A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 66-year-old man comes to the physician for a 3-month history of fatigue. He has hypertension and hyperlipidemia. He had a transient ischemic attack 3 years ago. He drinks 3 beers a day, and sometimes a couple more on social occasions. He currently takes aspirin, simvastatin, hydrochlorothiazide, and metoprolol. His temperature is 37.1°C (98.8°F), pulse is 78, respirations are 19/min, and oxygen saturation on room air is 97%. He is in no distress but shows marked pallor and has multiple pinpoint, red, nonblanching spots on his extremities. On palpation, his spleen is significantly enlarged. Laboratory studies show a hemoglobin of 8.0 g/dL, a leukocyte count of 80,000/mm3, and a platelet count of 34,000/mm3. A blood smear shows immature cells with large, prominent nucleoli and pink, elongated, needle-shaped cytoplasmic inclusions. Which of the following is the most likely diagnosis?
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A
Acute lymphoblastic leukemiaIncorrect. ALL is the most common pediatric leukemia; in adults it is less common, blasts are typically smaller without Auer rods, and ALL blasts express TdT/CD10 (B-ALL) — Auer rods are NOT seen.
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B
Myelodysplastic syndromeIncorrect. MDS shows cytopenias with dysplastic features and <20% blasts in marrow; a WBC of 80,000 with prominent blasts and Auer rods is overt AML, not MDS (though AML may arise FROM MDS).
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C
Chronic lymphocytic leukemiaIncorrect. CLL is a mature B-cell leukemia of older adults with smudge cells and lymphocytosis, not myeloid blasts with Auer rods.
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D
Acute myelogenous leukemiaCorrect. needle-shaped cytoplasmic inclusions are Auer rods, which are pathognomonic for AML; the older adult with marrow failure and blasts fits AML.
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E
Chronic myelogenous leukemia in blast crisisIncorrect. CML in blast crisis can produce a high WBC with blasts but is preceded by a chronic phase of marked leukocytosis with a left-shifted myeloid series and Philadelphia chromosome; Auer rods are not a feature, making de novo AML more likely.
↑ Tap an answer to reveal the reasoning
Answer: D. An older adult with pancytopenia (anemia, thrombocytopenia despite high WBC), splenomegaly, petechiae, and a blast count of 80,000/mm³ with prominent nucleoli and PINK NEEDLE-SHAPED CYTOPLASMIC INCLUSIONS has acute myeloid leukemia — specifically, the description of needle-shaped inclusions is Auer rods, which are pathognomonic for AML. Auer rods are crystallized azurophilic granules and appear as red-pink rods on Wright-Giemsa stain; they are most prominent in AML with maturation (M2) and especially in acute promyelocytic leukemia (APL/M3).
AML is the most common acute leukemia in adults (median age ~68), and presents with the consequences of bone marrow failure (anemia, thrombocytopenia, neutropenic infections) and tissue infiltration (gum hypertrophy, leukemia cutis, sometimes CNS disease). DIC is a particular concern in APL because of release of tissue factor from promyelocyte granules.
Diagnosis requires ≥20% myeloid blasts in marrow or peripheral blood, plus flow cytometry, cytogenetics, and molecular markers (FLT3, NPM1, CEBPA) for prognostication and treatment. APL (PML-RARA, t(15;17)) is treated with all-trans retinoic acid (ATRA) + arsenic trioxide; other AML subtypes are treated with "7+3" induction (cytarabine + anthracycline).
**Why each option:**
**A.** ALL is the most common pediatric leukemia; in adults it is less common, blasts are typically smaller without Auer rods, and ALL blasts express TdT/CD10 (B-ALL) — Auer rods are NOT seen.
**B.** MDS shows cytopenias with dysplastic features and <20% blasts in marrow; a WBC of 80,000 with prominent blasts and Auer rods is overt AML, not MDS (though AML may arise FROM MDS).
**C.** CLL is a mature B-cell leukemia of older adults with smudge cells and lymphocytosis, not myeloid blasts with Auer rods.
**D.** Correct — needle-shaped cytoplasmic inclusions are Auer rods, which are pathognomonic for AML; the older adult with marrow failure and blasts fits AML.