• Chang-Hyun Kim, Doo-Sik Kong, Jeong Ah Lee, and Kwan Park.
• 1Department of Neurosurgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
• Neurosurgery. 2020 Oct 12; 67 (6): 1581-1588.

BackgroundHemifacial spasm (HFS) is a benign, chronic, involuntary movement of the muscles involved in facial expressions that typically begins in the orbicularis oculi and spreads to the other expression muscles over several years.ObjectiveTo clarify the effectiveness of intraoperative electromyogram during microvascular decompression (MVD) for HFS.MethodsTwo hundred ninety-nine consecutive patients with HFS underwent continuous intraoperative monitoring during MVD. The patients were divided into 2 groups based on whether the lateral spread response (LSR) disappeared before or after decompression RESULTS:: In 276 of 299 patients (92.3%), the LSR was observed during intraoperative facial electromyogram monitoring. The mean follow-up period was 17.9 months (range, 12-27 months). Three patients in whom the LSR persisted despite decompression were not included in this study. In 183 of the 273 patients (67%), the LSR disappeared after decompression (group A); in the remaining 90 (33%), the LSR disappeared at dural opening or after drainage of the cerebrospinal fluid before decompression (group B). At the postoperative 3-month and 2-year follow-up visits, there were significant differences in the clinical outcomes between the 2 groups (P < .05).ConclusionThe disappearance of the LSR before and after MVD may predict clinical outcomes. This must be considered together with the disappearance or persistence of LSR after decompression as a prognostic factor for HFS after MVD.

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