Altered Motor Excitability in Patients With Diffuse Gliomas Involving Motor Eloquent Areas: The Impact of Tumor Grading

Neurosurgery 88( 1) 2021: 183–192

Diffuse gliomas have an increased biological aggressiveness across the World Health Organization (WHO) grading system. The implications of glioma grading on the primary motor cortex (M1)-corticospinal tract (CST) excitability is unknown.

OBJECTIVE: To assess the excitability of the motor pathway with navigated transcranial magnetic stimulation (nTMS).

METHODS: Retrospective cohort study of patients admitted for surgery with diffuse gliomas within motor eloquent areas. Demographic, clinical, and nTMS-related variables were collected. The Cortical Excitability Score (CES 0 to 2 according to the number of abnormal interhemispheric resting motor threshold (RMT) ratios) was calculated for patients where bilateral upper and lower limb mapping was performed.

RESULTS: A total of 45 patients were included: 9 patients had a low-grade glioma and 36 patients had a high-grade glioma. The unadjusted analysis revealed an increase in the latency of the motor evoked potential of the lower limb with an increase of theWHOgrade (P = .038). The adjusted analysis confirmed this finding (P = .013) and showed a relation between the increase in the WHO and a decreased RMT (P = .037) of the motor evoked responses in the lower limb.When CES was calculated, an increase in the score was related with an increase in the WHO grade (unadjusted analysis—P = .0001; adjusted analysis— P = .001) and in isocitrate dehydrogenase (IDH) wild-type tumors (unadjusted analysis— P = .020).

CONCLUSION: An increase in the WHO grading system and IDH wild-type tumors are associated with an abnormal excitability of the motor eloquent areas in patients with diffuse gliomas.