1. Objective
Intraoperative neurophysiological monitoring (IONM) is commonly used technique for assessing nervous system during spinal or brain surgery. The consensus about the alarm criteria of motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) have been evolving continuously to predict the poor functional prognosis after surgery. With no previous study, this study aims to find out whether the increase of the amplitude of MEPs can imply favorable prognosis in spinal cord tumor surgery
2. Methods
1) Patients
This is a retrospective cohort study between March 2016 and February 2018 in one institute. The IONM was performed in 115 patients with spinal cord tumor. With excluding 43 patients who were lost to follow up, medical data of 72 patients were analyzed. The strengths of bilateral 10 key muscles by manual muscle test documented a day before (Motorpre), 48 hours (Motor48hrs) and 4 weeks (Motor4wks) after the surgery were reviewed
2) IONM data
The final peak-to-peak amplitudes changes of the N20 (deltoid or abductor polices brevis) or P37 (tibialis anterior or abductor halluces) of MEPs were reviewed. The amplitude changes at the end of monitoring compared to the baselines in each muscle were analyzed. Among the changes of MEPs in several muscles, the minimum and maximum changes were set to MEPmin (%) and MEPmax (%).
3) Statistical Analysis
Pearson’s correlation analysis was used to find the correlation between Motorpre, Motor48hrs, Motor4wks, MEPmin, MEPmax, and bleeding amount
3. Results
The difference of Motor48hrs from Motorpre (Motor48hrs-pre) positively correlated with MEPmin (Pearson correlation coefficient 0.32 and P=0.01) (Fig. 1 & Table 1), suggesting that the smaller the difference of MEPs amplitude, the less recovery of muscle strength. Additionally, there was a negative correlation between the amount of bleeding and MEPmin (Pearson correlation coefficient -0.28 and P=0.02) (Fig 2 & Table 1), 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. Also, it showed no significant correlation between amount of bleeding and Motor48hrs-pre (P=0.19). There was no significant correlation between the difference of Motor4wks and Motorpre (Motor4wks –pre) and MEPmin (P=0.06) or MEPmax (P=0.40), respectively (Table 1)
Conclusion
This is the first study to investigate the correlation between amplitude increase in MEPs and the amount of motor recovery. This study showed that the recovery of muscle strength was less when the increase of MEPs amplitude was small, and that the improvement of MEPs amplitude was less when the amount of bleeding was large. However, there was no direct correlation between the amount of bleeding and improvement in muscle strength maybe due to small sample size and small correlation coefficients. For delicate analysis, further studies including various parameters of IONM would be needed |
