idiopathic thrombocytopenic purpura

ITP results from IgG autoantibodies directed against platelet surface glycoproteins (commonly GPIIb/IIIa), leading to opsonization and destruction of platelets by splenic macrophages via Fc receptor-mediated phagocytosis. This causes isolated thrombocytopenia without anemia or leukopenia. In children, ITP is often acute, self-limited, and follows a viral infection or vaccination, typically resolving within weeks to months. In adults, it tends to be chronic (>12 months), more common in women, and may be primary or secondary to conditions like SLE, HIV, or lymphoproliferative disorders.

Clinical features include mucocutaneous bleeding: petechiae, purpura, epistaxis, gingival bleeding, and menorrhagia. Severe bleeding (e.g., intracranial hemorrhage) is rare but more likely when platelet counts fall below 10,000-20,000/µL. Physical exam typically shows no splenomegaly (unlike other causes of thrombocytopenia).

Laboratory findings show isolated thrombocytopenia (platelet count often <100,000/µL) with normal PT/PTT, normal peripheral smear morphology (though may show large platelets/megathrombocytes reflecting increased marrow production), and normal or increased megakaryocytes on bone marrow biopsy (rarely needed for diagnosis). ITP is a diagnosis of exclusion; other causes of thrombocytopenia (drug-induced, TTP/HUS, DIC, bone marrow failure, hypersplenism) must be ruled out.

Management depends on severity and bleeding risk. Asymptomatic patients with platelets >30,000/µL may be observed. First-line treatment for symptomatic patients includes corticosteroids (e.g., prednisone) and/or IVIG (especially for rapid platelet elevation before procedures or in acute bleeding). Anti-D immunoglobulin can be used in Rh-positive, non-splenectomized patients. Refractory or chronic cases may require splenectomy, rituximab, or thrombopoietin receptor agonists (eltrombopag, romiplostim). Platelet transfusions are reserved for life-threatening bleeding since transfused platelets are also rapidly destroyed.

Key board associations: ITP is a common cause of thrombocytopenia in an otherwise healthy child following a viral illness; distinguishing from TTP (which has microangiopathic hemolytic anemia, fever, renal dysfunction, neurologic symptoms - pentad) is high-yield.