Bell's Palsy — Detailed Overview

Definition

Anatomy Recap

Etiology & Pathophysiology

• The nerve undergoes inflammation with mononuclear cell infiltration, consistent with infectious or immune-mediated injury.
• Herpes simplex virus type 1 (HSV-1) is the most commonly implicated pathogen — its DNA has been detected in endoneurial fluid and posterior auricular muscle, suggesting reactivation in the geniculate ganglion.
• Varicella-zoster virus (VZV) accounts for up to 1/3 of cases and is the second most frequent cause (when VZV is found with vesicles, the entity is called Ramsay Hunt Syndrome).
• Other viruses (EBV, CMV, adenovirus) and HIV seroconversion can also cause Bell's palsy.
• Inflammation causes edema within the bony facial canal, leading to nerve compression and ischemia.

Risk Factors

Clinical Features

Key Presenting Symptoms

• Acute-onset unilateral facial weakness/paralysis — develops over hours to a few days
• Inability to close the eye on the affected side (lagophthalmos)
• Flattening of the nasolabial fold
• Drooping of the mouth corner, with deviation of mouth to unaffected side
• Loss or reduction of taste on anterior 2/3 of tongue (chorda tympani involvement)
• Hyperacusis (sensitivity to sound) due to stapedius muscle paralysis
• Post-auricular pain or numbness (often precedes the palsy by 1–2 days)
• Decreased lacrimation or, paradoxically, excessive tearing (crocodile tears — from aberrant regeneration)

Critical Distinguishing Feature: Upper vs. Lower Motor Neuron Lesion

Forehead sparing = central cause until proven otherwise. Bell's palsy always involves the forehead.

Clinical Image

Grading — House-Brackmann Scale

Diagnosis

Workup

• History & physical: Look for vesicles (Ramsay Hunt), otitis media, parotid mass, tick bite (Lyme), or systemic features (sarcoidosis, lymphoma).
• Blood tests: Consider Lyme serology in endemic areas, blood glucose, CBC.
• MRI with gadolinium: Indicated if:
  • Atypical features or slow progression (>3 weeks)
  • No improvement by 4 months
  • Recurrent ipsilateral palsy
  • Other cranial nerve deficits
• EMG/Nerve conduction studies: Used to assess severity and prognosis after 2–3 weeks.

Differential Diagnosis

Treatment

1. Corticosteroids (First-line)

• Prednisone 60–80 mg/day for the first 5 days, then tapered over the next 5 days.
• Modestly shortens recovery and improves functional outcome.
• Most effective when started within 72 hours of symptom onset.

2. Antivirals

• Large, well-controlled RCTs found no added benefit of valacyclovir (1000 mg/day × 5–7 days) or acyclovir (400 mg 5× daily × 10 days) over steroids alone in typical Bell's palsy.
• Use antivirals if vesicular lesions are present in the palate or external auditory canal (suggesting VZV/Ramsay Hunt) — in that setting, combination therapy is standard.

3. Eye Care (Critical)

• Paper tape over the eyelid at night to prevent corneal exposure.
• Artificial tears during the day.
• Consider a moisture chamber or eye patch.
• Ophthalmology referral if corneal exposure develops.

4. Physiotherapy

• Gentle massage of weakened muscles helps prevent contracture.
• Facial exercises during recovery.

5. Surgical Options

• For permanent paralysis: cosmetic procedures (e.g., facial reanimation surgery, gold weight implant in upper eyelid, brow lift).
• Surgical decompression of the facial nerve is controversial and rarely performed.

Prognosis

• ~70–80% of patients recover completely without treatment.
• With steroid treatment, recovery rates improve further.
• Recovery usually begins within 3–4 weeks and is complete by 3–6 months in most.
• Poor prognostic indicators:
  • Complete paralysis at onset
  • Age > 60 years
  • Severe pain
  • No recovery within 3 weeks
  • Diabetes mellitus

Complications

Special Populations

• Pregnancy: Steroids are used cautiously; most cases recover well.
• Children: Better prognosis than adults; generally recover fully.
• Bilateral palsy: Should prompt workup for Lyme disease, sarcoidosis, Guillain-Barré, or HIV — bilateral Bell's palsy is rare and demands investigation.