Idiopathic Thrombocytopenic Purpura

Basics

Description

  • Idiopathic or immune thrombocytopenic purpura (ITP) is an autoimmune syndrome characterized by the following:
    • Isolated thrombocytopenia (platelet count formally <100,000/mm3, typically <20,000/mm3)
    • Shortened platelet survival
    • Platelet autoantibodies
    • Increased number of megakaryocytes in the bone marrow
  • Primary ITP implies absence of other causes for thrombocytopenia; secondary ITP indicates another diagnosis associated with autoimmune thrombocytopenia.
  • Phases of ITP
    • Newly diagnosed (acute) ITP: within 3 months of initial diagnosis
    • Persistent ITP: transient improvement or continued thrombocytopenia for 3–12 months
    • Chronic ITP: persistent thrombocytopenia >12 months after initial presentation

Epidemiology

  • Most common acquired platelet disorder in childhood
  • Often follows viral syndrome by a few weeks; this may be associated with higher likelihood of spontaneous recovery.
  • Males and females are equally affected in childhood ITP (mild male predominance in younger children; female-to-male ratio is 3:1 in adult and chronic ITP).
  • Median age at diagnosis is 4 years. Children <1 year or >10 years are more likely to develop chronic ITP.
  • >70% of childhood ITP resolves within 6–12 months.
  • Risk of severe bleeding is <5% and of intracranial bleeding is ∼0.5%.

Incidence

Incidence is 1–10/100,000 children per year (<15 years of age).

Pathophysiology

  • Thrombocytopenia due to increased destruction of antibody-coated platelets in the reticuloendothelial system, particularly the spleen
  • Hypothesized that antibodies generated in response to foreign antigen or drug cross-react with platelet membrane glycoproteins (most commonly IIb/IIIa and Ib/IX)
  • Other mechanisms of immune dysregulation have been implicated, including possible inhibition of thrombocytopoiesis, limiting ability to compensate for destruction.
  • Typical bone marrow aspirate shows increased numbers of immature megakaryocytes.

Commonly Associated Conditions

  • In younger children, primary ITP is the most common presentation of ITP.
  • Secondary ITP is seen with autoimmune disorders (e.g., systemic lupus erythematosus [SLE], autoimmune lymphoproliferative syndrome [ALPS]).
  • HIV

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