Idiopathic thrombocytopenic purpura pathophysiology

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increased platelet destructionEditor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

AITP is characterized by the production of autoreactive antibodies against one's own platelets, resulting in increased platelet destruction by RES phagocytes

Pathophysiology

Pathogenesis

Acute ITP: Mainly affects children and usually follows a viral or bacterial infection

• Antigenic mimicry - Similar molecular structures on both host cells and infectious agents, inducing a self immune response which cross reacts with the host antigens.
  • In acute ITP - anti-viral or anti-bacterial antibodies cross reacts against the patient's platelets.
• Mostly acute ITP is self resolving as infectious agents and antibodies are cleared from the body, causing the loss of anti-platelet reactivity.
• T cells are not involved in the parthenogenesis of acute ITP

Chronic AITP: (platelet counts < 150,000 x 10⁹ per liter x 6 months) usually in adults

• Increased platelet destruction:
  • Autoantibody‐induced platelet destruction
    • Abnormal IgG auto-antibody recognizes glycoprotein IIb/IIIa, glycoprotein Ib/IX complex, GP Ia/IIa, and GP VI etc
    • majority of these autoantibodies are IgG, but IgM and IgA can also be identified in some patients with AITP
    • Predominantly IgG auto-antibodies constitute the majority of antibodies but IgM and IgA antibodies can also be found in some of ITP patients.
    • Auto-antibodis binds to the circulating platelet membranes through glycoproteins
    • Autoantibody-coated platelets induce Fcg receptors and bind to antigen-presenting cells (Splenic macrophages or dendritic cells) in the reticuloendothelial system
    • The autoantibody-coated platelets undergo phagocytosis by splenic macrophages and peripheral blood neutrophils.
  • Autoreactive T lymphocyte‐mediated platelet lysis
    • Abnormal cytotoxic T cells defect leads to differentiation of direct autoreactive B cells further leading to secretion of IgG auto-antibodies.
    • CD4-positive helper T cells react with platelet surface glycoproteins, through co-stimulation involving CD40:CD40L
    • T cells act directly on the megakaryocytes in the bone marrow
• Autoantibody‐mediated suppression of platelet production:
  • Decreased platelet turnover
  • Abnormal thrombopoiesis
  • Autoantibody‐induced suppression of megakaryocytopoiesis
  • Megakaryocitic nuclei and cytoplasm shows degenrative changes

Associated Conditions

Conditions associated with

Gross Pathology

On gross pathology, characteristic findings of itp include:

• Acute
• Chronic

Microscopic Pathology

On microscopic histopathological analysis, characteristic findings of itp include:

• Acute
• Chronic