Correlation of Intraoperative Neuromonitoring (IONM) Signal Changes with Clinical Outcomes in Patients with Compressive Cervical Myelopathy: A Prospective Study
Authors: Basu Saumyajit , Guduru Aditya Vardhan , Hanasoge Vikas , Joshi Piyush , Sarangi Trinanjan , Chakroborthy Suraj 
Published: January 2025

Abstract

Background:
Compressive myelopathy results from chronic segmental compression of the spinal cord due to various factors like disk herniation, spondylosis, degenerative changes, ossification of the ligamentum flavum, and ossification of the posterior longitudinal ligament. Surgery, in the form of decompression with or without fusion, is recommended for these patients. Intraoperative neuromonitoring (IONM) is an important tool to evaluate spinal cord integrity during surgery. Few studies have shown the correlation between neurophysiological signal changes during cervical spinal cord decompression for cervical compressive myelopathy and postoperative functional outcomes. Therefore, the purpose of this study purpose was to prospectively evaluate the correlation between the variations in the IONM signals and postoperative neurological recovery in patients with cervical compressive myelopathy undergoing surgery.

Materials and Methods:
The study included 58 patients with cervical compressive myelopathy who underwent decompression and fusion surgery under IONM guidance. The baseline IONM data were compared to the final data after wound closure, with additional intraoperative changes noted. Patients were divided into three groups: Group 1—no change in the amplitude of motor-evoked potential (MEP) at the end of surgery compared to baseline MEP (n = 45), group 2—improvement in the amplitude of MEP at the end of surgery compared to baseline MEP (n = 5), and group 3—reduction in the amplitude of MEP at the end of surgery compared to baseline MEP (n = 8). The study was conducted over a 12-month period, from January 2022 to December 2022, with a minimum follow-up of 6 months. Clinical evaluation of these patients preoperatively and postoperatively at 1 month and 6 months were done using modified Japanese Orthopedic Association (mJOA) and Nurick grading. Statistical analysis of quantitative data was presented as mean, and standard deviation, and qualitative data was presented as frequency (percentage). Paired t-tests were used for the comparison of preoperative and postoperative functional scores. One-way Analysis of variance (ANOVA) tests with Bonferroni post hoc analyses were performed for comparison between the three groups.

Results:
Preoperatively, there was no statistically significant difference between the three groups in mJOA score and Nurick grade. The mJOA score recovery rate (RR) at 6 months was 30.74% in group 1 and 37.34% in group 2 (P < 0.001). In group 3, the improvement was 11.71% and was not statistically significant. Nurick grading showed significant improvement at 6 months compared to preoperative in group 1 (2.5 at 6 months vs. 3.4 preoperatively, P < 0.001) and group 2 (2.6 at 6 months vs. 3.4 preoperatively, P = 0.01). However, no significant improvement was found in group 3 (2.8 at 6 months vs. 3.4 preoperatively, P = 0.14). Complications occurred in 11 patients (24.44%).

Conclusion:
Patients who had diminished IONM signals at the end of surgery for cervical myelopathy, as compared to the baseline, did not have a significant improvement in their mJOA score and Nurick grading by 6 months postoperatively. In contrast, patients with no variation or improvement in IONM signals showed significant neurological recovery.