Paper I
Question
Immune Thrombocytopenia Purpura
Answer
Immune thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by isolated thrombocytopenia from antibody-mediated platelet destruction.
Pathogenesis
- Autoantibodies (usually IgG) are directed against platelet surface glycoproteins (commonly GpIIb/IIIa)
- Antibody-coated platelets are recognized and prematurely destroyed by splenic macrophages (Fc receptor-mediated phagocytosis)
- In some cases, antibodies also impair megakaryocyte function, contributing to reduced platelet production
Types
- Acute ITP: Common in children, often follows a viral infection, usually self-limiting (resolves within weeks to months)
- Chronic ITP: More common in adults (especially women), insidious onset, persists >12 months
Clinical features
- Mucocutaneous bleeding manifestations — petechiae, purpura, epistaxis, gum bleeding, menorrhagia
- Spleen typically not palpable/enlarged (unlike other causes of thrombocytopenia with splenic sequestration)
Laboratory findings
- Isolated thrombocytopenia (other cell lines normal)
- Peripheral smear: reduced platelet numbers, may show large platelets (megathrombocytes) reflecting increased marrow turnover
- Bone marrow: normal or increased megakaryocytes (compensatory response to peripheral destruction)
- Bleeding time prolonged; PT/aPTT normal (a diagnosis of exclusion, since specific antiplatelet antibody testing is not routinely required)
Treatment
- Corticosteroids (first-line)
- IV immunoglobulin (rapid platelet rise, e.g., before surgery or in severe bleeding)
- Splenectomy (chronic/refractory cases)
- Thrombopoietin receptor agonists (refractory cases)