Diagnostics

Bell palsy is a clinical diagnosis of exclusion.

• Medical history

  • Ask about symptom onset and duration (e.g., acute vs. progressive).

  • Assess for possible secondary causes, e.g., stroke, tumors, recent infections, and exposure from outdoor trips.

• Physical examination

  • Evaluate for facial asymmetry at rest.

  • Ask the patient to perform facial movements.

    • Assess for asymmetries and facial muscle strength.

    • Differentiate between motor signs in central and peripheral facial palsy.

  • Perform a complete neurological examination: Look for focal neurological signs.

  • Evaluate for signs indicative of a secondary cause, e.g., shingles , herpes zoster oticus , erythema migrans , tick bites, signs of trauma.

Typical features of Bell palsy include acute (< 72 hours), nonprogressive, unilateral peripheral facial nerve paralysis, with no identified cause after thorough clinical evaluation. [9]

When an acute central cause is suspected (e.g., other acute focal neurological symptoms are present), evaluate for ischemic stroke. Consider a tumor in patients with gradual onset, or slowly progressing neurological symptoms (e.g., change in mental status, involvement of select branches of the facial nerve and/or other cranial nerves, or other subacute focal neurological deficits).

Diagnostic studies are not routinely needed for acute unilateral facial nerve palsy unless a secondary cause is suspected (see “Etiology”) based on atypical symptoms and/or abnormal physical examination findings (See “Clinical features” and “Clinical evaluation”).

• Laboratory studies: Consider for select infectious causes.

  • VZV

  • Lyme disease

• Neuroimaging should be performed if neoplastic, vascular, or traumatic causes are suspected

Up to 25% of acute facial nerve palsy cases may be attributed to Lyme disease in highly endemic areas