Objective: The lateral spread response (LSR) is an aberrant electrophysiological response in which a stimulus on one branch of the facial nerve spills over to other branches of the nerve, which can be captured by electrodes near each branch. The authors performed this study to evaluate the prognostic value of the follow-up LSR with a sufficient time interval from intraoperative LSR (IO-LSR) after microvascular decompression (MVD) for hemifacial spasm (HFS), excluding the interference of various intraoperative situations.
Methods: A total of 247 patients treated with MVD for HFS between June 2011 and March 2019 were enrolled in this study. The IO-LSR was routinely evaluated in all patients. The LSR was checked again on postoperative day (POD) 2 after surgery (POD2-LSR). A total of 228 patients (92.3%) were considered cured at the last clinical follow-up.
Results: The IO-LSR disappeared in 189 patients (76.5%), and among them, 181 patients (95.8%) were cured 1 year after surgery. The POD2-LSR disappeared in 193 patients (78.1%), and 185 patients (95.9%) among them were cured. Among the 189 patients in which the IO-LSR disappeared, the POD2-LSR reappeared in 26 patients (13.8%). In contrast, the POD2-LSR disappeared in 30 (51.7%) of 58 patients for whom the IO-LSR continued at the end of surgery. When classified into groups according to the status of the IO-LSR and POD2-LSR, in the group of patients in whom both LSRs disappeared, the cure rate was 98.2%, which was significantly higher than that of the other 3 groups (p < 0.05, Cochran-Armitage trend test). The use of both LSRs was found to be significantly associated with better predictability (p < 0.05, McNemar's test).
Conclusions: Postoperative follow-up LSR examination may be beneficial in predicting clinical outcomes after MVD for HFS, especially when considered together with IO-LSR.
Keywords: hemifacial spasm; intraoperative neurophysiologic monitoring; lateral spread response; microvascular decompression; neurovascular cross compression; pain.