What is the appropriate work‑up for a patient with suspected Bell’s palsy?

Work-up for Suspected Bell's Palsy

The work-up for suspected Bell's palsy is primarily clinical—perform a thorough history and physical examination to exclude alternative causes, but do NOT obtain routine laboratory tests or imaging studies. 1

Essential History Components

When evaluating a patient with acute unilateral facial weakness, document the following specific elements:

• Timing of symptom onset: Bell's palsy develops suddenly over less than 72 hours; gradual progression beyond 3 weeks suggests tumor, infection, or other pathology 1, 2
• Associated neurologic symptoms: Ask specifically about dizziness, dysphagia, diplopia, limb weakness, or sensory changes—any of these exclude Bell's palsy and indicate brainstem or central pathology 1, 3
• Viral prodrome: Document recent upper respiratory infection or viral illness 1
• Hyperacusis: Increased sensitivity to sound suggests facial nerve involvement proximal to the stapedius branch 1
• Taste disturbance: Altered taste on the anterior two-thirds of the tongue indicates involvement proximal to the chorda tympani 2
• Ear or facial pain: Ipsilateral pain around the ear is common in Bell's palsy 2
• Medical history: Specifically inquire about diabetes, hypertension, pregnancy, obesity, prior stroke, brain tumors, head/facial skin cancers, parotid tumors, or recent head trauma 1, 2

Critical Physical Examination Elements

The physical examination must systematically assess facial nerve function and exclude alternative diagnoses:

Facial Nerve Motor Function

• Forehead involvement is mandatory: Inability to wrinkle the forehead or raise the eyebrow on the affected side distinguishes peripheral (Bell's palsy) from central lesions (stroke) 2, 4
• Grade severity using House-Brackmann scale: Document whether paralysis is complete (grade 6) or incomplete (grades 2-5), as this predicts prognosis—incomplete paralysis has up to 94% complete recovery vs. 70% with complete paralysis 2, 4
• Test all facial movements systematically: Raising eyebrows, closing eyes tightly, smiling, showing teeth, puffing out cheeks, and pursing lips 2

Eye Examination

• Assess eye closure: Document lagophthalmos (incomplete eyelid closure) and measure the gap in millimeters 2, 4
• Check for corneal exposure signs: Redness, foreign body sensation, discharge, or dryness require immediate protective measures 2, 4
• Test Bell's phenomenon: The globe should turn upward with attempted eye closure—this protective reflex helps prevent corneal damage 2

Cranial Nerve Examination

• Examine ALL other cranial nerves: Involvement of cranial nerves other than CN VII excludes Bell's palsy and suggests brainstem pathology, cerebellopontine angle tumor, or systemic disease 1

Red Flags Requiring Imaging

• Forehead sparing: Suggests stroke, not Bell's palsy 3, 4
• Bilateral facial weakness: Consider Lyme disease, sarcoidosis, or Guillain-Barré syndrome 4
• Isolated branch paralysis: Suggests tumor or trauma 2
• Recurrent paralysis on the same side: Warrants MRI to exclude tumor 2
• Progressive weakness beyond 3 weeks: Indicates alternative diagnosis 2
• Presence of anomia or language disturbance: Indicates cortical involvement requiring urgent stroke evaluation 3

Laboratory Testing: NOT Recommended

Do not obtain routine laboratory tests in patients with typical Bell's palsy presentation. 1, 2 This is a strong recommendation against routine testing because:

• Laboratory tests delay treatment initiation beyond the critical 72-hour window 2
• No laboratory test confirms or excludes Bell's palsy 1
• Testing is only indicated when history or examination suggests specific alternative diagnoses (e.g., Lyme serology if endemic area with tick exposure, glucose testing if undiagnosed diabetes suspected) 1

Diagnostic Imaging: NOT Recommended

Do not routinely perform diagnostic imaging for patients with new-onset Bell's palsy. 1, 2 Imaging is reserved only for atypical presentations:

When to Order MRI (with and without contrast)

• Recurrent paralysis on the same side 2
• Isolated branch paralysis 2
• Other cranial nerve involvement 1, 2
• No sign of recovery after 3 months 2
• Progressive weakness beyond 3 weeks 2
• Bilateral facial weakness 4
• New or worsening neurologic findings at any point 2

Electrodiagnostic Testing: Limited Role

Do not perform electrodiagnostic testing in patients with incomplete facial paralysis. 1 The testing provides no actionable information in this group. 2

May offer electrodiagnostic testing to patients with complete facial paralysis. 1 However, this is optional, not mandatory:

• Testing is most reliable when performed 3-14 days after symptom onset (before 7 days or after 21 days yields unreliable results due to ongoing Wallerian degeneration) 2
• Greater than 10% nerve response amplitude compared to the unaffected side indicates excellent prognosis 2
• Less than 10% function carries up to 50% risk of incomplete recovery 2, 4

Common Pitfalls to Avoid

• Missing central causes: Failure to test forehead function leads to misdiagnosis of stroke as Bell's palsy 4
• Delaying treatment for unnecessary tests: Ordering routine labs or imaging delays corticosteroid initiation beyond the 72-hour therapeutic window 2
• Inadequate eye examination: Missing lagophthalmos risks permanent corneal damage 2, 4
• Incomplete cranial nerve examination: Other cranial nerve involvement excludes Bell's palsy but is easily missed without systematic testing 1
• Ignoring atypical features: Bilateral weakness, isolated branch paralysis, or gradual progression require imaging, not empiric treatment 2, 4

Summary Algorithm

1. Acute unilateral facial weakness with forehead involvement → Proceed with clinical diagnosis
2. Document timing (sudden onset <72 hours) and exclude red flags (other CN involvement, bilateral weakness, forehead sparing, anomia)
3. If typical Bell's palsy → No labs, no imaging, initiate treatment within 72 hours
4. If atypical features present → Order MRI with/without contrast before or concurrent with treatment
5. If complete paralysis → Consider electrodiagnostic testing at 3-14 days (optional)
6. All patients → Implement immediate eye protection if lagophthalmos present