Describe the clinical evaluation.
Bell palsy is a clinical diagnosis of exclusion.
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.
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. 
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).
List diagnostic studies.
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.
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