

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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...

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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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New concepts in Bell's palsy improve treatment options
From American Family Physician, 7/1/05 by Anne D. Walling

Bell's palsy affects about one in 60 persons and has an annual incidence of around 20 per 100,000 persons. Overall, the condition is most common in persons 15 to 45 years of age, but the incidence is particularly high in pregnant women (45 per 100,000). Holland and Weiner outlined recent developments concerning the management of Bell's palsy.

Although still somewhat controversial, evidence is accumulating that reactivated herpes viruses (simplex type 1 or zoster) in cranial nerve ganglia are the most common cause of Bell's palsy. Conditions caused by the herpes zoster virus may be more severe than those caused by herpes simplex virus type 1.

Patients usually are alarmed by the sudden onset of Bell's palsy symptoms, which include facial weakness accompanied by change in taste sensation, hyperacusis, and decreased lacrimation. Some patients report ear pain or fullness before the paralysis. Severe pain is more typical of herpes zoster infections. Examination of a patient with Bell's palsy shows impaired facial and platysma muscles causing drooping of the mouth and brow plus difficulty closing the eye or mouth. The patient should be examined for evidence of other causes of lower facial weakness such as intracranial or parotid lesions or Lyme disease. Laboratory tests are not helpful in diagnosis except to exclude other potential causes of facial weakness.

Approximately 75 percent of patients recover fully from Bell's palsy, and 10 percent have minor sequelae. About one sixth of patients have residual moderate to severe weakness, contracture, spasm, or synkinesis. In patients who do not receive treatment, most improvement occurs within three weeks. Additional improvement is delayed for the four to six months required for nerve regeneration. Although prognosis cannot be predicted accurately, factors associated with poor outcome have been identified in the accompanying table.

The goals of treatment are to accelerate recovery and prevent or minimize complications. Patients may require considerable reassurance and support during this illness. The eye should be protected from drying by hourly use of lubricating drops while awake and eye ointment at night. Massage, facial exercises, and biofeedback can contribute to improvement but have not been studied extensively. Steroids have been shown to increase the proportion of patients with good outcome by 17 percent if used within seven days of symptom onset. Antiviral agents, such as acyclovir (Zovirax), are increasingly recommended in combination with steroids because of the accumulating evidence of a viral etiology of Bell's palsy. Because acyclovir has low bioavailability, studies are focusing on valacyclovir (Valtrex) and famciclovir (Famvir). One prospective controlled study showed enhanced recovery when valacyclovir was combined with prednisone. The effect was particularly noticeable in older patients. Ideally, patients should begin treatment within 72 hours of symptom onset. Surgical decompression is reserved for rare cases because of danger of adverse effects.

The authors conclude that patients with Bell's palsy should begin treatment immediately and be referred to a subspecialist. Patients with significant sequelae should be referred for multidisciplinary management that could include injections of botulinum toxin, facial reanimation, and cosmetic surgery.

Holland NJ, Weiner GM. Recent developments in Bell's palsy. BMJ September 4, 2004;329:553-7.

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