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 MEPmin (%) and MEPmax (%). Strengths of bilateral 10 key muscles which were documented
a day before (Motorpre), 48 h (Motor48h) and 4 weeks (Motor4wk) after the surgery were reviewed.
Results: Difference of Motor48h from Motorpre (Motor48h-pre) and Motor4wk from Motorpre (Motor4wk-pre) positively correlated
with MEPmin, suggesting that smaller the difference of MEPs amplitude, less recovery of muscle strength. There was a
negative correlation between the amount of bleeding and MEPmin, indicating that the greater the amount of bleeding, the
smaller the MEPmin, 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.