Correlating postoperative muscle and long-term functional outcomes with intraoperative muscle motor evoked potential changes in patients with benign intramedullary spinal cord tumors

Abstract

Background

We aimed to determine the diagnostic accuracy of intraoperative muscle motor evoked potentials (mMEPs) in predicting postoperative motor deficits in individual muscles of patients with benign intramedullary spinal cord tumors (IMSCTs), and to correlate them with long-term functional outcome.

Methods

A retrospective study of patients operated for benign IMSCTs from 2009 to 2021 was performed. Sixty-nine patients in whom baseline mMEP recordings were obtained from at least one muscle were included for analysis. A persistent drop of the baseline mMEP by ≥ 50% from baseline was considered significant.

Results

The mean age of the patients was 33.2 ± 15.8 years and 47 (68.1%) of them were male. The most common tumor was ependymoma (56.5%). Baseline mMEPs were obtained in 400/1011 muscles that were monitored. Postoperative worsening of motor power was noted in 109/400 (27.3%) muscles with baseline mMEP recordings compared to 213/611 (34.9%) muscles with no baseline recordings (p = 0.01). Patients who had deterioration of mMEPs had a significantly higher rate of worsening of muscle power postoperatively compared to those who had no deterioration of mMEPs (100% vs. 30.2%, p < 0.001). The sensitivity of mMEPs in predicting postoperative motor function in monitored muscles was 53.1% (95% CI 43.5–62.6), specificity was 97.9% (95% CI 95.5–99.2), PPV was 90.9% (95% CI 81.6–95.7) and NPV was 84.1% (95% CI 81.3–86.6). At median follow-up of 18.5 (IQR 13–40) months, there was no significant difference in Nurick grade between patients who had intraoperative deterioration of mMEPs and those who did not.

Conclusions

Intraoperative mMEP reduction had high specificity and low sensitivity for predicting immediate postoperative neurological deficits following IMSCT resection. However, the majority of patients who had worsening of mMEPs, recovered to their preoperative functional status or a better status at follow-up and there was no significant difference in long-term functional outcome between patients with and without intraoperative mMEP changes.