Essential thrombocythemia (ET) is a condition in which the bone marrow produces too many platelets. Platelets are a part of the blood that aids in blood clotting.
ET results from an overproduction of platelets. Untreated, ET worsens over time. Because these platelets do not work normally, blood clots and bleeding are common problems.
ET is part of a group of conditions known as myeloproliferative disorders. Others include:
- Chronic myelogenous leukemia (cancer that starts in the bone marrow)
- Polycythemia vera (bone marrow disease that leads to an abnormal increase in the number of blood cells)
- Primary myelofibrosis (disorder of the bone marrow in which the marrow is replaced by fibrous scar tissue)
Many people with ET have a mutation of a gene (JAK2, CALR, or MPL).
ET is most common in middle aged people. It can also be seen in younger people, especially women under age 40.
Symptoms of blood clots may include any of the following:
- Headache (most common)
- Tingling, coldness, or blueness in the hands and feet
- Feeling dizzy or lightheaded
- Vision problems
- Mini-strokes (transient ischemic attacks) or stroke
If bleeding is a problem, symptoms may include any of the following:
Exams and Tests
Most of the time, ET is found through blood tests done for other health problems before symptoms appear.
Your health care provider may notice an enlarged liver or spleen on physical examination. You may also have abnormal blood flow in the toes or feet that causes skin damage in these areas.
Other tests may include:
If you have life-threatening complications, you may have a treatment called platelet pheresis. It quickly reduces platelets in the blood.
Long-term, medicines are used to decrease the platelet count to avoid complications. The most common medicines used include hydroxyurea, interferon-alpha, or anagrelide. In some people with a JAK2 mutation, specific inhibitors of the JAK2 protein may be used.
In people who are at a high risk of clotting, aspirin at a low dose (81 to 100 mg per day) may decrease clotting episodes.
Many people do not need any treatment, but they must be followed closely by their provider.
While outcomes can vary, most people can go for long periods without complications and have a normal lifespan. In a small number of people, complications from bleeding and blood clots can cause serious problems.
In rare cases, the disease can change into acute leukemia or myelofibrosis.
Primary thrombocythemia; Essential thrombocytosis
Hoffman R, Kremyanskaya M, Najfeld V, et al. Essential thrombocythemia. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, Anastasi J, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 68.
Tefferi A. Polycythemia vera, essential thrombocythemia, and primary myelofibrosis. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 166.
Review Date 2/1/2017
Updated by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.