P11.18.A Localizing value of EEG recordings in patients with glioblastoma

Abstract

Abstract Background Glioblastoma is associated with a high risk of epileptic seizures ranging from 40% to 60%. Before the advent of modern imaging techniques, electroencephalography (EEG) was a critical component in evaluating patients with space-occupying lesions. In this retrospective single-center study, we aimed (1) to characterize a cohort of patients with glioblastoma with regards to EEG monitoring, seizure frequency and the frequency of prescribed anti-seizure medications (ASM) and (2) to assess the value of EEG as a localizing technique in patients with glioblastoma. Material and Methods We reviewed the charts of 179 patients with glioblastomas between January 1st, 2020 and January 1st, 2022, treated at the Medical University of Vienna. The diagnosis was based on MRI and/or confirmed by biopsy according to the 2016 World Health Organization Classification of Tumors of the Central Nervous System. Patients who received an in-house EEG as part of their diagnostic work-up were included if an MRI/CT scan was available (within an average time of +/-60 days). For localization, focal slowing (theta/delta activity) and/or epileptiform discharges were considered. EEG rating was performed by a board-certified electrophysiologist blinded for the diagnosis and MRI/biopsy findings. Results We included 52 patients (29.05% of screened cohort) with at least one EEG and MRI or CT scan performed before or after EEG, following inclusion criteria (median: 2 days; mean: 6 days; range: -29 to 52), in the final analysis. Clinical seizure activity and/or epileptiform discharges on EEG were detected in 46 patients (88.46%), and 48 patients (92.31%) were on ASM. An IDH-wildtype glioblastoma was diagnosed in 45 patients (86.54%), 4 had an IDH-mutant glioblastoma (7.69%), and in 3 patients, IDH-status was unknown (5.77%). In 22 patients (42.31%), biopsy revealed a positive MGMT promoter methylation status, while 28 were unmethylated (53.84%), and two patients had an unknown MGMT promoter methylation status (3.85%). Intermittent and/or continuous focal slow-wave activity was registered in 45 patients (86.54%). In comparison, epileptiform discharges could only be found in 13 patients (25%). When compared to MRI/CT scans, the hemispheric tumor localization could be determined in 42 cases (80.77%). Moreover, the affected brain lobe was accurately predicted in 35 patients (67.31%). Three patients had diffuse EEG changes (5.77%), and EEG was unremarkable in 7 patients (13.46%). Conclusion Overall, our presented data indicate that the hemispheric localization of glioblastoma can be reliably predicted by EEG recordings, while a precise (brain lobe-specific) localization was only possible in around two-thirds of cases.