Increased Intraoperative Motor Evoked Potentials and Motor Recovery after Spinal Cord Tumor Removal

Objective: To evaluate whether the increase of the amplitude of motor evoked potentials (MEPs) during surgery can imply favorable prognosis postoperatively in spinal cord tumor surgery. Method: MEPs were monitored in patients who underwent spinal cord tumor surgery between March 2016 and March 2018. Amplitude changes at the end of monitoring compared to the baselines in limb muscle were analyzed. Minimum and maximum changes were set to MEP min (%) and MEP max (%). Strengths of bilateral 10 key muscles which were documented a day before (Motor pre ), 48 h (Motor 48h ) and 4 weeks (Motor 4wk ) after the surgery were reviewed. Results: Difference of Motor 48h from Motor pre (Motor 48h-pre ) and Motor 4wk from Motor pre (Motor 4wk-pre ) positively correlated with MEP min , suggesting that smaller the difference of MEPs amplitude, less recovery of muscle strength. There was a negative correlation between the amount of bleeding and MEP min , indicating that the greater the amount of bleeding, the smaller the MEP min , implying that MEPs amplitude is less likely to improve when the amount of bleeding is large. It also showed significant difference between patients with improved or no change of motor status and patients with motor deterioration after surgery according to anatomical tumor types. Conclusion: Improve of muscle strength was less when the increase of MEPs amplitude was small, and improvement of MEPs amplitude was less when the amount of bleeding was large. Correlation between changes of status of muscle strength after surgery and tumor types was observed. With amplitude increase in MEPs monitoring, restoration of muscle strength can be expected.