A 55-year-old man presents with fatigue and massive splenomegaly. CBC shows pancytopenia. Bone marrow aspiration yields a dry tap. Biopsy shows characteristic cells with hair-like cytoplasmic projections. Which specific stain is classically positive in this condition?

• A Myeloperoxidase (MPO)
• B Periodic acid-Schiff (PAS)
• C Sudan Black B
• D Tartrate-resistant acid phosphatase (TRAP) ✓

Explanation

Hairy cell leukemia is characterized by pancytopenia, massive splenomegaly, and a dry tap due to marrow fibrosis. The malignant cells stain positively for tartrate-resistant acid phosphatase. MPO and Sudan Black D are myeloid markers. PAS stains glycogen, often seen in acute lymphoblastic leukemia.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.