ABNORMAL CORTICAL EXCITABILITY IS ASSOCIATED WITH DECREASED OVERALL SURVIVAL IN PATIENTS WITH GLIOBLASTOMA

Abstract AIMS Navigated transcranial magnetic stimulation (nTMS) is a well-established technique for motor cortex mapping and assessing motor tract integrity in patients with brain tumours. Pre-surgical nTMS mapping in patients with glioma has shown an altered interhemispheric excitability that correlates well with WHO grade. The aim of this study is to correlate the preoperative nTMS findings with overall survival (OS) in patients with motor-eloquent brain tumours operated at our institution. METHOD We conducted a retrospective cohort study using electronic patient records to search for all patients with a motor-eloquent brain tumour resected between 2017 and 2023. We included all adult patients (>18 years) with pre-operative nTMS mapping and a tissue diagnosis. Two nTMS measures of cortical excitability were assessed; cortical excitability score (CES) and the intraM1 excitability score (IMES). Our outcome measure was OS. RESULTS 160 patients fulfilled the inclusion criteria (mean age 48.34 years). The commonest tumour histology was glioblastoma (n=51; 32%). Among patients with diffuse gliomas, IDH was mutated in 59% patients and MGMT was methylated in 61%. Majority of patients (62.5%) underwent gross total resection. Resting motor thresholds (RMTs) for both upper and lower limbs between the tumour and healthy side were not significantly different. Interhemispheric RMT ratio in the upper limbs was abnormal in 60.93% patients and in the LLs was abnormal in 57.14%. A higher CES was related to lower overall survival (p=0.04). A subgroup analysis showed this was particularly the case among patients with a diagnosis of Glioblastoma (p=0.015). When adjusted for cofounding factors EOR, MGMT methylation and age, both CES and IMES were inversely related to OS (p=0.002). CONCLUSION A higher CES and IMES is related with poor overall survival in patients with Glioblastoma even when other cofounding factors affecting OS are considered. This information can be used when counselling patients and planning surgical approach to motor-eloquent tumours.