Immune Thrombocytopenia

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DESCRIPTION

  • Immune thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by:
    • Isolated thrombocytopenia (platelet count formally <100,000/mm3, typically <20,000/mm3)
    • Increased platelet destruction
    • Increased number of megakaryocytes in the bone marrow
  • Primary ITP implies absence of other causes or disorders that may be associated with thrombocytopenia.
  • Secondary ITP refers to immune-mediated thrombocytopenia with an underlying cause (e.g., medications, infections, autoimmune disease, immune dysregulation syndromes).
  • Phases of ITP
    • Newly diagnosed (acute) ITP: ITP within 3 months of initial diagnosis
    • Persistent ITP: ITP between 3 and 12 months from initial diagnosis
    • Chronic ITP: ITP lasting >12 months after initial diagnosis

EPIDEMIOLOGY

  • Most common acquired platelet disorder in childhood
  • Incidence is 5 to 10/100,000 children per year (<15 years of age)
  • Males and females are equally affected in childhood ITP but mild male predominance in younger children
  • Female-to-male ratio is 2:1 in adult and chronic ITP
  • Median age at diagnosis is 4 years.
  • Children aged <1 year or >10 years are more likely to develop chronic ITP.

PATHOPHYSIOLOGY

  • Thrombocytopenia due to increased destruction of antibody-coated platelets by tissue macrophages in the reticuloendothelial system, particularly the spleen
  • It is hypothesized that antibodies (usually immunoglobulin G [IgG]) generated in response to foreign antigen or medications cross-react with platelet membrane glycoproteins (most commonly IIb/IIIa and Ib/IX).
  • Other mechanisms of immune dysregulation have been implicated, including possible impaired platelet production, limiting the ability to compensate for destruction.
  • Typical bone marrow aspirate shows increased numbers of immature megakaryocytes.

COMMONLY ASSOCIATED CONDITIONS

  • ITP often follows a viral syndrome by a few weeks; this may be associated with higher likelihood of spontaneous recovery.
  • In younger children, primary ITP is the most common etiology.
  • Secondary ITP is seen with autoimmune disorders (e.g., systemic lupus erythematosus, autoimmune lymphoproliferative syndrome, common variable immunodeficiency).
  • HIV

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