Immune Thrombocytopenic Purpura
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- 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
- Increased number of megakaryocytes in the bone marrow
- Primary ITP implies absence of other causes for thrombocytopenia; it often follows a viral infection.
- Secondary ITP indicates other immune dysregulation associated with thrombocytopenia.
- Phases of ITP
- Newly diagnosed (acute) ITP: within 3 months of initial diagnosis
- Persistent ITP: transient improvement or continued thrombocytopenia for 3 to 12 months
- Chronic ITP: persistent thrombocytopenia >12 months after initial presentation
- Most common acquired platelet disorder in childhood
- Incidence is 5/100,000 children per year (<15 years of age).
- 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 but 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 months.
- Risk of severe bleeding is <5% and of intracranial bleeding is <0.5%.
- 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]).