Objective:To study the clinical value of monitoring facial electromyographic(EMG) responses during microvascular decompression for hemifacial spasm(HFS).Methods:Facial EMG responses were monitored pre-operatively and post-operatively and during microvascular decompression of 68 patients with HFS.The stimulating electrodes were inserted over the mentalis muscle

while evoked facial EMG responses were monitored in orbicularis oculi.Results:Abnormal EMG responses(MD-OC)were recorded pre-operatively in all 68 patients.In 60 patients

the MD-OC disappeared at different stages of procedure from dural opening through vascular mobilization.Those patients were free of spasm at 6-month follow-up.7 out of 8 patients in whom the MD-OC was recorded even at the end of operation were also clinically cured at the 6-month follow-up visit

whereas spasm persisted in 1 patient.Conclusion:This study demonstrates monitoring facial EMG responses is useful in estimating efficacy of decompression and helpful in predicting prognosis in hemifacial spasm.