Synonyms
Essential hemorrhagic thrombocythemia; Idiopathic thrombocythemia; Primary thrombocythemia
Definition
Essential thrombocythemia (ET) is a subtype in the group of chronic myeloproliferative neoplasms (MPN) and usually defined by a marked and sustained thrombocytosis. The platelets often display anisocytosis, ranging from tiny forms to atypical large, giant platelets that may reveal bizarre shapes, pseudopods, and agranularity. The WBC count and leukocyte differential are usually normal, although a borderline elevation in the neutrophil lineage may occur. Even in prodromal stages of ET, relevant complications (i.e., hemorrhage, vascular events) have been described. These patients presented with a persistent platelet count lower than the threshold value of 450 × 109/L required to meet the diagnostic criteria of the WHO but reveal corresponding driver mutations (JAK2, CALR, MPL) in most cases and clearly demonstrate a characteristic BM morphology (Table 1).
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References and Further Reading
Arber, D. A., Orazi, A., Hasserjian, R., Thiele, J., Borowitz, M. J., Le Beau, M. M., et al. (2016). The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood, 127(20), 2391–2405.
Barbui, T., Thiele, J., Carobbio, A., Guglielmelli, P., Rambaldi, A., Vannucchi, A. M., et al. (2014). Discriminating between essential thrombocythemia and masked polycythemia vera in JAK2 mutated patients. American Journal of Hematology, 89(6), 588–590.
Barbui, T., Thiele, J., Carobbio, A., Vannucchi, A. M., & Tefferi, A. (2015). The rate of transformation from JAK2-mutated ET to PV is influenced by an accurate WHO-defined clinico-morphological diagnosis. Leukemia, 29(4), 992–993.
Barosi, G. (2014). Essential thrombocythemia vs. early/prefibrotic myelofibrosis: Why does it matter. Best Practice & Research. Clinical Haematology, 27(2), 129–140.
Ejerblad, E., Kvasnicka, H. M., Thiele, J., Andreasson, B., Bjorkholm, M., Lofvenberg, E., et al. (2013). Diagnosis according to World Health Organization determines the long-term prognosis in patients with myeloproliferative neoplasms treated with anagrelide: Results of a prospective long-term follow-up. Hematology, 18(1), 8–13.
Kvasnicka, H. M., & Thiele, J. (2007). Classification of Ph-negative chronic myeloproliferative disorders – Morphology as the yardstick of classification. Pathobiology, 74(2), 63–71.
Kvasnicka, H. M., & Thiele, J. (2010). Prodromal myeloproliferative neoplasms: The 2008 WHO classification. American Journal of Hematology, 85(1), 62–69.
Tefferi, A., & Barbui, T. (2015). Polycythemia vera and essential thrombocythemia: 2015 update on diagnosis, risk-stratification and management. American Journal of Hematology, 90(2), 162–173.
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Kvasnicka, H.M. (2020). Essential Thrombocythemia (ET). In: Molina, T.J. (eds) Hematopathology. Encyclopedia of Pathology. Springer, Cham. https://doi.org/10.1007/978-3-319-95309-0_3811
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DOI: https://doi.org/10.1007/978-3-319-95309-0_3811
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