What is the difference between a stroke and Bell's palsy?

Differences Between Stroke and Bell's Palsy

Bell's palsy is an acute unilateral facial nerve paresis or paralysis with onset in less than 72 hours and without identifiable cause, while stroke causing facial weakness typically presents with additional neurological symptoms and different facial involvement patterns. 1

Key Distinguishing Features

Bell's Palsy

• Onset and Timing:

  • Rapid onset (<72 hours)
  • Progression may occur over 48 hours 2
  • Typically affects the entire side of the face (forehead, eye, and mouth)

• Clinical Presentation:

  • Complete inability to move facial muscles on affected side (facial paralysis) or partial weakness (facial paresis) 1
  • Affects all facial muscles on one side, including the forehead
  • May include:
    • Ipsilateral pain around ear or face
    • Hyperacusis (increased sensitivity to sound)
    • Taste disturbance
    • Dryness of eye or mouth 1

• Cause:

  • Idiopathic (no identifiable cause)
  • Suspected viral etiology with facial nerve inflammation and edema 1
  • Occurs when the facial nerve (cranial nerve VII) is compressed within the narrow canal of the temporal bone

Stroke

• Onset and Timing:

  • Sudden onset
  • Usually does not progress after initial presentation

• Clinical Presentation:

  • Facial weakness typically spares the forehead (central/upper motor neuron pattern)
  • Usually accompanied by other neurological deficits:
    • Limb weakness
    • Speech disturbance
    • Visual changes
    • Balance problems
    • Sensory changes 3

• Cause:

  • Vascular event (ischemic or hemorrhagic)
  • Pontine stroke can rarely present with isolated facial weakness mimicking Bell's palsy 3

Diagnostic Considerations

When to Suspect Stroke Instead of Bell's Palsy

• Forehead sparing (patient can still wrinkle forehead on affected side)
• Presence of other neurological deficits
• Gradual progression beyond 72 hours
• History of stroke risk factors (diabetes, hypertension, hypercholesterolaemia) 3
• Presence of vertigo, headache, or other neurological symptoms 3

Red Flags Requiring Urgent Evaluation

• Bilateral facial weakness (Bell's palsy is typically unilateral) 1
• Gradual onset over more than 72 hours
• Other cranial nerve involvement
• Presence of additional neurological symptoms 4

Diagnostic Approach

1. Thorough History and Physical Examination:

   • Document timing and progression of symptoms
   • Assess all cranial nerves
   • Test facial movement patterns (especially forehead involvement)
   • Look for other neurological deficits 1

2. Diagnostic Testing:

   • Routine laboratory testing is not recommended for typical Bell's palsy 1, 5
   • Imaging is not routinely recommended for Bell's palsy but is essential if stroke is suspected 1, 5
   • Consider MRI if pontine stroke is suspected, noting that small pontine infarcts can be challenging to identify 3

Management Differences

Bell's Palsy Management:

• Oral corticosteroids within 72 hours of symptom onset (strongly recommended) 5
• Consider antiviral therapy in combination with steroids 5
• Eye protection measures for patients with incomplete eye closure 5
• Most patients (70-94%) recover completely without treatment 5

Stroke Management:

• Urgent neurological evaluation
• Time-sensitive interventions for ischemic stroke
• Secondary prevention strategies
• Rehabilitation for residual deficits

Common Pitfalls to Avoid

1. Misdiagnosing stroke as Bell's palsy:

   • Always assess for other neurological symptoms
   • Remember that pontine stroke can rarely present with isolated facial weakness 3

2. Failing to recognize the pattern of facial weakness:

   • Bell's palsy: entire side of face including forehead
   • Stroke: typically spares the forehead (central pattern)

3. Delaying treatment:

   • Both conditions benefit from prompt intervention
   • Corticosteroids for Bell's palsy are most effective when started within 72 hours 5
   • Stroke treatment is time-critical

Remember that approximately 30% of patients presenting with facial paresis/paralysis have underlying causes other than Bell's palsy, making careful differential diagnosis essential 1.