Description

• Idiopathic thrombocytopenic purpura (ITP) is an acquired, isolated thrombocytopenia with platelet counts of <100 × 10⁹/L caused by accelerated destruction and/or impaired thrombopoiesis by antiplatelet antibodies.
• ITP is classified by:
  • Age: Adult or pediatric
  • Duration: Newly diagnosed (<3 months), persistent, or chronic (>12 months)
  • Whether it occurs in isolation or in association with other disorder: Primary (idiopathic) or secondary
• ITP is a relatively common disease of childhood that often follows viral infection or vaccination. Onset is within 1 week, and spontaneous resolution occurs within 2 months in 83% of patients.
• In adults, ITP is usually a chronic disease and spontaneous remission is rare (9% in 1 series) (1).
• System(s) affected: Heme, Lymphatic, Immunologic
• Synonym(s): Immune thrombocytopenia; Immune thrombocytopenic purpura; and Werlhof disease

Epidemiology

• Peak age:
  • Pediatric ITP: 2–4 years
  • Chronic ITP: >50
  • Uncommon in geriatric population
• Predominant gender:
  • Pediatric ITP: Male = Female
  • Chronic ITP: Female > Male (1.2–1.7:1)

Meta-analysis of 3 studies from Europe estimated incidence at:

• 1.9–6.4/100,000 children/year
• 3.3/100,000 adults/year (2)

• Based on insurance data, overall prevalence of 9.5/100,000 persons.
• Based on survey of hematologists in 2004:
  • Overall prevalence of 11.2/100,000 persons
  • In children (<16 years), 8.1/100,000 with average age of 6 years
  • In adults (>16), 12.1/100,000 persons with average age of 55 (3)

Risk Factors

• Autoimmune thrombocytopenia (e.g., Evan syndrome)
• Common variable immune deficiency
• Drug side effect (e.g., quinidine, gold, penicillin, procainamide, methyldopa, sulfamethoxazole)
• Infections: H. pylori, hepatitis C, HIV, varicella zoster
• Vaccination side effect
• Bone marrow transplantation side effect
• Connective tissue disease such as systemic lupus erythematosus, antiphospholipid antibody syndrome
• Lymphoproliferative disorders

Pathophysiology

• Accelerated platelet uptake and destruction by reticuloendothelial phagocytes results from action of IgG autoantibodies against platelet membrane glycoproteins IIb/IIIa. There is also cell-mediated platelet destruction by CD8⁺ T cells.
• Autoantibodies interfere with megakaryocyte maturation, resulting in decreased production.

Commonly Associated Conditions

• Viral infections such as measles, rubella, varicella, influenza, and EBV
• Live virus vaccinations carry a lower risk than natural viral infection: 2.6 cases per 100,000 MMR vaccine doses vs. 6–1,200 per 100,000 cases of natural rubella or measles infections