RESUMO
Intravascular large B-cell lymphoma (IVLBCL) is a rare hematological malignancy where its development in the intravascular environment is the main characteristic. Despite its ability to affect multiple organic systems, there is a tropism for the central nervous system, which may be related to several clinical syndromes, making this condition a great mimic and consequently a diagnostic challenge. Rapidly progressive dementia may be one of the presenting phenotypes of IVLBCL. This case report aims to highlight the main red flags, such as sustained elevation of lactate dehydrogenase, organomegaly and specific lesions with vasculitis-like bleeding, all that can be used as clinical clues to direct the differential diagnosis. In addition, it reinforces the role of early brain biopsy in this context, since IVLBCL is a treatable disease.