Neuro-oncologists face substantial challenges when predicting clinical trajectories for patients presenting with aggressive high-grade cerebral neoplasms. Although molecular profiling offers indispensable insights, evaluating functional electrophysiological markers like cortical excitability glioblastoma parameters provides an innovative dimension for neurosurgical decision-making. Preoperative navigated transcranial magnetic stimulation (nTMS) has long supported safe resections adjacent to eloquent motor pathways. However, emerging clinical evidence indicates that physiological disruptions captured during non-invasive stimulation can independently forecast survival outcomes before resection occurs.

Prognostic Significance of Cortical Excitability Glioblastoma Metrics

Traditionally, clinicians rely on histomolecular criteria, patient age, and performance status to formulate neuro-oncological prognoses. However, tumors situated within motor-eloquent cortex trigger complex physiological shifts in local and distant neural circuitry. Researchers evaluated whether non-invasive functional mapping could offer predictive value beyond standard clinicopathological variables. Specifically, investigators evaluated two specialized metrics: the IntraM1 Excitability Score (IMES) and the Cortical Excitability Score (CES).

Consequently, these quantitative indices reflect distinct aspects of corticospinal tract integrity and interhemispheric physiological balance. The primary motor cortex exhibits delicate functional connections that invasive glioma cells easily disrupt. When glioblastomas infiltrate motor regions, they alter resting motor thresholds and create severe excitability imbalances between cerebral hemispheres. Therefore, assessing baseline electrical reactivity before surgical incision provides critical insight into tumor aggressiveness. Furthermore, this physiological approach expands the clinical utility of nTMS far beyond conventional anatomical localization. In addition, neurosurgeons can now evaluate both functional operability and underlying patient prognosis during a single preoperative mapping appointment. Ultimately, these functional measurements bridge the gap between electrophysiology and clinical oncology. Moreover, understanding these neurophysiological alterations allows surgical teams to anticipate postoperative neurological deficits and optimize individualized counseling.

Methodological Framework and Patient Stratification

The clinical investigation examined seventy-seven consecutive adult patients diagnosed with motor-eloquent WHO grade 4 IDH-wildtype glioblastoma between 2018 and 2024. The cohort featured a mean age of 55.4 years and included forty-one male patients. Each patient underwent comprehensive preoperative nTMS testing before surgical resection to evaluate cortical motor maps. During these evaluations, neurophysiologists systematically determined resting motor thresholds across both cerebral hemispheres.

In addition, examiners derived the IMES to capture local excitability variations within the primary motor strip adjacent to the neoplasm. Meanwhile, the CES quantified broader interhemispheric excitability discrepancies between the affected and healthy hemispheres. Importantly, surgeons performed maximally safe tumor resections guided by advanced intraoperative neuro-navigation. The investigators followed the cohort over extended surveillance, recording a mean overall survival of 20.5 months. Furthermore, the researchers meticulously documented key clinical variables, including baseline neurological deficits, patient age, and sex. They also confirmed molecular profiles, specifically verifying IDH mutation absence and MGMT promoter methylation status. Consequently, this rigorous methodological structure allowed precise statistical adjustments and minimized potential confounding elements during subsequent survival analyses.

Survival Correlations and Multivariate Statistical Findings

Univariate survival analysis demonstrated significant associations between baseline electrophysiological parameters and patient outcomes. Specifically, patients with lower IMES values experienced significantly poorer overall survival following surgical resection. In contrast, higher CES values correlated with accelerated disease progression and reduced survival times. Therefore, both markers demonstrated clear prognostic utility during initial statistical assessments.

To validate these observations, the researchers executed comprehensive multivariable Cox proportional hazards regression models. Importantly, the analysis controlled for established clinical covariates, including patient age, sex, preoperative neurological deficits, MGMT methylation, and resection extent. Even after rigorous statistical adjustment, both neurophysiological metrics remained robust independent prognostic indicators. Specifically, lower IMES preserved an independent hazard ratio of 0.16 (p = 0.003). Meanwhile, higher CES demonstrated an independent hazard ratio of 2.63 (p = 0.034). Furthermore, bilateral nTMS mapping markedly improved twelve-month survival prediction compared to unilateral testing alone. Thus, comprehensive bilateral stimulation protocols capture critical interhemispheric interactions that unilateral assessments inevitably overlook. These compelling findings highlight the strong predictive capacity of non-invasive cortical mapping in routine neuro-oncological evaluation. Accordingly, clinicians gain valuable prognostic clarity that surpasses standard radiological imaging alone.

Biological Mechanisms Linking Excitability and Aggressive Biology

The physiological connection between cortical excitability and glioblastoma progression involves complex neuro-glioma interactions within the tumor microenvironment. Recent basic neuroscience demonstrates that malignant glioma cells form functional synaptic connections with surrounding healthy neurons. Consequently, active glutamatergic signaling promotes glioma proliferation, migration, and invasive growth into adjacent parenchyma. Simultaneously, invasive tumor cells secrete neurotoxic glutamate, which impairs surrounding inhibitory interneurons and generates focal hyperexcitability.

