Abstract
In patients with hemifacial spasm, stimulation of the zygomatic branch or the marginal mandibular branch of the facial nerve elicits abnormal muscle responses (AMRs) in the mentalis muscle or orbicularis oculi muscle respectively, although these muscles are normally innervated by the the marginal mandibular branch and zygomatic branch, respectively. The AMRs are specific for patients with hemifacial spasm and are called "exaggerated F waves". The F wave that is observed in the mentalis muscle following marginal mandibular branch stimulation is a small recurrent discharge, which antidromically propagates to the facial motor nucleus and returns orthodromically down the same axon. The F wave is enhanced on the spasm side, which means that the excitability of the facial motor nucleus increases in patients with hemifacial spasm. This concept is important for considering the clinical course of patients with hemifacial spasm before and after microvascular decompression surgery.
