Description

An acute, usually unilateral, self-limiting peripheral (lower motor neuron) facial nerve (cranial nerve VII) palsy of largely idiopathic etiology. It results in the inability to voluntarily move the facial muscles of the affected side. Ischemic, immune, and infectious processes have been posited as likely mechanisms for Bell palsy.

Epidemiology

• No race, geographic, or gender predominance
• Affects all aged, with the highest incidence being in patients aged 15 to 45 years.
• Occurs with equal frequency on the left and right sides of the face

Incidence
Global studies have demonstrated annual incidence of up to 53 per 100,000.

Etiology and Pathophysiology

• Inflammation of cranial nerve VII causes edema of perineurium and subsequent compression and possibly degeneration of both the nerve and the associated vasa nervorum.
• Activation of latent herpes virus (herpes simplex virus type 1 and herpes zoster virus) in cranial nerve ganglia thought to account for many cases of Bell palsy.

Risk Factors

• Pregnancy, with increased risk seen in patients with chronic hypertension, maternal obesity, and severe preeclampsia
• Immunocompromised status
• Diabetes mellitus
• Age >30 years
• Upper respiratory infection
• Chronic hypertension
• Obesity
• Extremes of temperature (1)