Diagnostic value of D-wave and motor evoked potentials in intramedullary spinal cord tumor surgery: a temporal analysis of predictive accuracy.
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OBJECTIVE: The surgical resection of intramedullary spinal cord tumors (IMSCTs) is associated with significant morbidity. Intraoperative neuromonitoring (IONM) with transcranial myogenic motor evoked potentials (m-MEP) and D-wave aims to reduce new postoperative motor deficits. Still, their comparative ability to predict short- and long-term outcomes is incompletely defined. We evaluated the diagnostic performance of m-MEP and D-wave monitoring at multiple postoperative time points and examined their influence on intraoperative decision-making. METHODS: In this single-institution observational study (2017-2024), we included 44 patients undergoing resection of IMSCTs with multimodal IONM. Neurological status was assessed using Medical Research Council (MRC) grade and Modified McCormick Scale (MMS) preoperatively, immediately (0-3 days), at discharge (7-14 days), and at ≥ 6 months follow-up. Statistical analyses were used to correlate the postoperative deficits with attenuation of m-MEP and D-wave potentials during surgery. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated and compared using McNemar's test. RESULTS: Mean age was 36.6 ± 15.1 years; mean follow-up was 14.5 ± 7.2 months. IONM attenuation occurred in 20 patients (45.5%): m-MEP drop in 20 (45.5%) and D-wave amplitude reduction in 6 (13.6%); no case had a complete loss of D-wave. Immediate postoperative motor deficits occurred in 72% (MRC) and 38.6% (MMS), declining to 15% and 9% at follow-up, respectively. D-wave attenuation correlated significantly with deficits immediately (p = 0.02) and at discharge (p = 0.027) but not at follow-up (p = 0.257). m-MEPs demonstrated higher sensitivity (51-66%) but lower specificity than D-waves across time points. D-waves showed lower sensitivity (35-75%) but consistently high specificity (95-100%). D-waves demonstrated superior diagnostic accuracy at follow-up compared with m-MEPs (84% vs. 59% on MRC; 93% vs. 64% on MMS; p < 0.001). The PPV of both modalities declined over time, while the NPV and sensitivity improved at the last follow-up. False positives were more common with m-MEPs (30-40%) than with D-waves (0-5%). CONCLUSIONS: The predictive accuracy of IONM varies with time following surgery. m-MEPs are more sensitive for detecting immediate postoperative deficits, while D-waves are more specific and have superior predictive accuracy for long-term motor outcomes. Their complementary roles highlight the importance of multimodal monitoring as a surgical guide rather than a restrictive determinant of resection. CLINICAL TRIAL NUMBER: Not applicable.