Hemifacial spasm is an involuntary dyskinetic (not dystonic) movement disorder consisting of painless contractions of muscles on one side of the face, sometimes triggered by eating or speaking, and exacerbated by fatigue or emotion. The movements give a twitching appearance to the eye or side of the mouth, sometimes described as a pulling sensation. Patients often find this embarrassing because it attracts the attention of others. The movements may continue during sleep. Paradoxical elevation of the eyebrow as orbicularis oris contracts and the eye closes may be seen (Babinski’s "other sign"). Very rarely, movements may be bilateral.
Hemifacial spasm may be idiopathic, or associated with neurovascular compression of the facial (VII) nerve, usually at the root entry zone, often by a tortuous anterior or posterior inferior cerebellar artery. Other causes include intrapontine lesions (e.g., demyelination), following a Bell’s palsy, and mass lesions (tumor, arteriovenous malformation) located anywhere from the facial nucleus to the stylomastoid foramen. Very rarely, contralateral (false-localizing ) posterior fossa lesions have been associated with hemifacial spasm, suggesting that kinking or distortion of the nerve, rather than direct compression, may be of pathogenetic importance.
Structural lesions may be amenable to surgical resection. For idiopathic hemifacial spasm, or patients declining surgery, botulinum toxin injections are the treatment of choice.
Evidente VGH, Adler Ch H. Hemifacial spasm and other craniofacial movement disorders. Mayo Clinic Proceedings 1998; 73: 67-71