Isolated CNS relapse of medullary aggressive high-grade B-cell lymphoma on ¹⁸F-FDG-PET/CT

This is a case of high-risk, aggressive, high-grade medullary B-cell lymphoma presenting with new onset of neurological dysfunction following initial complete response to the standard chemoimmunotherapy. A whole-body re-staging PET using fluorodeoxyglucose (¹⁸F-FDG) integrated with computed tomography (¹⁸FDG-PET/CT) performed with clinical suspicion of arachnoiditis, eloquently demonstrated unequivocal multifocal FDG uptake by the spinal cord without evidence of systemic recurrence, leading to a clinical diagnosis of secondary CNS lymphoma, which is a rare complication of DLBCL with ominous prognosis. Four cycles of Modified-MATRIX protocol resulted in a halt in fulminant course of the disease and the patient experienced slight reversal of the neurological deficits, although not deemed clinically fit for a repeat ¹⁸FDG-PET/CT due to his poor general well-being. Repeat MRI was suggestive of partial recovery, however. The clinical stability was proven short-lived, and the patient experienced progressive lower limb weakness only 3 weeks after discharge following his last cycle of treatment. Isolated CNS relapse of lymphoma is a rare occurrence in the literature. The CNS recurrence is more often leptomeningeal or confined to the brain parenchyma rather than the spinal cord. The role of ¹⁸FDG-PET/CT in the diagnostic algorithm of secondary CNS lymphoma is unclear and its significance in risk stratification and assessing the response to treatment has not been evaluated. This case report illustrates the imaging findings of a more unusual form of the disease with multifocal intramedullary involvement of the spinal cord, and highlights imaging features of this rare condition with ¹⁸FDG-PET/CT and MRI to support decision making in good clinical practice.