A 9-year-old girl develops widespread pinpoint skin hemorrhages. She recovered from a flu-like illness 1 week earlier. Laboratory findings reveal a platelet count of 20,000/mL but no other abnormalities. Her bone marrow shows an increased number of megakaryocytes. The platelet count is normal after 2 months. Which of the following is the appropriate diagnosis?

ITP is a quantitative disorder of platelets caused by antibodies directed against platelet or megakaryocytic antigens. Similar to autoimmune hemolytic anemia, the etiology of ITP is related to antibody-mediated immune destruction of platelets or their precursors. In adults with acute ITP, the platelet count is typically less than 20,000/mL. In chronic adult ITP, the platelet count varies from a few thousand to 100,000/mL. The peripheral blood smear in ITP exhibits numerous large platelets, and the bone marrow shows a compensatory increase in megakaryocytes. Acute ITP in children typically appears after a viral illness and presents with sudden onset of petechiae and purpura without other symptoms. Spontaneous recovery can be expected in more than 80% of cases within 6 months. Thrombocytopenia may be observed in the other choices but is usually associated with other systemic signs and symptoms.Diagnosis: Idiopathic thrombocytopenic purpura