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Bell palsy

Bell palsy is paralysis of the facial muscles due to a viral infection of the seventh nerve. Though not a life threatening condition, it has tremendous impact on the patient. This is largely due to the facial disfigurement it causes.

The most common cause of unilateral facial paralysis is Bell palsy, more appropriately termed idiopathic facial paralysis. Bell palsy is an acute, unilateral, peripheral facial-nerve paralysis. It gradually improves over time in 80-90% of cases.

Bell palsy is one of the most common neurologic disorders affecting the cranial nerves. Bell palsy is more common in adults, in people with diabetes, and in pregnant women.

Etiology
Controversy surrounds the etiology of Bell palsy. The cause of Bell palsy remains to be proven. It appears to be a possible viral infection due to herpes simplex type I reactivation from cranial-nerve ganglia.

Viral infections such as herpes simplex, herpes zoster (shingles), chickenpox, mumps, mononucleosis, HIV and bacterial infections such as Lyme disease or tuberculosis can cause facial palsy. Other systemic diseases like diabetes mellitus and hypertension can also cause facial palsy. Facial palsy could be secondary to Inflammatory diseases like sarcoidosis and SLE. Infections like leprosy in our country are still common cause of facial palsy.

Clinical features
In any patient with facial weakness it is critical to differentiate whether it is a central (upper motor neuron) or peripheral (lower motor neuron) palsy. A central lesion causes weakness of the lower half of the face only (on the opposite side) while a peripheral facial palsy involves the entire half of the face (on the same side). Stroke is the most common cause for central facial palsy.

The onset is usually sudden with the patient noticing facial deviation and asymmetry while smiling or talking. Water may escape from one side of the mouth. There is difficulty in speaking. The eyes remain open, there is inability to blink and eyes become red and dry. Many people experience pain behind the ear or in the back of the head prior to onset of facial weakness. There may be a recent respiratory infection or minor viral infection prior to the onset. Some patients may notice loss of taste sensation on the affected side.

Evaluation
A lower motor neuron facial palsy is confirmed by physical examination. Thorough examination, including the ears, nose, throat, cranial nerves, must be performed. A detailed neurologic examination is a must to differentiate between central and peripheral facial palsy.

If the clinical findings are doubtful or if paralysis lasts longer than 6-8 weeks without any improvement further investigations, including gadolinium-enhanced magnetic resonance imaging of the temporal bones and pons, should be considered. Electrodiagnostic tests (facial-nerve electromyography [EMG]) may guide on the prognosis.

Treatment
Treatment of Bell palsy is conservative and guided by the severity in a particular case. Studies have shown the benefit of early (within 72 hours) high-dose corticosteroids for acute Bell palsy. Although antiviral treatment (famcilclovir, acyclovir) has been used in recent years, evidence is now available indicating that it may not be useful.

Lubricating eye drops for dry eye with ocular taping is helpful to protect the cornea from exposure. Physiotherapy with facial muscle exercises and nerve stimulation may be useful.

Surgical therapy with transposition of temporalis muscle and reinnervation of facial nerve by facial nerve grafting can be used in patients with permanent facial paralysis.

Prognosis
The natural course of Bell palsy varies from early complete recovery to permanent paralysis. Patients generally have a good prognosis; approximately 80-90% recover without noticeable disfigurement within 6 weeks to 3 months. If some restoration of function is noted within 3 weeks, then the recovery is most likely to be complete.

The risk factors thought to be associated with a poor outcome in patients with Bell palsy are (1) age greater than 60 years (2) complete paralysis (3) decreased taste on the side of paralysis. (4) axonal degeneration on electrophysiology studies. Other factors thought to be associated with poor outcome include pain in the posterior auricular area.

Patients with recurrent facial palsy should undergo MRI to rule out a neoplastic or inflammatory (eg, multiple sclerosis, sarcoidosis).