ITP

Last edited 10/2022 and last reviewed 12/2022

Immune thrombocytopaenia (ITP) (idiopathic thrombocytopaenia purpura)

• is a common hematologic disorder characterized by isolated thrombocytopenia
• ITP presents as:
  • primary form characterized by isolated thrombocytopenia (platelet count < 100 × 10^9/L) in the absence of other causes or disorders that may be associated with thrombocytopenia
  • secondary form in which immune thrombocytopenia develops in association with another disorder that is usually immune or infectious (1)

Initially known as "idiopathic thrombocytopenic purpura"

• however, an International Working Group (IWG) on ITP recently recommended that this disease be designated "Immune ThrombocytoPenia" (retaining the abbreviation ITP); this terminology recognizes the immune pathogenesis of ITP and the fact that patients with ITP may not uniformly exhibit purpura or bleeding manifestations (2)

Three distinct forms are recognised:

• term "acute ITP" has been replaced by "newly-diagnosed ITP2, which refers to ITP diagnosed within the preceding 3 months" (2)
• "persistent ITP"is designated as immune thrombocytopenia of 3-12 months duration
• "chronic ITP" is defined as disease of more than 12 months duration.

The pathogenesis of the two forms is thought to be different. The acute form is due to immune complexes; the chronic form, to specific IgG antiplatelet antibodies.

• anti-platelet glycoprotein antibodies cause thrombocytopenia through two mechanisms:
  • 1) reducing the survival of circulating platelets, and
  • 2) inhibiting the production of new platelets by bone marrow megakaryocytes

Managment:

• first line of therapy for ITP includes corticosteroids, sometimes in conjunction with IVIg or anti-Rh(D). While these are effective therapies, none reliably induce durable remission
• second line therapy for ITP may include Rituximab, splenectomy or thrombopoietin receptor agonists (TRAs)
• fostamatinib is a treatment option for chronic ITP
  • is the first spleen tyrosine kinase (Syk) inhibitor approved for the treatment of chronic immune thrombocytopenia (ITP) in adult patients who have had an insufficient response to previous treatment
  • by inhibiting Syk activation in macrophages, fostamatinib blocks autoantibody-mediated platelet phagocytosis
• splenectomy provides the greatest chance for long term remission, but its use is declining

Reference:

• Kistangari G, McCrae KR. Immune thrombocytopenia. Hematol Oncol Clin North Am. 2013 Jun;27(3):495-520.
• Rodeghiero F, Stasi R, Gernsheimer T, et al. Standardization of terminology, definitions and outcome criteria in immune thrombocytopenic purpura of adults and children: report from an international working group. Blood. 2009;113:2386-2393.
• Paik J. Fostamatinib: A Review in Chronic Immune Thrombocytopenia. Drugs. 2021 Jun;81(8):935-943.