What is the recommended work‑up for a patient with acute unilateral peripheral facial weakness suggestive of Bell’s palsy?

Bell's Palsy Work-Up

For typical Bell's palsy presentations, NO laboratory testing or imaging is required—diagnosis is clinical based on history and physical examination alone. 1

Clinical Diagnosis

Bell's palsy is diagnosed when a patient presents with acute unilateral facial weakness involving the forehead that develops over less than 72 hours, with no identifiable alternative cause. 1, 2 This is a diagnosis of exclusion requiring careful elimination of other etiologies through focused history and examination. 1, 2

Essential History Elements

• Onset timing: Confirm symptom development occurred within 72 hours—this rapid onset is cardinal for Bell's palsy. 2, 3
• Associated symptoms: Ask specifically about ipsilateral ear or facial pain, taste disturbance on the anterior two-thirds of the tongue, hyperacusis (increased sound sensitivity), and dry eye or mouth. 1, 3
• Exclude alternative causes: Specifically inquire about recent trauma (temporal bone fracture), tick exposure (Lyme disease), vesicular rash (herpes zoster/Ramsay Hunt), history of cancer, and other neurologic symptoms suggesting stroke. 1, 2, 4

Physical Examination Requirements

Facial nerve assessment:

• Test all facial movements systematically: raise eyebrows, close eyes tightly, smile, puff out cheeks. 1, 3
• Forehead involvement is mandatory—forehead sparing indicates central (stroke) rather than peripheral pathology. 1, 2
• Grade severity using House-Brackmann scale (Grade 1 = normal to Grade 6 = total paralysis). 1, 3
• Assess eye closure carefully to determine corneal exposure risk. 1

Critical exclusionary examination:

• Test ALL other cranial nerves (V, VI, VIII, IX, X, XI, XII)—any additional cranial nerve involvement excludes Bell's palsy and mandates imaging. 2, 4
• Perform otoscopic examination to exclude middle ear pathology and look for vesicles suggesting herpes zoster. 5
• Check for parotid masses that could indicate tumor. 5

When Laboratory Testing IS Indicated

Routine labs are NOT recommended for typical Bell's palsy. 1 However, consider targeted testing only when history suggests specific alternative diagnoses:

• Lyme serology: Only if patient has tick exposure history or lives in endemic area. 4, 6
• Glucose/HbA1c: Only if diabetes is not already diagnosed and risk factors are present. 7, 6

When Imaging IS Required

Routine imaging is NOT indicated for typical Bell's palsy presentations. 1, 2 Order MRI with and without contrast (the gold standard) ONLY for these red flags: 1, 2

• Bilateral facial weakness (suggests Lyme disease, sarcoidosis, or Guillain-Barré syndrome) 2, 4
• Isolated branch paralysis (not complete hemifacial involvement) 1
• Recurrent paralysis on the same side 1
• Other cranial nerve involvement 2, 4
• Progressive weakness beyond 72 hours 1
• No recovery after 3 months 1
• History of head and neck cancer 3

Electrodiagnostic Testing

• NOT recommended for incomplete facial paralysis 1
• May be offered for complete facial paralysis, performed 3-14 days post-onset (testing before 7 days or after 14-21 days is unreliable due to ongoing Wallerian degeneration) 1
• Electroneurography (ENoG) showing >10% nerve response amplitude predicts excellent prognosis; <10% function carries up to 50% risk of incomplete recovery 1

Common Pitfalls to Avoid

• Ordering unnecessary tests delays treatment—corticosteroids must be initiated within 72 hours for maximum benefit. 1, 8
• Missing forehead examination—failure to confirm forehead involvement can lead to misdiagnosis of stroke as Bell's palsy. 1
• Overlooking other cranial nerve deficits—this excludes Bell's palsy and indicates serious pathology requiring urgent imaging. 2, 4
• Assuming bilateral weakness is Bell's palsy—this is rare and mandates investigation for systemic causes. 2, 4

Immediate Management After Diagnosis

Once Bell's palsy is clinically diagnosed:

• Initiate oral corticosteroids immediately (prednisolone 50 mg daily for 10 days OR prednisone 60 mg daily for 5 days with 5-day taper) within 72 hours of symptom onset. 1, 7
• Implement eye protection for any degree of impaired eye closure: frequent lubricating drops during the day, ophthalmic ointment at night, eye taping if needed, and sunglasses outdoors. 1, 3
• Consider adding antiviral therapy (valacyclovir 1 g three times daily for 7 days OR acyclovir 400 mg five times daily for 10 days) to corticosteroids—never use antivirals alone. 1, 7