Treatment with botulinum toxin improves the hyperexcitability of the facial motoneuron in patients with hemifacial spasm.

Botulinum toxin type A (BTX) injection into the orbicularis oculi muscle is an effective treatment for patients with hemifacial spasm (HFS). The objectives of this study were to investigate the effect of this treatment on HFS, in particular the associated hyperexcitability of the facial motor nucleus, and to discuss the potential mechanism of HFS. F waves in the mentalis muscle were examined before, 2 and 6 weeks after the BTX treatment of only the orbicularis oculi muscle in ten patients with HFS.