How do you differentiate and manage Bell's palsy vs stroke in the differential diagnosis?

Differentiating Bell's Palsy from Stroke

The key distinguishing feature is forehead involvement: Bell's palsy causes complete unilateral facial weakness including the forehead, while stroke spares the forehead due to bilateral cortical innervation of upper facial muscles. 1, 2

Critical Clinical Distinctions

Forehead Function Test

• In Bell's palsy, patients cannot wrinkle their forehead or raise their eyebrow on the affected side because the peripheral facial nerve lesion affects all ipsilateral facial muscles 2, 3
• In stroke, forehead wrinkling is preserved because upper facial muscles receive bilateral cortical innervation, making this the single most important distinguishing feature 2
• Failure to test forehead function can lead to misdiagnosis and is a critical pitfall 1

Temporal Profile

• Bell's palsy develops rapidly over less than 72 hours with acute onset 4, 1, 2
• Stroke typically presents with sudden onset (seconds to minutes) rather than progressive worsening over hours 5
• Slow progression beyond 72 hours suggests an alternative diagnosis, not Bell's palsy 2

Associated Neurologic Findings

• Bell's palsy is isolated to the facial nerve with possible ipsilateral ear pain, hyperacusis, taste disturbance, and dry eye/mouth 1, 2
• Stroke presents with additional neurologic deficits such as limb weakness, sensory changes, speech difficulties, visual field defects, or altered consciousness 4
• Any involvement of other cranial nerves or limb weakness immediately excludes Bell's palsy 2, 3

Systematic Examination Approach

Facial Movement Assessment

• Test raising eyebrows (frontalis muscle) - this is the critical differentiating test 1, 2
• Assess tight eye closure (orbicularis oculi) 1
• Evaluate smiling and showing teeth (orbicularis oris) 1
• Check puffing out cheeks (buccinator) 1
• Observe for nasolabial fold flattening and mouth drooping 2, 6

Additional Examination Elements

• Evaluate taste on anterior two-thirds of tongue if equipment available 1
• Test corneal reflex (should be present bilaterally in Bell's palsy) 7
• Assess for hyperacusis (stapedius muscle involvement) 4, 2
• Check for other cranial nerve involvement to exclude stroke or other pathology 2, 3

Red Flags Requiring Imaging

Indications for Immediate Neuroimaging

• Any additional neurologic deficits beyond isolated facial weakness 2, 3
• Bilateral facial weakness (extremely rare in Bell's palsy) 2, 3
• Altered consciousness or encephalopathy 7
• Severe hypertension with acute presentation 7
• Isolated branch paralysis rather than complete hemifacial involvement 2
• History of head and neck cancer 4, 2

Imaging Modality

• MRI with and without contrast is the test of choice when imaging is indicated 1, 2
• Routine imaging is NOT recommended for typical Bell's palsy presentations 1, 2

Common Stroke Mimics

Bell's Palsy as a Stroke Mimic

• Bell's palsy accounts for 10% of pediatric stroke mimics 4
• In adults, 0.8% of ED patients diagnosed with Bell's palsy received an alternative diagnosis within 90 days, with stroke being the most common 8
• Risk factors for misdiagnosis include increasing age, diabetes, and black race 8

Rare Pontine Stroke Presentation

• Lacunar infarcts of the dorsal pons can rarely present as isolated facial palsy mimicking Bell's palsy 7
• These cases may show preserved corneal reflexes but have associated findings like severe hypertension, encephalopathy, or subtle brainstem signs 7
• When clinical presentation is atypical (severe hypertension, altered mental status, acute onset with vascular risk factors), pursue imaging even if facial palsy appears peripheral 7

Management Algorithm Based on Diagnosis

If Bell's Palsy is Confirmed

• Prescribe oral corticosteroids within 72 hours (prednisolone 50 mg daily for 10 days OR prednisone 60 mg daily for 5 days with 5-day taper) for patients ≥16 years 1, 2
• Implement immediate eye protection with lubricating drops, ointments, and nighttime taping/patching 1, 2
• Consider antiviral therapy in combination with steroids (not as monotherapy) 1
• Arrange follow-up at 3 months if incomplete recovery 1, 2

If Stroke is Suspected

• Activate stroke protocol immediately with urgent neuroimaging 4
• Time-sensitive thrombolysis consideration if within therapeutic window 4
• Comprehensive stroke workup including vascular imaging 4

Critical Pitfalls to Avoid

• Never assume facial palsy is Bell's palsy without testing forehead function - this is the most common diagnostic error 1, 2
• Do not delay imaging in patients with atypical features, vascular risk factors, or additional neurologic signs 2, 7, 8
• Avoid prescribing antiviral monotherapy, which is ineffective 1, 2
• Do not initiate steroids beyond 72 hours, as there is no evidence of benefit 1
• Never neglect eye protection in patients with incomplete eye closure, as corneal damage can occur rapidly 1, 2