Idiopathic Thrombocytopenic Purpura

Basics

Idiopathic thrombocytopenic purpura (ITP) is thrombocytopenia without apparent cause or abnormalities in other cell lines
Incidence is ∼2–5/100,000/yr – may be an underestimate owing to undetected, subclinical cases
Acute ITP:
- 1/2 of cases involve children
- 80% of children recover within 8 wk with or without therapy
- Adult recovery is delayed and requires specific therapy to achieve remission
Chronic ITP:
- Platelets <150,000 for >6 mo following a diagnosis of ITP
- Occurs mostly in adults
- Young women are most susceptible in adult-onset ITP
- Characterized by variable response to corticosteroids and other immune suppressants
- 60–70% respond to splenectomy
Chronic refractory ITP:
- Platelet counts may often wax and wane
- Often do not respond to therapy
- No clear optimal course of treatment
Genetics:
- ITP appears to run in families, as do variations in response to corticosteroids for treatment

Autoantibodies produced by B-cells and plasma cells cause immune-mediated destruction of circulating platelets
Macrophages in spleen and liver mediate destruction of platelets via IgG autoantibodies
IgM and IgA rarely have been seen
Some patients do not possess autoantibodies, suggesting a role for T-cell–mediated cytotoxicity
C3 and C4 complements have also been shown to play a role in patients that lack autoantibodies
Poor platelet production may also play a role especially in chronic or refractory cases of ITP
Eradication of Helicobacter pylori can sometimes be associated with platelet recovery (unclear mechanism)

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