<s>[INST] context: In children, ITP is the most common form of thrombocytopenic purpura. In most cases, a preceding viral infection can be noted. No diagnostic test identifies this disease; exclusion of the other diseases listed in the question is necessary. In this disease, the platelet count is frequently less than 20,000/mL, but other laboratory tests yield essentially normal results, including the bone marrow aspiration (if done). Complications are uncommon; significant bleeding occurs in only 5% of cases and intracranial hemorrhage is even rarer. The treatment of childhood ITP is controversial. Patients with mild symptoms such as bruising and self-limited epistaxis may be observed, while patients with significant bleeding should be treated. IVIG and corticosteroids are effective in causing a rapid increase in platelet count, but controversy exists surrounding the use of prednisone before ruling out leukemia with a bone marrow aspirate. For Rh-positive patients with a working spleen, the use of anti-D immunoglobulin also results in an increase in platelet count. For patients with chronic (> 1 year) ITP, a splenectomy may be necessary.Aplastic anemia is unlikely if the other cell lines are normal. vWD might be expected to present with bleeding and not just bruising. It is unlikely that acute leukemia would present with thrombocytopenia only. Thrombotic thrombocytopenic purpura is rare in children. [/INST] question: Two weeks after a viral syndrome, a 2-year-old child develops bruising and generalized petechiae, more prominent over the legs. No hepatosplenomegaly or lymph node enlargement is noted. The examination is otherwise unremarkable. Laboratory testing shows the patient to have a normal hemoglobin, hematocrit, and white blood cell (WBC) count and differential. The platelet count is 15,000/mL. Which of the following is the most likely diagnosis? | options: A: Von Willebrand disease (vWD) B: Acute leukemia C: Idiopathic (immune) thrombocytopenic purpura (ITP) D: Aplastic anemia | answer: C </s>