A 26-year-old man presents with gingival swelling and bleeding. CBC: Hb 8.4 g/dL, WBC 52,000/μL with 65% large mononuclear blasts having folded, lobulated nuclei and abundant grey cytoplasm containing fine azurophilic granules, platelets 44,000/μL. Blasts are nonspecific esterase positive and lysozyme levels are elevated. Which subtype of AML is this?

• A Acute monoblastic/monocytic leukaemia (M5) ✓
• B Acute myelomonocytic leukaemia (M4)
• C Acute megakaryoblastic leukaemia (M7)
• D Acute erythroid leukaemia (M6)

Explanation

Gingival hypertrophy, tissue infiltration, folded monoblast nuclei, nonspecific esterase positivity and high lysozyme define acute monocytic leukaemia, FAB M5, commonest in young adults. M4 requires at least 20% of the nonerythroid component to be granulocytic alongside monocytic cells, so it is not supported here. Megakaryoblasts are smaller with cytoplasmic blebs and platelet markers such as CD41, while M6 is dominated by erythroid precursors, neither matching this picture.

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.