Evaluation of cortical excitability patterns in patients undergoing glioblastoma resection in the motor area

Background: Brain tumors adjacent to the primary motor cortex may alter corticospinal physiology through mass effects, pathway disruption and maladaptive plasticity. Preoperative transcranial magnetic stimulation (TMS) maps cortical excitability more accurately than fMRI does and correlates with intraoperative stimulation, but it is unclear which TMS parameters predict postoperative motor outcomes. We investigated whether preoperative TMS cortical excitability measures differ from healthy norms and whether they identify signals potentially useful for predicting postoperative motor deficits. Methods: This was a retrospective, single-center observational study of consecutive adult patients (18–70 years) with glioblastoma adjacent to the precentral gyrus who underwent standardized preoperative TMS mapping (N = 60). The measured parameters included the resting motor threshold (RMT), MEP amplitudes at 120% and 140% RMT, the MEP140/120 ratio, paired-pulse relative MEPs at interstimulus intervals of 2, 4, 10 and 15 ms (Rel-02, Rel-04, Rel-10, Rel-15), short-interval intracortical inhibition (IICI) and intracortical facilitation (ICF). Patient values were compared to those of a healthy Brazilian reference cohort via robust one-sample median tests and age-stratified analyses; categorical comparisons were performed with normal ranges in the literature (Cueva et al.). Variables with correlation coefficients |r|>0.2 were considered for multivariable logistic modeling to explore associations with postoperative motor deficits. Results: Sixty patients were analyzed. Compared with the healthy cohort, the ill hemisphere showed significant alterations in paired-pulse and intracortical measures. In categorical analyses using established normal ranges, the ill hemisphere had significantly lower odds of being classified as “Low” (vs “High”) for Rel-04 (OR 0.21; 95% CI 0.07–0.57; p = 0.0067), Rel-15 (OR 0.25; 95% CI 0.10–0.63; p = 0.0117), IICI (OR 0.27; 95% CI 0.10–0.68; p = 0.0216) and ICF (OR 0.30; 95% CI 0.12–0.72; p = 0.0238). Age-stratified robust median tests versus healthy medians demonstrated multiple significant deviations—most prominently for MEP amplitudes and relative paired-pulse indices in patients <50 years. Several excitability measures met prespecified correlation thresholds and were entered into multivariable modeling (the results are reported in the main text). Conclusions: Preoperative TMS reveals consistent alterations in paired-pulse measures and intracortical inhibition/facilitation in glioblastomas adjacent to the motor cortex. Rel-04, Rel-15, IICI and ICF differ from healthy norms and merit prospective evaluation as predictors of postoperative motor outcomes. Future prospective studies should validate these parameters and determine their incremental predictive value for surgical planning and rehabilitation stratification.