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Essential Thrombocythemia

National Organization for Rare Disorders, Inc.


It is possible that the main title of the report Essential Thrombocythemia is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • ET
  • essential hemorrhagic thrombocythemia
  • essential thrombocytosis
  • idiopathic thrombocythemia
  • idiopathic thrombocytosis
  • primary thrombocythemia

Disorder Subdivisions

  • None

General Discussion

Essential thrombocythemia (ET) is a rare, chronic disorder characterized by the overproduction of platelets. Platelets (also known as thrombocytes) are specialized blood cells that clump together to form clots to stop bleeding at the site of injury to blood vessels Although the overproduction of platelets is the or characteristic of ET, red blood cells and white blood cells may be overproduced to some degree as well.

Individuals with ET are at risk for the formation of blood clots (thrombosis), which can restrict blood flow to vital organs, and episodes of uncontrolled bleeding (hemorrhaging). Additional symptoms associated with ET include headaches, dizziness, bleeding from the gums or gastrointestinal tract, an enlarged spleen (splenomegaly) and a condition known as erythromelalgia, which is characterized by a reddened or purplish appearance to the skin of the hands and feet sometimes associated with a painful, burning sensation. Approximately two-thirds of individuals with ET do not have symptoms (asymptomatic) when initially diagnosed. In fact, a diagnosis of ET is often made incidentally during a routine examination. Many individuals eventually present with symptoms related to small or large vessel thrombosis or minor bleeding. Presentation with a major bleeding episode is very unusual. The exact, underlying cause of ET is unknown. However, more than half of the people with this disorder have a mutation of the JAK2 gene. The exact role that this gene plays in the development of ET is not fully understood.

Essential thrombocythemia belongs to a group of diseases known as the myeloproliferative disorders (MPDs). This group of disorders is characterized by the overproduction (proliferation) of one or more of the three main blood cell lines - red or white blood cells or platelets. Red blood cells carry oxygen to the body. White blood cells fight infection. Platelets are involved in clotting of the blood in response to injury. Three other disorders are commonly classified as MPDs: chronic myelogenous leukemia, polycythemia vera and idiopathic myelofibrosis. Because the MPDs are characterized by uncontrolled cell growth, they may also be classified as blood cancers.


Leukemia & Lymphoma Society

1311 Mamaroneck Avenue

Suite 310

White Plains, NY 10605

Tel: (914)949-5213

Fax: (914)949-6691

Tel: (800)955-4572



American Cancer Society, Inc.

250 Williams NW St

Ste 6000

Atlanta, GA 30303


Tel: (404)320-3333

Tel: (800)227-2345

TDD: (866)228-4327


NIH/National Heart, Lung and Blood Institute

P.O. Box 30105

Bethesda, MD 20892-0105

Tel: (301)592-8573

Fax: (301)251-1223



NIH/National Heart, Lung and Blood Institute ~ Hematology Branch

10 Center Dr, Building 10-CRC

3-5140, MSC-1202

Bethesda, MD 20892-1202

Tel: (301)496-5093

Fax: (301)496-8396

Tel: (800)644-2337



Platelet Disorder Support Association

133 Rollins Avenue, Suite 5

Rockville, MD 20852


Tel: (301)770-6636

Fax: (301)770-6638

Tel: (877)528-3538



Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223


CMPD Education Foundation

P.O. Box 4758

Scottsdale, AZ 85261



Madisons Foundation

PO Box 241956

Los Angeles, CA 90024

Tel: (310)264-0826

Fax: (310)264-4766



Myeloproliferative Disease Support and Daily Email Digest

2011 Flagler Ave.

Key West, FL 33040


Tel: (305)295-4444



MPN Research Foundation

180 N. Michigan Avenue, Suite 1870

Chicago, IL 60601

Tel: (312)683-7249

Fax: (312)332-0840



For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders (NORD). A copy of the complete report can be downloaded free from the NORD website for registered users. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational therapies (if available), and references from medical literature. For a full-text version of this topic, go to and click on Rare Disease Database under "Rare Disease Information".

The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only. NORD recommends that affected individuals seek the advice or counsel of their own personal physicians.

It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report

This disease entry is based upon medical information available through the date at the end of the topic. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.

For additional information and assistance about rare disorders, please contact the National Organization for Rare Disorders at P.O. Box 1968, Danbury, CT 06813-1968; phone (203) 744-0100; web site or email

Last Updated:  1/3/2012

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