What is the appropriate work‑up for a patient with new unilateral lower‑face weakness suggestive of Bell’s palsy?

Bell's Palsy Work-Up

For a patient with new unilateral lower-face weakness suggestive of Bell's palsy, perform a focused history and physical examination to exclude alternative causes—then do NOT order routine laboratory tests or imaging for typical presentations. 1, 2

Initial Clinical Assessment

History elements to document:

• Onset timing: Acute unilateral facial weakness developing over ≤72 hours is characteristic; gradual progression beyond 3 weeks suggests tumor or infection 2, 3
• Associated symptoms: Presence of dizziness, dysphagia, diplopia, limb weakness, or sensory changes excludes Bell's palsy and indicates central/brainstem pathology 2
• Viral prodrome: Recent upper respiratory infection or viral illness is commonly reported 2
• Hyperacusis: Increased sound sensitivity indicates proximal facial nerve involvement 2
• Medical history: Diabetes, hypertension, pregnancy, obesity, prior stroke, head/neck cancers, parotid tumors, or recent trauma 2

Physical examination must include:

• Forehead function testing: Inability to wrinkle forehead or raise eyebrow on affected side confirms peripheral lesion; forehead sparing indicates stroke 2, 4
• Complete cranial nerve examination: Any other cranial nerve involvement excludes Bell's palsy and mandates imaging 1, 2
• Severity grading: Use House-Brackmann scale (Grade 1 = normal to Grade 6 = complete paralysis) to document baseline 2, 4
• Eye closure assessment: Test ability to close eyelid completely; incomplete closure requires immediate protective measures 2, 4
• Systematic facial movement testing: Assess eyebrow raising, eye closing, smiling, and cheek puffing 2

Diagnostic Testing: What NOT to Order

Routine laboratory testing is NOT recommended for typical Bell's palsy presentations—ordering labs delays treatment beyond the critical 72-hour window without improving outcomes. 1, 2 Laboratory investigations are only indicated when history or examination raises suspicion for specific alternative diagnoses (e.g., Lyme serology in endemic areas, glucose testing for undiagnosed diabetes). 2

Routine imaging is NOT recommended for new-onset Bell's palsy with typical features. 1, 2 This is a strong recommendation based on observational studies showing no benefit and potential harm from treatment delays. 1

Electrodiagnostic testing is NOT performed in patients with incomplete facial paralysis because it provides no actionable information. 1, 2 Optional testing may be offered only to patients with complete paralysis, ideally 3–14 days after symptom onset. 2

Red Flags Requiring MRI and Specialist Referral

Order MRI with and without contrast if ANY of these features are present:

• Recurrent paralysis on the same side 1, 2
• Isolated branch paralysis (e.g., only lower face affected) 1, 2
• Other cranial nerve involvement 1, 2, 4
• Bilateral facial weakness 2, 4
• Forehead sparing (suggests stroke) 2, 4
• Progressive weakness beyond 3 weeks 2
• No recovery after 3 months 1, 2
• New or worsening neurologic findings at any point 2, 5

The presence of any red flag fundamentally changes the diagnosis from Bell's palsy to an alternative etiology requiring imaging and specialist evaluation. 2

Prognostic Assessment at Initial Visit

Incomplete paralysis (any visible facial movement) predicts up to 94% complete recovery and indicates excellent prognosis. 2, 4 These patients do not require electrodiagnostic testing. 1, 2

Complete paralysis (no visible movement) carries up to 50% risk of incomplete recovery. 4 Consider offering electrodiagnostic testing 3–14 days post-onset; >10% nerve response amplitude compared to unaffected side indicates excellent prognosis. 2

Common Pitfalls to Avoid

• Missing forehead involvement: Failing to test forehead function leads to misdiagnosis of stroke as Bell's palsy 2, 4
• Ordering unnecessary tests: Routine labs and imaging for typical presentations increase costs, delay treatment, and provide no benefit 1, 2, 5
• Inadequate cranial nerve examination: Missing involvement of other cranial nerves delays diagnosis of brainstem pathology or tumor 1, 2
• Delaying treatment for test results: The 72-hour treatment window for corticosteroids is absolute; do not delay therapy to obtain unnecessary diagnostic studies 2, 5