A 28-year-old woman presents with mucosal bleeding, petechiae, and thrombocytopenia following a viral illness. Peripheral smear shows large platelets. Bone marrow biopsy reveals increased megakaryocytes. Anti-platelet antibodies (IgG) directed against GPIIb/IIIa are detected. Which mechanism explains the thrombocytopenia?

• A Antibodies prevent platelet production from megakaryocytes
• B IgG-coated platelets are phagocytosed by splenic macrophages (Fc receptor-mediated clearance) ✓
• C Antibodies activate complement causing intravascular platelet lysis
• D Antibodies block von Willebrand factor, preventing platelet adhesion

Explanation

In immune thrombocytopenic purpura (ITP), IgG autoantibodies bind platelet surface glycoproteins (most commonly GPIIb/IIIa and GPIb/IX). The Fc portions of these antibodies are recognized by Fc gamma receptors on splenic macrophages, leading to phagocytosis and destruction of opsonized platelets — the predominant mechanism of platelet clearance. Megakaryocytes are increased (reactive) in the marrow. Complement-mediated lysis plays a minor role. Antibody-blocked megakaryocytes also reduce platelet production but are secondary.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.