Bell's Palsy vs Stroke: Key Diagnostic Differences
The critical distinction is that Bell's palsy causes weakness of BOTH the upper and lower face (including forehead), while stroke causes weakness of only the lower face with forehead sparing due to bilateral cortical innervation of the upper facial muscles. 1, 2
Primary Diagnostic Features
Bell's Palsy Characteristics
- Unilateral facial weakness involving the forehead (inability to raise eyebrow, wrinkle forehead on affected side) 2, 3
- Rapid onset over less than 72 hours 2
- Patient can close eye on affected side (though incompletely) 2
- Loss of nasolabial fold, drooping corner of mouth, drooling 4
- May have ipsilateral ear/face pain, hyperacusis, taste disturbance on anterior two-thirds of tongue 2
- No other neurological deficits (no limb weakness, no sensory changes, no diplopia, no dysphagia) 5
Stroke (Central Facial Weakness) Characteristics
- Forehead is spared - patient CAN raise eyebrow and wrinkle forehead on affected side 1
- Lower face weakness only (cannot smile symmetrically, mouth droops) 1
- Red flag symptoms: dizziness, dysphagia, diplopia, contralateral limb weakness or numbness 5, 6
- Other cranial nerve involvement suggests central pathology 5
- May have gaze palsy, nystagmus, or ataxia 6
Critical Clinical Pitfall
Rare pontine strokes can mimic Bell's palsy by causing both upper AND lower facial weakness. 6, 7 These cases are distinguished by:
- Severe dysphagia 6
- Contralateral face and arm numbness 6
- Diplopia or vertigo 6
- Gaze abnormalities or nystagmus 6
- Encephalopathy or altered mental status 7
Diagnostic Approach
History Red Flags Against Bell's Palsy
- Symptom progression beyond 72 hours (suggests tumor or infection) 5
- Bilateral facial weakness (extremely rare in Bell's palsy; consider Guillain-Barré or sarcoidosis) 1, 2
- History of head/neck cancer 2
- Isolated branch paralysis rather than complete hemifacial involvement 2
Physical Examination Algorithm
Test forehead function: Ask patient to raise eyebrows and wrinkle forehead 2
- If forehead SPARED → stroke until proven otherwise
- If forehead INVOLVED → likely Bell's palsy but continue evaluation
Assess all cranial nerves: Document function of cranial nerves II-XII 5
- Any other cranial nerve deficit → NOT Bell's palsy 5
Check for stroke symptoms: Evaluate for limb weakness, sensory deficits, speech abnormalities, gait disturbance 5, 6
- Any present → urgent stroke evaluation
Examine ear and parotid region: Look for vesicles (Ramsay Hunt), masses, trauma 5, 1
Testing Recommendations
- Routine laboratory testing is NOT recommended for typical Bell's palsy presentation 5
- Lyme serology should be obtained in endemic areas or recent travel to endemic regions 5, 8
- Diagnostic imaging is NOT routinely indicated for Bell's palsy 5
- MRI brain should be obtained if any atypical features, other neurological symptoms, or concern for stroke 8, 6, 7
Treatment Differences
Bell's Palsy Treatment
- Oral corticosteroids within 72 hours of onset (83% recovery at 3 months vs 63.6% with placebo) 8
- Eye protection is mandatory: lubricating drops, ointments, moisture chambers, eye patching, sunglasses 2
- Antivirals may reduce synkinesis 9
- Most patients (70% with complete paralysis, 94% with incomplete) recover fully within 6 months 2
Stroke Treatment
- Immediate activation of stroke protocol
- Time-sensitive thrombolytic therapy or thrombectomy if eligible
- Admission for monitoring and secondary prevention
Follow-Up Mandates
Reassess or refer to specialist if: 8, 2
- New or worsening neurological findings
- No improvement within 2-3 weeks
- Incomplete recovery at 3 months
- Development of ocular symptoms