Reduction in intraoperative lateral spread response as a prognostic neurophysiological parameter in microvascular decompression for hemifacial spasm: A retrospective cohort study

Abstract

Hemifacial spasm (HFS) is caused by vascular compression of the facial nerve at its root exit zone, and microvascular decompression (MVD) remains the gold standard treatment, although intraoperative confirmation of adequate decompression is challenging. The lateral spread response (LSR), an abnormal facial muscle response elicited by nerve stimulation, has been used to guide intraoperative decision-making, but its predictive accuracy remains debated. The aim of this study was to identify an optimal LSR diminution threshold as a dependable prognostic indicator for surgical success. A retrospective observational study was conducted on 34 patients who underwent MVD for primary HFS between January 2023 and December 2025. Intraoperative delta LSR, defined as the change in LSR activation threshold from baseline to post-decompression, was analyzed using receiver operating characteristic (ROC) analysis. Firth penalized-likelihood logistic regression was performed as an exploratory sensitivity analysis. Complete spasm resolution at six months was achieved in 29 patients (85.3%). A delta LSR cut-off of ≥15.0 mA discriminated complete resolution from partial improvement with moderate to good discrimination (area under the curve: 0.793; 95% confidence interval (95%CI): 0.614–0.936), corresponding to a 100.0% success rate above this threshold versus 70.6% below it (Fisher’s exact p=0.044). This association persisted in direction and magnitude after adjustment for age, sex, and symptom onset duration using Firth’s method (adjusted odds ratio: 1.18 per 1 mA increase; 95%CI: 0.96–1.45). These findings support intraoperative delta LSR, particularly a threshold of ≥15.0 mA, as an adjunct for guiding MVD in HFS. Nevertheless, validation in larger, prospectively followed, multicenter cohorts is warranted before delta LSR is adopted for intraoperative decision-making.