Prevalence of intravascular large B-cell lymphoma with bone marrow involvement at initial presentation.

We used immunohistochemical analysis to investigate 146 bone marrow (BM) clot specimens from patients with fever of unknown origin (FUO) (n = 124) or hemophagocytic syndrome (HPS) (n = 22). Intravascular lymphoma (IVL) primarily involving BM was detected in 12 (8.2%) of the 146 patients. Diagnosis was based on the presence of CD20+ and CD79a+ tumor cells confined within the lumina of sinuses and surrounded by CD34+ endothelial cells. Of the 12 IVL cases, 6 were CD5+; of these 6 CD5+ cases, 5 were positive for vimentin. The finding of a considerably high prevalence of IVL tumor cells in BM from patients with FUO or HPS suggests that immunohistochemical examination of BM may be helpful in the diagnosis of IVL in these patients. Vimentin coexpression in CD5+ IVL might be evidence of origin from a subset of prefollicular B-cells.