• Miguel E Habeych, Aalap C Shah, Tara N Nikonow, Jeffrey R Balzer, Donald J Crammond, Parthasarathy D Thirumala, Amin Kassam, and Michael Horowitz.
• Center for Clinical Neurophysiology Department Neurological Surgery, University of Pittsburgh, UPMC Presbyterian, Pittsburgh, Pennsylvania 15213, USA. habeychme@upmc.edu
• Muscle Nerve. 2011 Oct 1; 44 (4): 518-24.

IntroductionBotulinum 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.MethodsWe 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.ResultsBaseline 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.ConclusionsHFS 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.Copyright © 2011 Wiley Periodicals, Inc.

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