A 4-year-old boy has appeared listless during the past week. He exhibits irritability when his arms or legs are touched. In the past 2 days, large ecchymoses have appeared on the right thigh and left shoulder. CBC shows hemoglobin, 9.3 g/dL; hematocrit, 28.7%; MCV, 96 mm3; platelet count, 45,000/mm3; and WBC count, 13,990/mm3. Examination of the peripheral blood smear shows blasts that lack peroxidase positive granules, but contain PAS-positive aggregates and stain positively for deoxynucleotidyl transferase negative (TdT-). Flow cytometry shows the phenotype of blasts to be CD19+, CD3-, and sIg-. Which of the following is the most likely diagnosis?
A 4-year-old boy has appeared listless during the past week. He exhibits irritability when his arms or legs are touched. In the past 2 days, large ecchymoses have appeared on the right thigh and left shoulder. CBC shows hemoglobin, 9.3 g/dL; hematocrit, 28.7%; MCV, 96 mm3; platelet count, 45,000/mm3; and WBC count, 13,990/mm3. Examination of the peripheral blood smear shows blasts that lack peroxidase positive granules, but contain PAS-positive aggregates and stain positively for deoxynucleotidyl transferase negative (TdT-). Flow cytometry shows the phenotype of blasts to be CD19+, CD3-, and sIg-. Which of the following is the most likely diagnosis?
💡 Explanation
**Core Concept**
The case describes a child presenting with symptoms of anemia, thrombocytopenia, and a high WBC count, along with specific findings on the peripheral blood smear and flow cytometry. The presence of blasts lacking peroxidase-positive granules, but containing PAS-positive aggregates and staining positively for TdT, suggests a diagnosis of acute leukemia. The specific immunophenotype of the blasts, including CD19+ and CD3-, is crucial for distinguishing between different types of leukemia.
**Why the Correct Answer is Right**
The findings of CD19+, CD3-, and sIg- blasts are characteristic of B-cell acute lymphoblastic leukemia (B-ALL). CD19 is a marker of B-cell lineage, while CD3 is a marker of T-cell lineage. The presence of sIg- (surface immunoglobulin) indicates that the B-cells are immature and have not yet undergone terminal differentiation. The blasts' lack of peroxidase-positive granules and PAS-positive aggregates are also consistent with a diagnosis of B-ALL. The symptoms and laboratory findings, including anemia, thrombocytopenia, and a high WBC count, are also typical of leukemia.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely incorrect because it does not provide a specific diagnosis. Without more information, it is difficult to determine what this option is trying to suggest.
* **Option B:** This option may be incorrect because it does not match the immunophenotype of the blasts described in the case. T-cell acute lymphoblastic leukemia (T-ALL) typically expresses CD3 and lacks CD19.
* **Option C:** This option may be incorrect because it does not match the symptoms and laboratory findings described in the case. Acute myeloid leukemia (AML) typically presents with different symptoms and laboratory findings, such as a higher platelet count and a different immunophenotype.
**Clinical Pearl / High-Yield Fact**
In pediatric patients presenting with symptoms of leukemia, it is essential to perform flow cytometry to determine the immunophenotype of the blasts. This can help distinguish between different types of leukemia and guide treatment decisions.
**Correct Answer:** B. B-cell acute lymphoblastic leukemia (B-ALL).
✓ Correct Answer: A. Acute lymphoblastic leukemia
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