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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.
Investigation[edit | edit source]
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[edit | edit source]
Bell's palsy is a diagnosis of exclusion; in many cases, no specific cause can be ascertained.
Pathology[edit | edit source]
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[edit | edit source]
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 .
Treatment[edit | edit source]
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 acyclovir) to all patients with unexplained facial palsy. Surgical procedures to decompress the facial nerve have been attempted, but have not been proven beneficial. Acupuncture has also been studied, with inconclusive results.
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.
Complications[edit | edit source]
Major complications of the condition are chronic loss of taste, chronic facial spasm and corneal infections. To prevent the latter, the eyes may be protected by covers, or taped shut during sleep and for rest periods, and tear-like eye drops or eye ointments may be recommended, especially for cases with complete paralysis. Where the eye does not close completely, the reflex is also affected; great care should be taken to protect the eye from injury.
In addition, around 6% of patients exhibit crocodile tear syndrome on recovery, where they will shed tears while eating. This is thought to be due to faulty regeneration of the facial nerve, a branch of which controls the lacrimal and salivary glands.
References[edit | edit source]
[edit | edit source]
- Bell's Palsy Information Site, has a FAQ
- Bell's Palsy and Pregnancy
- Neurology Channel
- Living with Facial Palsy, a site for parents of children with Facial Palsy
- Links to pictures of Bells palsy (Hardin MD/Univ of Iowa)
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