Bell's palsy is a paralysis of cranial nerve VII (the facial nerve) resulting in inability to control facial muscles on the affected side. Several conditions can cause a facial paralysis, e.g., brain tumor, stroke, and Lyme disease. However, if no specific cause can be identified, the condition is known as Bell's palsy. Bell's palsy is defined as an idiopathic unilateral facial nerve paralysis, usually self-limiting. The trademark is rapid onset of partial or complete palsy, usually in a single day.
Bell’s palsy is largely a diagnosis of exclusion, but certain features in the history and physical examination help distinguish it from facial paralysis due to other conditions: eg, abrupt onset with complete, unilateral facial weakness at 24 to 72 hours, and, on the affected side, numbness or pain around the ear, a reduction in taste, and hypersensitivity to sounds. Corticosteroids and antivirals given within 10 days of onset have been shown to help. But Bell palsy resolves spontaneously without treatment in most patients within 6 months.
Brighton Collaboration definition: Rath B, et al. Bells palsy: Case definitions and guidelines for collection, analysis, and presentation of immunization safety data. (Manuscript)