Intravascular Large B–cell Lymphoma Diagnosed Incidentally after a Renal Biopsy: A Case Report of a Rare and Elusive Malignancy

Intravascular large B-cell lymphoma (IVLBCL) is a form of diffuse large B-cell lymphoma (DLBCL) characterized by the proliferation of malignant B-cells within the lumen of small blood vessels. With an incidence rate of one in a million, it is one of the rarest forms of DLBCL. This rarity, combined with the absence of extravascular tumor masses or circulating malignant cells in the peripheral blood and potential involvement of multiple organs, makes the diagnosis of IVLBCL exceptionally difficult. We discuss that case of a 64-year-old female who presented with symptoms of altered mental status, expressive aphasia, and fatigue. She was also found to have normocytic anemia with elevated hemolysis markers. Over a period of months, her neurological symptoms and anemia with elevated hemolysis markers persisted despite repeated hematological, infectious, and neurological workup. Overall, we hope to highlight the unusual clinical manifestations of IVLBCL, as early diagnosis and treatment can be lifesaving.