Optimal method for reliable lateral spread response monitoring during microvascular decompression surgery for hemifacial spasm

Abstract

Abstract Objective Lateral spread response (LSR) is the key electrophysiological sign for successful decompression of conflict vessel at microvascular decompression (MVD) surgery for hemifacial spasm (HFS). But monitoring methods and interpretation of LSR is still unclear thus cause misinterpretation that results unwanted outcome. We suggest the optimal method to monitor LSR. Methods We prospectively collected data from patients undergoing MVD for HFS. Basic demographics, clinical characteristics and outcome were obtained. To find optimal range of stimulation to achieve effective LSR, we escalated stimulation intensity by 1mA stepwise. Then we compared findings of abnormal muscle response between optimal range and high intensity stimulation (30mA). Results As stimulation intensity increases, the latency to detect LSR was shortened. High intensity stimulation caused artifact that mimic the wave of LSR. Those artifacts were observed even after decompression thus interfere interpretation of disappearance of LSR. We found the LSR detected at latency below 9.6msec would be the lateral spreading artifact (LSA) rather than true LSR. Conclusion To avoid false positive LSR from LSA, we should stepwise increase stimulation intensity and not to surpass the intensity that cause LSR latency below 10msec.