What is the treatment approach for differentiating between Bell's palsy and Horner's syndrome?

Differentiating Bell's Palsy from Horner's Syndrome

Bell's palsy and Horner's syndrome are fundamentally different conditions that are easily distinguished by physical examination: Bell's palsy causes unilateral facial weakness involving the forehead with inability to close the eye, while Horner's syndrome presents with ptosis, miosis, and anhidrosis without any facial weakness.

Key Clinical Distinctions

Bell's Palsy Presentation

• Forehead involvement is the critical distinguishing feature - patients cannot wrinkle their forehead or raise their eyebrow on the affected side, distinguishing it from central (stroke) causes of facial weakness 1, 2
• Acute onset of unilateral facial weakness developing over less than 72 hours 1
• Complete inability to close the eye on the affected side (lagophthalmos) 2
• Drooping of the corner of the mouth with inability to smile symmetrically 2
• May have ipsilateral ear pain, altered taste on anterior two-thirds of tongue, hyperacusis, or dry eye 1, 2

Horner's Syndrome Presentation

• No facial weakness whatsoever - this is the key differentiator
• Ptosis (drooping eyelid) but the patient can still voluntarily close the eye completely
• Miosis (constricted pupil) on the affected side
• Anhidrosis (decreased sweating) on the affected side of the face
• Facial strength is completely normal - patient can raise eyebrows, close eyes, and smile symmetrically

Physical Examination Algorithm

Step 1: Test Forehead Function

• Ask patient to raise eyebrows and wrinkle forehead 2
• Bell's palsy: Cannot raise eyebrow or wrinkle forehead on affected side
• Horner's syndrome: Normal forehead movement bilaterally

Step 2: Test Eye Closure

• Ask patient to close eyes tightly 2
• Bell's palsy: Cannot close eye on affected side, with visible gap and Bell's phenomenon (eye rolls upward) 2
• Horner's syndrome: Can close eye completely, though upper lid may appear slightly drooped at rest

Step 3: Examine Pupils

• Bell's palsy: Pupils are equal and reactive
• Horner's syndrome: Affected pupil is smaller (miosis) and may have delayed dilation in darkness

Step 4: Test Facial Strength

• Ask patient to smile, puff out cheeks, show teeth 2
• Bell's palsy: Weakness of lower face with drooping mouth corner
• Horner's syndrome: Completely normal facial strength

Red Flags Suggesting Alternative Diagnosis

• Bilateral facial weakness suggests something other than Bell's palsy 1, 2
• Isolated branch paralysis (e.g., only lower face affected) is atypical for Bell's palsy 2
• Other cranial nerve involvement suggests alternative diagnosis 2
• Gradual onset over weeks suggests tumor rather than Bell's palsy 1

Diagnostic Testing

• No routine laboratory testing or imaging is needed for typical Bell's palsy 1, 2, 3
• MRI with and without contrast is indicated only for atypical presentations, no recovery after 3 months, or worsening symptoms 2, 3

Critical Management Difference

Bell's Palsy Treatment

• Prescribe oral corticosteroids within 72 hours of symptom onset for patients 16 years and older: prednisolone 50 mg daily for 10 days OR prednisone 60 mg daily for 5 days followed by 5-day taper 1, 2, 3
• Implement immediate eye protection with lubricating drops, ointments at night, and eye taping to prevent corneal damage 1, 2, 3
• Do not prescribe antiviral therapy alone 1, 3

Horner's Syndrome Management

• Requires urgent workup to identify underlying cause (carotid dissection, lung tumor, brainstem lesion)
• No role for corticosteroids
• Imaging of the entire sympathetic pathway from hypothalamus to eye is essential

Common Pitfall to Avoid

The most critical error is confusing the ptosis of Horner's syndrome with the lagophthalmos (inability to close eye) of Bell's palsy - these are opposite problems. In Horner's syndrome, the eyelid droops but closes completely; in Bell's palsy, the eyelid cannot close at all. Testing voluntary eye closure immediately distinguishes these conditions 2.