[Splenic diffuse red pulp small B-cell lymphoma diagnosed by splenectomy initially mimicking hairy cell leukemia-Japanese variant].

A 62-year-old man presented to the hospital with thrombocytopenia, and splenomegaly was detected. His blood films prepared by natural air drying revealed medium-sized lymphocytes with unevenly distributed large and small villous projections. The cytoplasm was basophilic, nuclei were oval with clumped chromatin, and nucleoli were absent in most cells. Immune phenotypes CD19+, CD20+, CD11c+, FMC7+, IgM+, and Igκ+ were detected. TRAP stain appeared negative, IgH JH chain genes were monoclonally rearranged, and BRAF V600E mutation was not detected. On the basis of these findings, hairy cell leukemia-Japanese variant (HCL-JV) was strongly suspected. The patient was followed up for >4 years without treatment. However, because thrombocytopenia and splenomegaly gradually progressed, splenectomy was performed. Microscopic examination confirmed that the splenic white pulp was atrophic. Moreover, infiltrates comprising small-to-medium-sized atypical lymphocytes with inconspicuous nucleoli were predominantly detected in the congested red pulp. On the basis of these results and immune histochemical findings, the patient was diagnosed with splenic diffuse red pulp small B-cell lymphoma (SDRPL). Here we discussed whether the aforementioned diseases (HCL-JV and SDRPL) are the same; however, further accumulation of cases is essential to draw a definite conclusion.