A 56-year-old man has fatigue, abdominal discomfort, and recurrent skin infections. Examination shows massive splenomegaly without lymphadenopathy. CBC: hemoglobin 9.4 g/dL, WBC 2,800/uL, neutrophils 600/uL, monocytes strikingly absent, platelets 90,000/uL. Bone marrow aspiration yields a dry tap; trephine biopsy shows interstitial infiltrates of cells with abundant cytoplasmic projections and marked reticulin fibrosis. Cytochemistry shows tartrate-resistant acid phosphatase positivity. What is the diagnosis?
- A Chronic lymphocytic leukaemia
- B Hairy cell leukaemia ✓
- C Primary myelofibrosis
- D Splenic marginal zone lymphoma
Correct answer: B. Hairy cell leukaemia
Explanation
Splenomegaly with pancytopenia, profound monocytopenia, a dry tap from reticulin fibrosis, hairy cells with cytoplasmic projections, and tartrate-resistant acid phosphatase positivity together establish hairy cell leukaemia, which responds dramatically to cladribine or pentostatin. Primary myelofibrosis gives a leukoerythroblastic smear with teardrop cells rather than monocytopenia with hairy cells, and CLL causes lymphadenopathy with mature lymphocytosis rather than pancytopenia with a dry tap.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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