Bell’s palsy also called facial 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 psychological impact on the patient. This is largely due to the facial disfigurement it causes. There is apprehension in the patients mind that hemiplegia may ensue following facial palsy.

The most common cause of unilateral facial paralysis is Bell’s palsy, more appropriately termed idiopathic facial paralysis. Bell’s palsy is an acute, unilateral, peripheral facial-nerve paralysis. It gradually improves over time in 80-90% of cases. Bell’s palsy is one of the most common neurologic disorders affecting the cranial nerves. Bell’s palsy is more common in adults, in people with diabetes, and in pregnant women.

Etiology

Controversy surrounds the etiology of Bell’s palsy. The cause of Bell’s 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 to the unaffected side and asymmetry while smiling or talking. Water may escape from the affected side of the mouth, and this may be the first symptom noticed by the patient. There is difficulty in speaking. The eyes on the affected side 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. One has to carefully look for vesicles in the auditory canal and external ear, seen in Ramsay Hunt syndrome (geniculate Herpes). 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’s 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’s palsy. Although antiviral treatment (famcilclovir, acyclovir) has been used in recent years, evidence is now available indicating that it may not be useful. A combination of steroids with antivirals is usually prescribed.

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.