Description

A peripheral lower motor neuron facial palsy, usually unilateral, which arises secondary to inflammation and subsequent swelling and compression of cranial nerve VII (facial) and the associated vasa nervorum

Epidemiology

• Affects 0.02% of the population annually
• Most patients recover, but as many as 30% are left with facial disfigurement and pain.
• Accounts for 60–75% of all cases of unilateral facial paralysis
• Median age of onset is 40 years, but affects all ages
• Predominant sex: Equal occurrence in men and women
• Occurs with equal frequency on the left and right sides of the face

• 20–30 cases per 100,000 people in the US per year
• Lowest in children ≤10 years of age; highest in people ≥70 years of age
• Higher among pregnant women

Prevalence
Affects 40,000 Americans every year

Risk Factors

• Pregnancy
• Diabetes mellitus
• Age >30 years
• Exposure to cold temperatures
• Upper respiratory infection (e.g., coryza, influenza)

Genetics
A genetic predisposition may be associated with Bell palsy, but it is unclear which factors are inherited.

Etiology

• Results from damage to the facial cranial nerve (VII)
• Inflammation of cranial nerve VII causes swelling and subsequent compression of both the nerve and the associated vasa nervorum.
• May arise secondary to reactivation of latent herpes virus (herpes simplex virus [HSV] type 1 and herpes zoster virus) in cranial nerve ganglia or because of ischemia from arteriosclerosis associated with diabetes mellitus

Commonly Associated Conditions

• HSV
• Lyme disease
• Diabetes mellitus
• Hypertension
• Herpes zoster virus
• Ramsay-Hunt syndrome
• Sjögren syndrome
• Sarcoidosis
• Eclampsia
• Amyloidosis