Bell Palsy

Idiopathic acute unilateral lower motor neuron facial nerve paralysis.

Source: WHO / CDC / NIH Evidence Guidelines

Updated: Aug 11, 2026

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Red Flag Warning & Emergency Situations

Emergency Management: Facial palsy accompanied by aphasia or hemiparesis requires stroke code.

Core Definition:

Acute, unilateral, lower motor neuron facial nerve (CN VII) paralysis. It causes facial muscle weakness and is typically considered idiopathic, though HSV-1 reactivation is heavily implicated.

Detailed Overview

Bell palsy accounts for most facial nerve palsies, presenting with rapid onset weakness over 48-72 hours. Inflammation and edema of the facial nerve within the narrow fallopian canal lead to compression and demyelination. Timely oral corticosteroids within 72 hours improve recovery rates.

Epidemiology & Demographics

Incidence 15-30 per 100,000 annually. Affects sexes equally. 3x higher risk during the 3rd trimester of pregnancy and early postpartum.

Etiological Mechanism

Idiopathic; strong evidence points to reactivation of Herpes Simplex Virus 1 (HSV-1) or Varicella Zoster Virus (VZV) in the geniculate ganglion.

Primary Causes

Primary: Idiopathic. Secondary triggers: URI, stress, cold exposure.

Latent HSV-1 in the geniculate ganglion reactivates, causing neural edema. The facial nerve traverses the rigid temporal bone; edema causes ischemia and demyelination. Severe compression can cause Wallerian degeneration.

Diagnostic Criteria & Guidelines

Clinical diagnosis: sudden onset unilateral LMN facial palsy involving forehead, absent other focal neurologic deficits.

First-Line Treatment:

Prednisone 60 mg PO daily for 5 days, then 5-day taper. Eye lubrication with artificial tears q1-2h and nightly ophthalmic ointment.

Second-Line & Adjunctive Therapy

Valacyclovir 1000 mg PO TID for 7 days (added for severe cases HB grade IV or higher).

Surgical & Procedural Management

Surgical facial nerve decompression via middle cranial fossa approach if >90% degeneration on ENoG within 14 days.

Patient Counseling & Advice

Reassure that a stroke has been ruled out. Symptoms peak in 72 hours; improvement takes 3-4 weeks.

Follow-Up & Monitoring Schedule

Re-evaluate in 48-72 hours for eye care, then at 1 month to assess motor recovery.

Preventive Strategies

No proven prevention; early treatment of triggers like shingles.

71% recover completely without treatment; >80% recover completely with early steroids.

Authoritative Sources & Evidence References

World Health Organization (WHO) & CDC Guidelines: Information compiled from current international clinical practice guidelines.