[Polyclonal B-cell lymphocytosis with hairy cell appearance: hairy B-cell lymphoproliferative disorder]

A 72-year-old woman was referred to our hospital for evaluation of leukocytosis revealed by a medical examination. Her physical examination demonstrated no splenomegaly and no palpable lymph nodes. Her white cell count was 10,900/microl with atypical lymphocytosis (84.5%). Her hemoglobin concentration was 10.4 g/dl, and platelet count 151,000/microl. On peripheral blood smears, the atypical lymphocytes had a hairy cell-like appearance, and phase-contrast microscopic and transmission electron microscopic findings revealed the lymphocytes had many long surface microvilli. Flowcytometric analysis of peripheral blood lymphocytes identified expanded B-lymphocytes as having the IgG+, CD5- CD10- CD11c+ CD19+ CD20+ CD23- CD25- and CD103- cell surface phenotype. Serum electrophoresis disclosed polyclonal elevation of IgG and IgM (2620 mg/dl and 840 mg/dl, respectively). No light-chain restriction and a polyclonal VH gene rearrangement pattern indicated the polyclonal proliferation of B cells. The patient was a nonsmoker and had HLA-DR4, as in previous reports which have suggested an association between hairy B-cell lymphoproliferative disorder (HBLD) and HLA-DR4. No chromosome 3 abnormality was observed. These findings were consistent with the characteristics of HBLD, but differed in some respects from those of persistent polyclonal B-cell lymphocytosis (PPBL). Therefore, we diagnosed this patient as having HBLD.