ITP is the most common cause of thrombocytopenia. Other common causes include certain infections, cirrhosis, and drug-induced thrombocytopenia caused by drugs such as NSAIDs and certain antiplatelet drugs.
GPIIb/IIIa is one of the glycoproteins present on platelet membranes. Recall that it is also the receptor on platelet membranes that interacts with Von Willebrand Factor and aids in platelet activation. The pathogenesis of ITP is thought to be related to an autoimmune response against GPIIb/IIIa mediated by IgG antibodies.
The acute form of ITP is most commonly seen in otherwise well-appearing and healthy children and adolescents following a viral infection. It has also been doccumented to occasionally occur following measles, mumps, and rubella (MMR) vaccination.
The chronic form of ITP typically arises in women of childbearing age. It may be primary, meaning it occurs in isolation without any other linked conditions that may contribute to the underlying cause, or secondary, meaning it occurs in relation to known autoimmune diseases such as systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APLS).
Patients with ITP who are symptomatic may experienced prolonged bleeding. Some examples include gingival bleeding while brushing teeth, frequent or prolonged nosebleeds, and prolonged menstrual bleeding.
Patients with ITP may develop a petechial rash. Petechiae are pinpoint, round spots that appear on the skin due to bleeding in small capillaries. They typically do not loose color when pressure is applied (IE they are non-blanching) and are flat to the touch.
Patients with ITP will have an isolated decrease in platelets, while the white blood cell count and hemoglobin remain relatively within normal limits. This is in contrast to other hemotologic disorders such as hemotologic malignancies and microangiopathic hemolytic anemias in which multiple cell lines will be affected in addition to platelets.
Increased megakaryocytes may be found on bone marrow biopsy. Recall megakaryocytes are the progenitor cell to platelets, and therefore systemic destruction of platelets will result in increased production of new platelets to compensate.
ITP can be diagnosed when other causes of thrombocytopenia, such as inherited and drug-induced causes, have been ruled out. For example, low cell counts in other cell lines should warrant investigation into other causes such as malignancy or hemolytic anemias. Testing for specific antibodies is not recommended under current guidelines.
Corticosteroids are appropriate if only a short period of treatment is required, such as in patients with acute ITP that subsequently resolves. Corticosteroids help manage ITP by suppressing the immune system and therefore suppressing the autoimmune response thought to play a pathogenic role in ITP.
Administration of IVIG is sometimes indicated in patients with ITP, especially if they have extremely low platelet counts (30,000), are experiencing severe bleeding, or are unable to tolerate glucocorticoids. IVIG is sufficiently effective that it can raise the platelet count within 24-48 hours, and this effect typically persists for 2-6 weeks. IVIG acts by interfering with macrophage uptake of autoantibody-coated platelets, effectively acting as a decoy in this way.
In symptomatic patients with thrombocytopenia that is refractory to other treatment options, splenectomy may be necessary. This is thought to help because the spleen plays a role in the elimination and consumption of platelets, and therefore splenectomy can help mitigate this effect.
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