A 58-year-old man has progressive fatigue and abdominal fullness. Examination shows massive splenomegaly but no lymphadenopathy. CBC: hemoglobin 9.8 g/dL, WBC 3,200/μL, platelets 88,000/μL. Bone marrow aspiration yields a dry tap. Trephine biopsy shows interstitial infiltrates of medium-sized cells with abundant cytoplasmic projections and an eccentric ovoid nucleus. Which finding confirms the diagnosis?

• A Tartrate-resistant acid phosphatase positivity and CD25/CD103 expression on flow cytometry ✓
• B CD5 and CD23 co-expression with dim surface immunoglobulin
• C Presence of Philadelphia chromosome by cytogenetics
• D Reticulin fibrosis with megakaryocytic atypia and JAK2 V617F mutation

Explanation

Splenomegaly without lymphadenopathy, pancytopenia, a dry tap, and circulating cells with cytoplasmic hair-like projections indicate hairy cell leukaemia. Confirmation rests on tartrate-resistant acid phosphatase positivity and the classic immunophenotype CD11c, CD25, CD103, annexin A1. CD5/CD23 positivity identifies CLL, which presents with lymphocytosis rather than pancytopenia. Primary myelofibrosis gives a dry tap too but shows teardrop cells and JAK2 or CALR mutation, not these markers.

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.