Bone marrow aspirate from a child with acute leukemia shows blasts that are negative for myeloperoxidase and Sudan black B. Which additional finding best supports a lymphoid rather than myeloid lineage?
- A Positivity for nonspecific esterase inhibited by fluoride
- B Block-like positivity with periodic acid-Schiff (PAS) stain ✓
- C Presence of Auer rods on Wright-Giemsa stain
- D Diffuse granular staining for chloroacetate esterase
Correct answer: B. Block-like positivity with periodic acid-Schiff (PAS) stain
Explanation
Lymphoblasts show coarse block-like PAS positivity resulting from glycogen accumulation, along with TdT positivity, supporting lymphoblastic leukemia. Nonspecific esterase inhibited by fluoride marks monocytic differentiation, chloroacetate esterase marks granulocytic cells, and Auer rods are pathognomonic of myeloid lineage. Any of these three findings would argue against, not for, a lymphoid origin of the blasts.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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