Facial paralysis and Bell's palsy: a protocol for differential diagnosis.

In the past, most cases of facial paralysis have been erroneously labeled Bell's palsy. Bell's palsy has been synonymous with and defined as idiopathic facial paralysis affecting only the facial nerve within the confines of the temporal bone. In the last ten years, Bell's palsy has been redefined as viral polyneuritis, probably caused by herpes simplex reactivation, and its diagnosis is no longer reached by exclusion. This article discusses the signs, symptoms, and testing necessary to confidently and accurately differentiate Bell's palsy from other forms of facial paralysis. The nonspecificity of topographic diagnosis is discussed and statistical analysis of factors affecting prognosis are included.