Extensive myelitis with eosinophilic meningitis after Chimeric antigen receptor T cells therapy

Immune effector cell‐associated neurotoxicity syndrome (ICANS) is a frequent adverse event after Chimeric antigen receptor T cells (CAR‐T cells). A patient treated with anti‐CD19 CAR‐T cells for a refractory mantle cell lymphoma presented at Day 8 post‐infusion with extensive myelitis. Unusual eosinophilia was disclosed in the patient's cerebrospinal fluid. After treatment with methylprednisolone and siltuximab, a decrease in clinical symptoms and magnetic resonance imaging lesions were obtained. This unprecedented presentation of eosinophilic meningitis after CAR‐T cells therapy highlights the need for a better understanding of the physiopathology of ICANS, especially to identify potentially targetable pathways.