Abnormal evoked EMG and blink reflex responses in patients with hemifacial spasm (HFS)

Abnormal evoked EMG and blink reflex responses have been observed on the affected side in patients with HFS. These characteristic responses were used as methods of preoperative differential diagnosis, and the disappearance of these abnormal responses during intraoperative monitoring was assessed as confirmation of nerve decompression. The subjects were 30 patients with a diagnosis of HFS. Three responses were evaluated: 1) the orbicularis oris muscle (OR) response to stimulation of the orbicularis oculi muscle branch (OB), OB → OR; 2) the orbicularis oculi muscle (OC) response to stimulation of the marginal mandibular branch (MB), MB → OC; and 3) the (OR) response to stimulation of the supraorbital nerve (SO), SO → OR. The facial nerve in the root exit zone was compressed by a vessel in all 21 patients diagnosed as typical HFS who had abnormal responses, and OB → OR was always detected. The MB → OC and SO → OR detection rates were low (50% and 25%, respectively) when the interval since the onset of HFS was less than 3 years, but increased to 78% and 67%, respectively, when it was 3 to 5 years, and all three abnormal responses were always detected when the interval was more than 5 years. In 17 of the patients these responses began to change and eventually disappeared before decompression of the facial nerve, and in 2 patients they persisted even after decompression. Abnormal responses disappeared at the time of decompression in only 2 patients, and their HFS was completely cured postoperatively. These findings confirmed that disappearance of abnormal responses is not a very useful guide for facial nerve decompression. When abnormal responses were observed in patients with HFS and a cerebello-pontine angle tumor, it indicated a possible compression vessel in the root exit zone of the facial nerve.