Question: Blood & Immune Systems
A 5-year-old boy who recently recovered from an upper respiratory tract infection develops scattered petechiae and easy bruising. He is otherwise well. Physical examination shows no hepatosplenomegaly or lymphadenopathy. Laboratory studies show a normal hemoglobin and leukocyte count with a platelet count of 18,000/mm3. A peripheral smear shows occasional large platelets and normal erythrocyte morphology. Which of the following is the most likely mechanism of the thrombocytopenia?
| Platelet count | 18,000 /mm3 |
|---|---|
| Hemoglobin | 12.5 g/dL |
Choose one answer.
Explanation
Correct answer: B. Immune-mediated destruction of platelets
Isolated thrombocytopenia with large platelets in an otherwise well child after a viral illness, with no organomegaly or other cytopenias, is immune thrombocytopenic purpura. Antiplatelet antibodies (often against GpIIb/IIIa) lead to splenic destruction of platelets, while the marrow compensates with increased megakaryocytes, producing the large platelets seen on smear. Consumptive microthrombi describe DIC or TTP, which would alter other lines; marrow replacement would cause additional cytopenias and abnormal cells.
Learning objective: Identify immune thrombocytopenic purpura from isolated post-viral thrombocytopenia.
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