Immune Thrombocytopenia

 

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

Primary 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

First-line Therapies

  • 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.

Second-line Therapies

  • 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

Evernote: https://www.evernote.com/shard/s338/sh/7fd37bb5-3ca9-47eb-8ebd-736349692d07/360c541e53b23b9ce875a6ac8f926398

 

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