Bell Palsy

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An acute, usually unilateral, peripheral facial nerve palsy of unknown etiology. Herpes-mediated viral inflammatory/immune mechanism is the likely cause of most cases, causing subsequent swelling and compression of cranial nerve VII (facial) and the associated vasa nervorum.


  • Affects 0.002% of the population annually
  • No race, geographic, or gender predominance
  • Median age of onset is 40 years but affects all ages.
  • Accounts for about half of all cases of unilateral facial paralysis
  • Occurs with equal frequency on the left and right sides of the face
  • Most patients recover, but as many as 30% are left with facial disfigurement and pain.

  • 25 to 30 cases per 100,000 people in the United States per year
  • Lowest in children ≤10 years of age; highest in adults ≥70 years of age
  • Higher among pregnant women (3 times the risk)

Affects 40,000 Americans every year

Etiology and Pathophysiology

  • Results from damage to the facial cranial nerve (VII)
  • Exact pathogenesis is still controversial; infective, immune, and ischemic mechanisms are potential contributors.
  • The most likely cause is activation of latent herpes virus (herpes simplex virus [HSV] type 1 and herpes zoster virus) in cranial nerve ganglia.
  • Inflammation of cranial nerve VII causes swelling and subsequent compression and possibly demyelination of both the nerve and the associated vasa nervorum.
  • Ischemia from arteriosclerosis associated with diabetes mellitus

May be associated with a genetic predisposition, but it remains unclear, which factors are inherited

Risk Factors

  • Pregnancy, especially in the 3rd trimester or in the 1st postpartum week
  • Immunocompromised status
  • Diabetes mellitus, possibly secondary to microvascular ischemia
  • Age >30 years
  • Exposure to cold temperatures
  • Upper respiratory infection (e.g., coryza, influenza)
  • Chronic hypertension (HTN)
  • Obesity
  • Migraine headache

Commonly Associated Conditions

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

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