ELECTROPHYSIOLOGICAL DETERMINATION OF THE SITE INVOLVED IN GENERATINGABNORMAL MUSCLE RESPONSES IN HEMIFACIAL SPASM

In patients with hemifacial spasm (HFS), abnormal muscle responses due to abnormal cross-transmission are observed in facial muscles. Howeve r, the site in the facial nerve responsible for the cross-transmission remains a matter of controversy. We have developed a model in which b y considering the electrophysiological parameters involved in producin g the abnormal muscle response, we can determine the site of the abnor mal cross-transmission within the facial nerve. This model was applied to HFS patients with three different etiologies: idiopathic, post-Bel l's palsy, and post-XII-VII anastomosis. Our data show that: in idiopa thic HFS, the cross-transmission may occur in the facial nerve at the level of the pontocerebellar angle; in post-Bell's palsy, it is inside the petrous bone; and in XII-VII anastomosis, it must be in the extra cranial part of the facial nerve. The possible mechanisms for this cro ss talk are discussed in terms of ephaptic transmission or of a centra l hyperexcitability in the facial motor nucleus. (C) 1998 John Wiley & Sons, Inc.