Objectives: Chimeric Antigen Receptor (CAR)-T cell therapy is used to treat refractory haematological malignancy (Feins et al., 2019). Neurotoxicity, encephalopathy, and seizures often follow CAR-T treatment (Grant et al., 2022; Tallantyre et al., 2021). Electroencephalography (EEG) is commonly used to assess patients developing these neurological complications. Our aim was to assess what value, if any, EEG offers for people undergoing CAR-T treatment in clinical practice, including possible diagnostic, management, and prognostic roles.
Methods: All patients who developed CAR-T neurotoxicity referred for EEG were eligible for inclusion. Reasons for EEG referral and qualitative EEG findings were analysed and reported. A validated quantitative approach was used to grade EEG severity of encephalopathy (Van der Rijt et al., 1984). The relationship between objective quantitative EEG (qEEG) encephalopathy grade and clinical neurotoxicity (Immune effector Cell-Associated Neurotoxicity Syndrome; ICANS) scale was determined retrospectively. The prognostic ability of qEEG grade was assessed for survival and functional performance (Eastern Cooperative Oncology Group; ECOG) scores (Oken et al., 1982), using Pearson correlation and Area Under Receiver Operating Characteristic (AUROC) curve statistical analyses. 
Results: Twenty-eight patients with 53 EEG recordings were included. Common reasons given on EEG referrals were possible seizure diagnosis (n=38), low GCS (n=8), and superimposed cerebral infection (n=4). Four focal seizures were detected on three (3/53; 5.7%) EEGs. There was a moderately positive correlation between qEEG grade and ICANS grade (r = +0.41, p = .030). qEEG grade could not predict survival at 3 months (Area Under Curve; AUC = 0.673) or 6 months (AUC = 0.578), nor could it predict functional status at 1 month (r = +0.40; p = .080), at 3 months (r = +0.19; p = .439), or time to return to baseline (r = +0.32; p = .156).
Conclusions: EEG was useful in seizure diagnosis. Objective qEEG grading has a moderate correlation with clinical ICANS grade, suggesting a possible role as a specific biomarker of encephalopathy/neurotoxicity. qEEG was unable to prognosticate on survival or functional status in our small series of patients with CAR-T related neurotoxicity.