Thrombocytopenia is a decrease in the circulating number of platelets (< 100,000 per microliter) in absence of toxic exposure or a disease associated with a low platelet count. It occurs as a secondary effect of peripheral platelet destruction as well as decreased platelet production. It is a diagnosis of exclusion.
Acute ITP is a common disease of childhood which usually follows an acute infection and has spontaneous resolution within 2 months. Chronic ITP is a disease which persists after 6 months without a specific cause. Usually seen in adults and persists for months to years.
ITP is caused by IgG autoantibodies on platelet surface. Risk factors include: Acute infection; Age; Cardiopulmonary bypass; Hypersplenism; Antiphospholipid antibody syndrome; Preeclampsia; and HIV infection. Over 150 drugs have been implicated in immune thrombocytopenia.
Low platelets can be caused by anemia (pernicious, aplastic, hemolytic), infections (viral, bacterial, rickettsial, malaria), exposure to DDT and other chemicals, liver disease, hyperthyroidism, and hypothyroidism.
The most common causes of immunologic thrombocytopenia are viral or bacterial infections, drugs, and a chronic autoimmune disorder referred to as idiopathic thrombocytopenic purpura (ITP). Patients with immunologic thrombocytopenia do not usually have splenomegaly and have an active bone marrow with an increased number of megakaryocytes. Most drugs induce thrombocytopenia by eliciting an immune response in which the platelet is an innocent bystander. The platelet is damaged by complement activation following the formation of drug-antibody complexes.
Decreases in platelet count have been found after ingestion of Canola oil. Marine oils, particularly cod liver oil and olive oil, caused changes in platelet membranes that are favorably antithrombotic.
Melatonin has been shown to stimulate thrombopoiesis.
Thrombocytopenia can result from an autoimmune disease triggered by the measles vaccine.
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