Snapshot A 50-year-old man presents to his primary care physician for an annual visit. He has no complaints. His past medical history includes hypertension, hypercholesterolemia, and rheumatoid arthritis. He goes for routine blood tests today, which reveals marked pancytopenia. A peripheral blood smear is done, showing cells with hair-like projections. Introduction Indolent leukemia of mature B-cells with infiltration of bone marrow and spleen Epidemiology median onset 50-55 years of age male > female 4.5x Associated conditions autoimmune conditions Characteristics “hairy cells” with filamentous, hair-like projections tartrate-resistant acid phosphatase (TRAP) + Prognosis good prognosis, especially with good response to purine analogs Presentation Symptoms pancytopenia from infiltration of bone marrow fatigue infections bleeding anemia Physical exam splenomegaly from infiltration of spleen no lymphadenopathy Evaluation Peripheral blood smear B-cells with hairy projections + TRAP stain (tartrate-resistant acid phosphatase) Flow cytometry CD11c+ and CD2+ CD5- and CD10- Bone marrow aspirate dry tap due to marrow fibrosis CBC anemia thrombocytopenia leukopenia Differential Diagnosis Non-Hodgkin lymphoma Mantle cell lymphoma Treatment Purine analogs first line: cladribine (2-CDA) pentostatin both inhibit adenosine deaminase recall this is the same enzyme deficiency seen in SCID leading to B-cell dysfunction Complications Complications infections increased risk of malignancy