gms | German Medical Science

Objective: Glioma-induced functional reorganization (FR) is recently being discussed more frequently. However, there are only a few prospective longitudinal studies. The present study therefore investigates FR of cortical motor areas after the resection of motor-eloquent gliomas by navigated transcranial magnetic stimulation (nTMS).

Methods: We included 10 patients (mean age 49 ± 16 years) with motor-eloquent gliomas (6 low- and 4 high-grade) scheduled for microsurgical resection. nTMS motor mappings and measurements of clinical motor function were performed preoperatively as well as 3, 6, and 12 months after surgery.

Results: Functional motor areas in terms of nTMS motor mappings shifted in comparison to the preoperative situation on the antero-posterior axis within the same hemisphere (mean 8.2 ± 2.1 mm), and away from the resection cavity. The shifting was mainly observed at the 3 and 6 months follow-up but also continues 12 months after surgery. We also found a shift of the motor function to the unaffected hemisphere in one patient, resulting in a right-sided cortical area showing nTMS-induced motor evoked potentials (MEPs) of right-sided hand muscles. The excitability of the motor system, measured by the resting motor threshold (rMT), has shown to be very robust and reproducible in case of an intact motor system (mean difference 4.27 V/m). In contrast, the rMT decreased in patients with an improvement of clinically investigated motor function and increased in those, who showed a worsening motor function postoperatively (mean difference 12.82 V/m).

Conclusion: Our preliminary results show that nTMS is an appropriate technique to visualize FR in glioma patients. Further patients must be investigated to confirm these first results and to draw further conclusions on the impact of FR and plasticity.