Bell's palsy...

Two weeks after a viral illness, a 9-year-old boy presents to your clinic with a complaint of several days of weakness of his mouth. In addition to the drooping of the left side of his mouth, you note that he is unable to completely shut his left eye. His smile is asymmetric, but his examination is otherwise normal.
Which of the following is the most likely diagnosis?
a. Guillain-Barré syndrome
b. Botulism
c. Cerebral vascular accident
d. Brainstem tumor
e. Bell palsy

Answer: e. Bell palsy

Discussion:

Bell palsy is an acute, unilateral facial nerve palsy that begins about 2 weeks after a viral infection. Although the exact pathophysiology is unknown, reactivation of herpes simplex or varicella-zoster virus seems to be the most common cause; demyelination through an autoimmune process or allergic inflammation may also play a part in some cases. On the affected side, the upper and lower face are typically paretic, the mouth droops, and the patient cannot close the eye.


Treatment consists of maintaining moisture to the affected eye (especially at night) to prevent keratitis.

Complete, spontaneous resolution occurs in about 85% of cases, 10% of cases have mild residual disease, and about 5% of cases do not resolve.

Occasionally infants will have facial nerve palsy at birth; this is usually related to compression from forceps and spontaneously resolves over several weeks. As this is a compression neuropathy, it should not be called congenital Bell palsy.

When evaluating a facial weakness, special care must be taken to evaluate the movement of the forehead. A peripheral facial neuropathy like Bell palsy will cause upper and lower facial weakness on the affected side. However, a central facial palsy will spare the forehead due to bilateral innervation.