The Improvement of Intraoperative Motor Evoked Potential after Decompression in Cervical Compressive Myelopathy: Its Significance and Related Factors

Objective: This study investigated the relationship between intraoperative motor evoked potential (MEP) improvement after decompression surgery for cervical compressive myelopathy (CCM) and postoperative neurological outcomes, and preoperative factors influencing MEP improvement.Methods: MEP amplitudes were measured prospectively before and after decompression in 38 patients with CCM. The patients were categorized into three groups according to whether the intraoperative MEP slightly decreased, slightly increased, or significantly increased. Functional outcomes were assessed using the recovery rate (RR) and absolute improvement (AI) of the modified Japanese Orthopaedic Association score on postoperative days (PODs) 7 and 28. The preoperative characteristics and intraoperative MEP changes among the three groups were compared. Additionally, the correlation between the increase in MEP amplitude during surgery and the extent of improvement in functional outcomes was investigated.Results: The significantly increased MEP group had a lower baseline MEP amplitude (152.46 µV; p=0.009). In the slightly decreased MEP group, the RR was 27.98 ± 32.29% at POD 7 (p=0.010) and 11.61 ± 69.84% at POD 28 (p=0.200); the AI was 0.79 ± 0.80 at POD 7 (p=0.010) and 0.79 ± 1.42 at POD 28 (p=0.100). In the slightly increased MEP group, the RR was 23.75 ± 28.36% at POD 7 (p=0.040) and 28.47 ± 43.38% at POD 28 (p=0.070); the AI was 1.00 ± 1.21 at POD 7 (p=0.030) and 1.08±1.88 at POD 28 (p=0.100). In the significantly increased MEP group, the RR was 41.06 ± 32.01% at POD 7 (p=0.009) and 59.78 ± 34.52% at POD 28 (p=0.006); the AI was 3.08 ± 2.07 at POD 7 (p=0.009) and 4.33 ± 2.54 at POD 28 (p=0.006). Greater intraoperative MEP improvement correlated with better postoperative recovery at 1 month (RR, p=0.010; AI, p<0.001).Conclusion: Intraoperative MEP monitoring is valuable for predicting postoperative neurological outcomes in CCM patients, particularly those with lower baseline MEP amplitudes. Significant intraoperative MEP improvements are associated with better functional recovery. These findings underscore the importance of MEP monitoring in optimizing surgical strategies and predicting neurological recovery.