About ET

Essential thrombocytosis (ET, also known as essential thrombocythemia) is a rare chronic blood disorder characterized by the overproduction of platelets by megakaryocytes in the bone marrow in the absence of an alternative cause. In some cases this disorder may be progressive, and rarely may evolve into acute myeloid leukemia or myelofibrosis. It is one of four myeloproliferative disorders.

Essential thrombocytosis (primary thrombocythemia), first described by Epstein and Goedel in 1934, is a nonreactive, chronic myeloproliferative disorder.1 Essential thrombocytosis (primary thrombocythemia) is associated with sustained megakaryocyte proliferation that increases the number of circulating platelets. Traditionally, essential thrombocytosis (primary thrombocythemia) was considered a clonal disorder that involved pluripotent stem cells; however, studies have indicated that some patients may have polyclonal hematopoiesis.

Essential thrombocythemia is a stem cell disease; “essential” means that the cause is unknown. Blood cells, including red blood cells (which carry oxygen from the lungs to the rest of the body), white blood cells (which fight infections) and platelets (which form blood clots) are produced from stem cells in the bone marrow. The stem cells grow and divide into intermediate cells and finally into mature cells in the blood. A problem with the stem cell can lead to problems with all other cells. ET is a stem cell disease that leads to an overproduction of platelets (thrombocytes) without other secondary causes, sometimes with an accompanying increase in white blood cells.

Blood platelets help prevent and control bleeding resulting from injury to blood vessels. The term thrombocythemia refers to an unusually high platelet count. A normal count ranges from 150,000 to 450,000 platelets per microliter (mL) of blood. When the platelet count exceeds 600,000 platelets per mL, doctors call this essential thrombocythemia. Most young people with essential thrombocythemia have no signs or symptoms.

Essential thrombocytosis (primary thrombocythemia) is characterized by a platelet count greater than 600,000/µL, megakaryocytic hyperplasia, splenomegaly, and a clinical course complicated by thrombotic and/or hemorrhagic episodes.

ET is classified as a chronic myeloproliferative disorder (CMPD). The CMPDs also include polycythemia vera, agnogenic myeloid metaplasia with myelofibrosis, and chronic myelogenous leukemia.



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