Essential thrombocythemia
| Essential thrombocythaemia | |
|---|---|
 |
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| Classification and external resources | |
| Specialty | hematology |
| ICD-10 | D75.2, D47.3 |
| ICD-9-CM | 238.71 |
| ICD-O | M9962/3 |
| OMIM | 187950 |
| DiseasesDB | 4522 |
| MedlinePlus | 000543 |
| eMedicine | med/2266 |
| MeSH | D013920 |
Essential thrombocytosis (ET; also known as essential thrombocythemia, essential thrombocythaemia, primary thrombocytosis) is a rare chronic blood disorder characterised by the overproduction of platelets by megakaryocytes in the bone marrow. It may, albeit rarely, develop into acute myeloid leukaemia or myelofibrosis. It is one of four myeloproliferative disorders (disorders characterised by increased production of a particular line of blood cell).
Most people with ET are without symptoms referable to ET at the time of diagnosis, which is usually ultimately made after noting an elevated platelet level on a routine complete blood count (CBC). The most common symptoms are bleeding, blood clots, headache, nausea, vomiting, abdominal pain, visual disturbances, dizziness, fainting, and numbness in the extremities; the most common signs are increased white blood cell count, reduced red blood cell count, and enlarged spleen.
In ET, megakaryocytes are more sensitive to growth factors [citation needed]. Platelets derived from the abnormal megakaryocytes are activated, which, along with the elevated platelet count, contributes to the likelihood of thrombosis. The increased possibility of bleeding when the platelet count is over 1 million is due to von Willebrand factor (vWF) sequestration by the increased mass of platelets, leaving insufficient vWF for platelet adhesion. A mutation in the JAK2 kinase (V617F) is present in 40–50% of cases: it is diagnostic. JAK2 is a member of the Janus kinase family.
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