Immune Thrombocytopenia

Immune thrombocytopenia (ITP), formerly idiopathic thrombocytopenic purpura, is a condition arising from immunoglobulin G (IgG) autoantibodies sensitizing circulating platelets, manifesting as a low platelet count, purpura, and hemorrhagic episodes. The diagnosis is typically made by excluding known thrombocytopenia causes. ITP can affect both children and adults. The American Society of Hematology (ASH) defines ITP as a generalized purpuric rash accompanied by a platelet count less than 100,000/μL and normal white blood cell (WBC) count and hemoglobin level. Leukocyte count and hemoglobin abnormalities are not characteristic of ITP and should prompt additional diagnostic testing when detected. (American Society of Hematology)

Primary ITP develops without an underlying cause and must be distinguished from secondary ITP. Conditions that may trigger secondary ITP include drug reactions, autoimmune illnesses like systemic lupus erythematosus (SLE), malignancies like chronic lymphocytic leukemia (CLL), and infections like HIV. Primary ITP may be further categorized based on the timing and persistence of symptoms. Newly diagnosed ITP refers to the condition from the time of diagnosis to 3 months afterward. Persistent ITP arises when symptoms continue 3 to 12 months following the initial diagnosis. Chronic ITP indicates ongoing symptoms beyond 12 months from the initial diagnosis until resolution or further management. Refractory ITP includes cases that do not resolve with splenectomy.

Severe ITP, when platelet counts are below 20,000/μL, warrants medical treatment. Immunosuppressive therapy is the cornerstone of management.

Platelet Physiology

Platelets are essential for hemostasis. These blood cells originate from megakaryocytes in the bone marrow through a process called "thrombopoiesis." Under normal conditions, platelets circulating in the blood range from 150,000 to 350,000 per μL and have a mean life span of 7 to 10 days. Thrombopoietin (TPO), a hormone primarily produced in the liver, kidneys, and bone marrow, regulates platelet production by stimulating megakaryocyte proliferation and differentiation. Factors such as infection, inflammation, and hemorrhage can induce platelet proliferation to maintain normal platelet counts.

Platelets possess distinctive cellular characteristics, including a discoid shape, a lack of nuclei, and abundant granules containing clotting factors and inflammatory mediators. Glycoprotein IIb/IIIa (GP IIb/IIIa) is a key receptor on platelet membranes essential for aggregation, facilitating blood clot formation. This receptor's activation and subsequent fibrinogen binding are crucial steps in hemostasis. The spleen plays a crucial role in platelet homeostasis by removing aged or damaged platelets from circulation.