In addition, this localized neurochemical disinhibition destabilizes normal network architecture throughout the motor cortex. Thus, a high CES reflects marked interhemispheric functional asymmetry caused by aggressive tumor infiltration and synaptic restructuring. Conversely, a decreased IMES indicates extensive corticospinal tract disruption and severe peritumoral axonal degradation. When glioblastomas display higher invasive velocity, they disrupt local motor networks more profoundly before clinical symptoms manifest. Therefore, nTMS metrics serve as an electrophysiological mirror of underlying biological aggressiveness and cellular infiltration. Furthermore, these non-invasive electrical measurements uncover profound synaptic derangements that conventional structural magnetic resonance imaging cannot visualize. Ultimately, electrical excitability reveals the true functional impact of the tumor on host cerebral networks.

Translational Implications for Neurosurgical Care

These compelling findings introduce transformative opportunities for multidisciplinary neuro-oncology teams in tertiary medical centers. Currently, neurosurgeons utilize nTMS predominantly for functional mapping and trajectory planning. However, incorporating cortical excitability scores into initial patient workups provides an immediate functional prognostic stratification. Because nTMS is non-invasive and well-tolerated, clinical teams can readily implement excitability profiling into established outpatient pathways.

Moreover, identifying high-risk physiological profiles before surgery helps clinicians personalize aggressive management strategies. For instance, patients demonstrating adverse excitability metrics may benefit from tailored surgical margins, intensified adjuvant radiation, or early enrolment into innovative clinical trials. In addition, neurosurgeons can utilize these electrophysiological indices to refine preoperative risk counseling for patients and their families. Transparent discussions regarding functional prognosis foster realistic expectations and support shared decision-making. Furthermore, longitudinal nTMS tracking during post-surgical follow-up could potentially detect early tumor recurrence before radiological changes appear on surveillance imaging. As Indian neurosurgical centers increasingly adopt navigation technologies, integrating excitability analysis represents a cost-effective, high-impact clinical advancement. Consequently, neuro-oncologists can establish comprehensive management plans that effectively harmonize maximal safe surgical resection with realistic survival expectations.

Future Directions and Integration with Surgical Planning

Although these retrospective findings offer compelling evidence, future research must address several methodological questions before universal implementation. First, prospective multicenter trials must validate the predictive accuracy of IMES and CES across diverse demographic populations. Standardizing stimulation protocols, coil orientations, and resting motor threshold definitions remains essential to ensure reproducible results across centers.

In addition, researchers should investigate how antiepileptic medications and tumor-associated edema influence cortical excitability measurements. Because many glioblastoma patients receive membrane-stabilizing anticonvulsants, establishing standardized correction factors will enhance diagnostic consistency. Furthermore, combining nTMS excitability profiling with advanced diffusion tensor imaging and resting-state functional MRI could create multidimensional predictive models. Such multimodal frameworks would capture structural connectivity, functional coherence, and electrophysiological reactivity simultaneously. Notably, future interventional trials could explore whether neuromodulation therapies, such as repetitive transcranial magnetic stimulation, can alter perioperative cortical excitability and improve clinical trajectories. Ultimately, decoding the electrophysiology of glioblastoma will redefine our prognostic paradigms and guide innovative therapeutic strategies. Therefore, ongoing neurophysiological investigation promises to transform static anatomical evaluations into dynamic, functional assessments that directly improve patient outcomes.

Frequently Asked Questions

How does nTMS measure cortical excitability before surgery?

Clinicians position a stereotactic magnetic coil over the patient scalp to stimulate the primary motor cortex while recording electromyographic responses from peripheral muscles. By systematically adjusting magnetic intensity, investigators measure resting motor thresholds. This physiological assessment quantifies both interhemispheric balance and regional corticospinal tract excitability without requiring invasive operative exposure.

Why does altered cortical excitability influence overall survival?

Pathological glioma growth disrupts local synaptic networks and impairs peritumoral gamma-aminobutyric acid inhibitory neurotransmission. Consequently, aggressive tumors induce pronounced regional hyperexcitability and severe functional network fragmentation. These neurophysiological alterations reflect rapid invasive cellular proliferation, extensive microenvironmental stress, and resistance to standard oncological therapies, which directly shortens overall survival.

Can nTMS excitability scores replace established molecular glioblastoma markers?

No, functional excitability metrics do not replace histomolecular analysis. Instead, parameters like IMES and CES complement established survival determinants such as MGMT promoter methylation and resection extent. By integrating functional neurophysiology with traditional molecular oncology, multidisciplinary neuro-oncology teams achieve more precise risk stratification and personalize individualized therapeutic regimens.

Disclaimer: This content is for informational and educational purposes only and should not be considered medical advice. Always consult a qualified healthcare provider for diagnosis and treatment decisions. Refer to the latest local and national guidelines for clinical practice.

References

Lavrador JP et al. nTMS-determined cortical excitability is associated with overall survival in patients with motor-eloquent glioblastoma. J Neurooncol. 2026 Sep 23. doi: 10.1007/s11060-026-05806-x. PMID: 42776377.

Krieg SM et al. Cortical Excitability by Navigated Transcranial Magnetic Stimulation in Patients With Brain Tumor. Front Neurol. 2020;11:582262.

Rosenstock T et al. Comparison of anatomical-based vs. nTMS-based risk stratification model for predicting postoperative motor outcome and extent of resection in brain tumor surgery. Front Oncol. 2022;12:875161.