The potential value of the disappearance of the lateral spread response during microvascular decompression for predicting the clinical outcome of hemifacial spasms: A prospective study

BACKGROUND: Hemifacial 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. OBJECTIVE: To clarify the effectiveness of intraoperative electromyogram during microvascular decompression (MVD) for HFS. METHODS: Two 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). CONCLUSION: The 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.