Hemimasticatory spasm in hemifacial atrophy: diagnostic and therapeutic aspects in two patients.

We report two cases of hemimasticatory spasm in association with progressive hemifacial atrophy. On the basis of neurophysiological and magnetic resonance imaging assessments, a peripheral irritation of the trigeminal nerve--probably due to entrapment of the motor branches in the infratemporal fossa--is suggested as the cause of the involuntary movement. Local injections of botulinum toxin type A into the masticatory muscles proved to be a successful treatment in both patients.