NORD gratefully acknowledges the Platelet Disorder Support Association and PDSA Medical Advisor Douglas Cines, MD, for assistance in the preparation of this report.
Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by the abnormally low levels of blood cells called platelets, otherwise referred to as thrombocytopenia. Platelets are specialized blood cells that maintain the integrity of our blood vessel walls and help prevent and stop bleeding by accelerating clotting. A normal platelet count ranges from approximately 150,000 to 400,000 per microliter of blood depending on the laboratory. If someone has a platelet count lower than 100,000 per microliter of blood with no other reason for low platelets, that person has thrombocytopenia and might have ITP. There is currently no definitive laboratory test to diagnose ITP. Rather ITP is considered a diagnosis of exclusion (see below) meaning that other causes have been excluded or are unlikely.
As the platelet count falls, the risk of developing bleeding symptoms increases. Patients with ITP typically present to their doctor with abnormal bleeding into the skin resulting in bruising, or purpura. Tiny red dots on the skin, or petechiae, often appear. Bleeding from mucous membranes also may occur and may subsequently result in low levels of circulating red blood cells (anemia). Internal bleeding is less common.
ITP is called acute when it has been present for less than one year and chronic when present for longer. The clinical onset may be rapid or gradual. Eighty percent (80%) of children who present with ITP have the self-limited acute form that resolves with or without treatment (spontaneously) within 12 months and often sooner. In contrast, the proportion of adults with ITP who have a chronic condition is much higher, exceeding 50% in most series. ITP that develops in adolescents more often follows the clinical course seen in adults than what is seen in younger children.
Mechanistically, the fundamental abnormality lies in the recognition of the patient’s platelets as foreign, thereby eliciting an immune response in which B-lymphocytes make self-reactive anti-platelet antibodies that attach to the platelets. White blood cells in the spleen and in other organs, including the spleen, recognize antibody-coated particles, in this case platelets, leading to their ingestion and destruction. The bone marrow attempts to compensate but is unable to keep up with the destruction. In addition, the anti-platelet antibodies may impair platelet production as well.
While it may seem like ITP is a simple disease, there are many nuances to diagnosis and management, in addition to the variability of outcomes between children and adults, including variation in how the patients and their disease respond to various forms of treatment. Management depends on severity of symptoms, platelet count, age, lifestyle, response to therapy and its side effects, the presence of other medical issues, and, of course, personal preferences.
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