The Neuronal Reserve Capacity Defines the Neurological Outcome in Motor-Eloquent Glioma Patients

Glioma patients risk incurring motor deficits, which are detrimental to quality of life and survival. The brain's varying ability to tolerate neurological stress and preserve function-conceptualized as the neuronal reserve capacity-can be profiled using navigated transcranial magnetic stimulation (nTMS). We seek to characterize this capacity by distinguishing features associated with motor stability from those that signal impending impairment. Identifying determinants of motor status can guide patient counselling, refine surgical planning, and optimize neurological outcomes.

We analyzed data of 194 patients suspected of glioma who underwent preoperative nTMS motor mapping between 2015 and 2022. Logistic regression analyses were performed to evaluate associations between perioperative motor status and patient, tumor, and neurophysiological variables.

Multivariable regression showed reduced resting motor threshold ratios (odds ratio [OR] = 0.066; 95% CI, 0.005-0.950; P = .046) and elevated recruitment curve slope ratios (OR = 1.311; 95% CI, 1.029-1.670; P = .028) to be associated with baseline-adjusted motor deficit, alongside shorter tumor-to-tract distance (OR = 0.888; 95% CI, 0.824-0.958, P = .002) and recurrent tumor status (OR = 2.724; 95% CI, 1.192-6.211; P = .017). Female sex was protective (OR = 0.265; 95% CI, 0.089-0.785; P = .017). In univariable analyses, elevated cortical silent period ratios correlated with poorer baseline status (OR = 3.895; 95% CI, 1.306-11.081, P = .014), while motor-impaired patients had a smaller motor volume in the lesioned hemisphere (r = 0.391; P = .022).

Hyperexcitability and inadequate neuronal recruitment in tumor-affected hemispheres indicate an unstable compensatory capacity and warn of impending motor impairment, with shorter tumor-to-tract distance also increasing risk. Excessive GABAergic inhibition reflects neuronal reserve exhaustion, whereas shrunken motor volume may indicate failure to initiate compensatory remodeling. More robust reserve is seen in primary tumor presentations and female sex. Integrating nTMS findings with tumor characteristics and patient history ensures a tailored approach aimed at optimizing neurological outcomes.