Immune Thrombocytopenia (ITP)
- Remember, diagnosis of ITP is one of exclusion. Before diagnosing someone with immune thrombocytopenia, consider other non-immune causes of thrombocytopenia: ex) drugs, chronic liver disease, hypersplenism, transient myelosuppression due to infection, pregnancy (gestational thrombocytopenia or pregnancy-associated microangiopathic syndromes)
- Think of ITP in terms of primary (idiopathic) versus secondary (associated with another condition)
Classification of ITP
- Acquired thrombocytopenia due to autoimmune platelet destruction that is NOT triggered by an associated condition.
Secondary ITP (immune mediated process associated with another condition)
- Infections: HIV, HCV
- Rheumatologic: SLE
- Malignancy: CLL
- Drug induced: lots of drugs can do this! : Amiodarone, Beta-lactam antibiotics, Carbamazepine, Linezolid, MMR vaccine, Phenytoin, Quinidine, Quinine, Vancomycin
Treatment of ITP
- IVIG: Works more rapidly than steroids! : Initial response in platelet count can be seen as early as 1-3 days à so used preferentially as first agent in patients with: active bleeding, urgent procedural needs,
- Glucocorticoids: Response rates at 1 year are similar to that those of IVIG, but slower onset in increasing platelet count than IVIG (takes about 3-5 days)
- Anti-D (RhoGAM): Alternative to IVIG for patients whose RBCs are Rh(D) positive : immune globulin directed against D antigen of Rh system à thought to raise platelet count by saturating macrophage Fc receptors with anti-D-coated RBCs.
- Splenectomy: Removes major site of phagocytosis of anti-body coated platelets : platelet counts typically rise within first 2 weeks post-operatively : Used in patients who require additional therapy beyond IVIG or glucocorticoids.
- Rituximab: Monoclonal antibody against B cell surface protein CD 20 à eliminates B cells via apoptosis : Beware of side effects – reactivation of HBV, PML (rare), infusion-related reactions, may interfere with immunizations (immunize patients before initiating rituximab!)
What about those Thrombopoietin Receptor Agonists?
- In today’s case, our patient was started on a thrombopoietin receptor agonist, which brings up interesting discussions on their indications and side effects.
- Thrombopoietin (TPO) receptor agonists, aka “TPO mimetics” should only be reserved for patients with severe and symptomatic thrombocytopenia who have failed the aforementioned first line and second line therapies.
- Available agents:
- Romiplostim (Nplate): once-weekly SQ injection
- Eltrombopag (Promacta, Revolade): once daily pill
- EXTEND study: Evaluated the long-term efficacy of eltrombopag : Followed 299 patients treated for up to 3 years : Responses seen in 80-88% of patients with and without splenectomy : ~50% of patients remained on eltrombopag at the time of publication.
- Side Effects:
- Risk of thrombosis: Although agents have been associated with increased risk of thrombosis in certain patient populations, a 2015 meta-analysis did not suggest this risk in the subgroup of patients with ITP
- Increased BM reticulin formation
- Headache, GI upset, transaminitis