Immune Thrombocytopenia (ITP)

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DESCRIPTION

  • Immune thrombocytopenia (ITP) is a condition characterized by the destruction of normal platelets due to auto-antibodies against platelet antigens and/or impaired thrombopoiesis in response to an unknown stimulus.
  • ITP is defined as platelet count <100 × 109/L, once other causes of thrombocytopenia have been ruled out (1).
  • ITP nomenclature:
    • Newly diagnosed (<3 months), persistent (3 to 12 months), and chronic (>12 months)
    • Primary ITP due to autoimmune mechanisms, due to platelet destruction, and/or platelet underproduction with no other cause
    • Secondary ITP is caused by other disorders.
    • Drug-induced ITP caused drug dependent platelet antibodies that cause platelet destruction
  • ITP is a common disease of childhood that typically follows a viral infection. Onset is within 1 week, and spontaneous resolution occurs within 2 months in >80% of patients.
  • In adults, ITP is usually a chronic disease and spontaneous remission is rare.
  • Synonym(s): idiopathic thrombocytopenic purpura; immune thrombocytopenic purpura; and Werlhof disease

EPIDEMIOLOGY

  • Peak age: pediatric ITP: 2 to 4 years; chronic ITP: >50 years with incidence 2 times higher in persons aged 60 years than those <60 years of age
  • Predominant gender: pediatric ITP: male = female; chronic ITP: female > male (1.2 to 1.7:1)

Incidence

  • Pediatric acute ITP: 1.9 to 6.4/100,000 children per year; adult ITP: 1.6/100,000 per year (1)
  • Peak incidence of ITP is in the spring and early summer in temperate climates. This observation supports the notion that viral triggers are an important cause of ITP.

Prevalence

Limited data; 12/100,000 persons

ETIOLOGY AND PATHOPHYSIOLOGY

  • Infection/immune changes are the most common cause of ITP.
  • Accelerated platelet uptake/destruction by reticuloendothelial phagocytes results from action of IgG autoantibodies against platelet membrane glycoproteins IIb/IIIa, GP Ib/IX, GP Ia/IIa, and GP VI. There is also cell-mediated platelet destruction by autoreactive cytotoxic T cells.
  • Humoral and cellular immunity interfere with megakaryocyte maturation, causing decreased production.
  • Fc-independent desialylated platelet clearance has been proposed as the mechanism of refractoriness to therapies that target the classic FC-dependent pathway.
  • Association in patients receiving immune checkpoint inhibitor therapy

RISK FACTORS

  • Autoimmune thrombocytopenia (e.g., Evans syndrome)
  • Common variable immunodeficiency (CVID)
  • Drug side effect (e.g., quinidine, vancomycin, penicillin, sulfonamides)
  • Infections: Helicobacter pylori, hepatitis C, HIV, CMV, varicella zoster, measles, rubella, influenza, EBV, Whipple disease
  • Vaccinations: Live virus vaccinations carry a lower risk than natural viral infection: 2.6/100,000 cases MMR vaccine doses versus 6 to 1,200/100,000 cases of natural rubella or measles infections. Vaccine-induced immune thrombotic thrombocytopenia (VITT) is more like autoimmune heparin-induced thrombocytopenia (HIT) than ITP.
  • Bone marrow transplantation
  • Autoimmune disease, such as systemic lupus erythematosus, antiphospholipid antibody syndrome
  • Lymphoproliferative disorders

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