Effect of botulinum neurotoxin treatment in the lateral spread monitoring of microvascular decompression for hemifacial spasm

Introduction: Botulinum neurotoxin (BtNtx) treatment for hemifacial spasm (HFS) prior to microvascular decompression (MVD) is hypothesized to be a factor in the variability of intraoperative neurophysiological monitoring (IONM) during this procedure. Methods: We analyzed 282 MVDs performed at the University of Pittsburgh Medical Center between January 1, 2000 and December 31, 2007. We retrospectively compared the lateral spread response (LSR) in the mentalis muscle when stimulus‐triggered electromyography (EMG) was elicited from the facial nerve. Previous BtNtx treatment was the grouping factor. Results: Baseline LSR amplitudes during MVD (prior BtNtx: mean = 341.47 μV; no BtNtx: mean = 241.81 μV) were significantly different between groups (df = 1,281; t = −2.463; P = 0.014). Comparisons of latency and current threshold at baseline, as well as HFS disappearance or LSR persistence after the procedure, did not achieve statistical significance. Conclusions: HFS patients treated with BtNtx prior to MVD demonstrated higher LSR baseline amplitudes during IONM. This could be related to muscle poly‐reinnervation after recovery from repeated BtNtx use. Muscle Nerve, 2011