Hemifacial spasm and involuntary facial movements.

Hemifacial spasm (HFS) is characterized by tonic and clonic contractions of the muscles innervated by the ipsilateral facial nerve. It is important to distinguish this from other causes of facial spasms, such as psychogenic facial spasm, facial tic, facial myokymia, blepharospasm, and tardive dyskinesia. Magnetic resonance imaging and angiography studies frequently demonstrate vascular compression of the root exit zone of the facial nerve. Importantly, an underlying space-occupying lesion needs to be excluded in patients with associated atypical features such as facial numbness and weakness. Botulinum toxin injection to the facial muscles is an effective treatment for HFS, with few disabling side-effects.