Neurology · MU Sofia

37. Bell's palsy

Explains Bell's palsy as an acute, idiopathic lower motor neuron facial nerve palsy, starting with a brief recap of what the facial nerve supplies. It then covers the inflammatory mechanism, the sudden-onset features and the additional signs such as hyperacusis and taste loss. A comparison table sets lower and upper motor neuron facial palsy side by side, followed by examination findings, secondary causes, differential diagnoses, prognosis, treatment and complications.

Inside: 1 section · 1 table · 16 flashcards · 2 min

Topic 37 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 239 words (2 min of reading), with 16 flashcards.

In this note

  1. Bell’s palsy

Bell’s palsy

Definition: Bell’s palsy is an acute idiopathic lower motor neuron (LMN) palsy of the facial nerve (CN VII) causing unilateral facial weakness.

Anatomy Reminder (CN VII)

Facial nerve controls: Facial expression muscles. Taste (anterior 2/3 tongue). Lacrimation and salivation. Stapedius muscle (hearing modulation)

Pathophysiology

  • Most commonly due to inflammation and edema of CN VII in the facial canal
  • Often linked to viral reactivation (e.g., herpes viruses)

Clinical Features

Sudden Onset: Develops over hours to 1–2 days

Ipsilateral LMN Facial Paralysis (key sign): Inability to wrinkle forehead. Inability to close eye (lagophthalmos). Drooping of mouth corner. Loss of nasolabial fold. Food accumulation in cheek

Additional Features

  • Hyperacusis (sound sensitivity) → stapedius paralysis
  • Loss of taste (anterior 2/3 tongue)
  • Reduced lacrimation and salivation
  • Dry eye or mouth

Key Distinction

LMN vs UMN Facial Palsy

Examination Findings

  • Complete unilateral facial weakness
  • Bell phenomenon (eye rolls upward when attempting closure)
  • Loss of corneal reflex efferent limb (CN VII)

Causes (Secondary Bell-like palsy)

  • Viral infection (HSV-1 most common association). Diabetes mellitus. Pregnancy. Lyme disease (important differential). Tumors (if progressive or recurrent)

Differential Diagnosis: Stroke (central facial palsy). Brainstem lesions. Parotid gland tumor. Lyme disease neuropathy

Prognosis

  • Most patients recover within weeks to months
  • Recovery may be incomplete in severe cases

Treatment

Medical: Corticosteroids (first-line). Antivirals (e.g., acyclovir) in selected cases.

Eye protection (VERY IMPORTANT): Artificial tears. Eye patch at night. Lubricating ointments

Complications: Synkinesis (abnormal reinnervation). Facial contractures. Persistent weakness. Crocodile tears (gustatory lacrimation)

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