The value of abnormal muscle response monitoring during microvascular decompression surgery for hemifacial spasm

Objective Abnormal muscle response(AMR) to the electrical stimulation of a branch of facial nerve is a specific electrophysiological feature of primary hemifacial spasm ( HFS ).Although the correlation between intraoperative AMR findings and postoperative results in patients with HFS has been investigated before,the AMR monitoring has not been employed widely during the microvascular decompression(MVD) surgery.The aim of this study was to evaluate the value of AMR monitoring during MVD,and the correlation between the AMR changes and the clinical outcome.Method This study included 241 cases of MVD.Intraoperative AMR monitoring was performed for each subject.The patients were divided into two groups based on whether the AMR wave disappeared or not following decompression of the facial nerve.Results The AMR disappeared after MVD in 175 patients.Among these 175 patients,165 (94.3％ ) patients were relieved from HFS 1 week after HFS.Out of the 66 patients in whom the AMR persisted after MVD,52 (78.8％ ) patients were relieved.The correlation between intraoperative AMR abolition and HFS relief was statistically significant ( P ＜ 0.05 ).Conclusions Intraoperative AMR monitoring is an effective assistant for a successful MVD for the patient with HFS.It may be helpful in predicting outcomes in short term and identifying offending vessels,so it should be monitored routinely during MVD. Key words: Abnormal muscle response ;  Hemifacial spasm ;  Microvascular decompression ;