The utility of "low current" stimulation threshold of intraoperative electromyography monitoring in predicting facial nerve function outcome after vestibular schwannoma surgery: a prospective cohort study of 103 large tumors.

To investigate the predictive utility of stimulation threshold (ST) of intraoperative electromyography monitoring for facial nerve (FN) outcomes among vestibular schwannoma (VS) patients postoperatively. The authors enrolled 103 unilateral VS patients who underwent surgical resection into a prospective cohort observational study from January 2013 to April 2015 in our hospital. ST values were used to categorize 81 patients into the "low current" (ST ≤ 0.05 mA) group and 22 patients into the control (ST > 0.05 mA) group. The FN function outcomes were summarized and correlated with these two groups at 1, 3, 6, and 12 months after surgery. Binary regression analysis revealed that the percentage of "good" FN outcome, defined by House-Brackmann (HB) classification of facial function (I-II), in the "low current" group was significantly higher than that of the control group (42.0 vs. 4.5% at 1 month, P = 0.015; 64.2 vs. 31.8% at 3 months, P = 0.024; 72.8 vs. 40.9% at 6 months, P = 0.021; 84.0 vs. 45.5% at 12 months, P = 0.002). Ordinal regression analysis showed that the distribution of HB scores was shifted in a favorable direction in the "low current" group at 1, 3, 6, and 12 months postoperatively. For patients with HB IV at the first month postoperative period, the recovery rate of the "low current" group was significantly higher than that of control group (P = 0.003). "Low current" can predict FN function outcomes better and has faster recovery rates than that of the control group.