A 58-year-old man has pancytopenia and moderate splenomegaly. Bone marrow aspiration yields a dry tap. Peripheral smear shows mononuclear cells with abundant cytoplasm and hair-like villous projections. The diagnostic cytochemical stain is:

• A Tartrate-resistant acid phosphatase ✓
• B Myeloperoxidase
• C Periodic acid-Schiff
• D Leucocyte alkaline phosphatase

Explanation

Hair-like cytoplasmic projections with a dry tap from marrow fibrosis and splenomegaly are classic for hairy cell leukaemia, whose neoplastic B cells characteristically stain tartrate-resistant acid phosphatase positive; flow shows CD11c, CD25 and annexin A1 positivity. Myeloperoxidase marks myeloid lineage blasts, PAS is used in some ALL and erythroleukaemia, and raised leucocyte alkaline phosphatase score belongs to polycythaemia vera, not a B-cell neoplasm.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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