Unusual Cauda Equina and Intramedullary Disease Spread as the Only Site of Disease Recurrence in a Case of Diffuse Large B-cell Lymphoma

Secondary central nervous system (CNS) involvement in diffuse large B-cell lymphoma (DLBCL) is a rare but severe complication, typically presenting with leptomeningeal or brain parenchymal disease. We report a case of a 58-year-old immunocompetent female with high-risk DLBCL who developed neurological symptoms aft er achieving complete metabolic remission following standard chemoimmunotherapy. F-18 fluorodeoxyglucose positron emission tomography-computed tomography (F-18 FDG PET-CT) revealed multifocal FDG uptake in the cauda equina and spinal cord without systemic recurrence, confirming isolated secondary CNS lymphoma. This case highlights an uncommon pattern of CNS relapse and emphasizes the role of PET/CT in early diagnosis and guiding management.