[Neurophysiological study on hemifacial spasm--the abnormality and origin of the electromyographic response to stimulation of the facial nerve].

Electromyographic responses (MD-OC) of the orbicularis oculi muscle to stimulation of ipsilateral marginal mandibular branch of the facial nerve were recorded in 20 patients with hemifacial spasm, pre-, post-operatively and during operations to relieve it by microvascular decompression, and the abnormal features and origin of the MD-OC were investigated. On the affected side, the MD-OC were recorded in pre- and during operative state, and disappeared with disappearance of hemifacial spasm after microvascular decompression, while no response was recorded in pre-, during and post-operative state on the healthy side. In 17 patients, the MD-OC was recorded continuously during operation. In all cases except for one case in whom the MD-OC was recorded even the end of operation, the MD-OC disappeared on several stage of procedure from dural opening through vascular mobilization. The compound nerve action potential (MD-VII) to stimulation of the marginal mandibular branch was recorded from the facial nerve near its root entry zone after exposure of the intracranial portion. There were two patterns in the records, i.e., one group consisting of early component and the other consisting of early and late component. The MD-VII was only consisted of the early component in 12 cases in whom the MD-OC have already disappeared, and was consisted of the early and late component in 5 cases in whom the MD-OC still recorded. And in 2 cases of the later, the late component disappeared simultaneously with disappearance of the MD-OC during vascular mobilization.(ABSTRACT TRUNCATED AT 250 WORDS)