title: Essential thrombocythemia: a review of diagnostic and pathologic features.
abstract: BACKGROUND
  Essential thrombocythemia (ET) is a chronic myeloproliferative disorder (CMPD) characterized predominately by thrombocytosis and abnormal megakaryocyte proliferation. The current diagnostic criteria require a combination of clinical, histologic, and cytogenetic data. The diagnosis relies largely on exclusion of other causes of thrombocytosis.
  
  
  OBJECTIVE
  Describe historical, clinical, and laboratory features of ET in order to understand, clarify, and more accurately diagnose this entity.
  
  
  METHODS
  Review contemporary and historical literature on ET and other causes of thrombocytosis.
  
  
  CONCLUSIONS
  ET is a relatively indolent and often asymptomatic CMPD that is characterized primarily by a sustained elevation in platelets > or = 600 x 10(3)/microL (> or = 600 x 10(9)/L), proliferating enlarged and hyperlobated megakaryocytes, and minimal to absent bone marrow fibrosis. Significant changes and revisions to the diagnostic requirements and criteria for ET have occurred during the last 30 years. Recently, a mutation in the Janus kinase 2 (JAK2) gene has been found in a significant number of cases of ET and other CMPDs. In up to 57% of ET cases, a mutation in the JAK2 gene can be detected. In the absence of a JAK2 mutation and features of another CMPD, the diagnosis of ET remains a diagnosis of exclusion after other causes of thrombocytosis have been excluded.
authors.affiliation: Department of Pathology, The Methodist Hospital, Houston, Tex 77030, USA. stevensanchez@tmh.tmc.edu
authors.forename: Steven
authors.initials: S
authors.lastname: Sanchez
authors.forename: April
authors.initials: A
authors.lastname: Ewton
mesh_terms: D001792:Blood Platelets / Q000473:pathology; D049109:Cell Proliferation; D006801:Humans; D053614:Janus Kinase 2; D008533:Megakaryocytes / Q000473:pathology; D010976:Platelet Count; D017354:Point Mutation; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics; D013920:Thrombocythemia, Essential / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology*; D013922:Thrombocytosis / Q000473:pathology
chemical_list: D011518:Proto-Oncogene Proteins; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2