Description

• Immune thrombocytopenia (ITP) is a condition characterized by the immunologic destruction of normal platelets and/or impaired thrombopoiesis in response to an unknown stimulus.
• ITP is defined as a 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 when it presents in isolation; secondary when associated with other disorders
• ITP is a relatively 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 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; in one population (in Oklahoma): Overall prevalence of 11.2/100,000 persons

Etiology and Pathophysiology

• Accelerated platelet uptake and 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 CD8⁺ T cells.
• Autoantibodies interfere with megakaryocyte maturation, resulting in 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
• Vaccination side effect. 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.
• Bone marrow transplantation side effect
• Connective tissue disease, such as: systemic lupus erythematosus, antiphospholipid antibody syndrome
• Lymphoproliferative disorders