What is Essential Thrombocythaemia (ET)?

Essential thrombocythaemia (ET), in common with other Myeloproliferative neoplasms (MPNs), is a disease resulting from an increase in cell number due to cell growth and division of stem cells, resulting in increased platelet production.1

The normal range for platelet count is 150 – 400 x 109/L or 150 – 400 billion platelets per litre of your blood.2 Platelets are non-nucleated fragments from megakaryocytes, which circulate in your blood, and help the blood to clot. When there are too many platelets in your blood, the risk of suffering from blood clots or from excess bleeding increases.3 It is possible to use medication to bring down high platelet levels and this may reduce the risk of such ET complications.2

The effects of lowering platelet count may have the greatest benefit when platelet counts are reduced close to or within the normal range (150 – 400 x 109/L). ET patients have a near-normal life expectancy, and should be assessed and managed based on their individual risks and the benefit-risk profile of treatments.2

Blood cells do not live forever. The body continuously makes blood cells and old ones are constantly being removed. However, in ET, too many platelets are made and this leads to a build-up of platelets in the blood.3

The exact mechanism by which platelets are activated in ET is yet to be defined, but people with ET have an increased number of the cells that produce platelets. These cells are called megakaryocytes. Megakaryocytes are made in the bone marrow and form elongated structures, from which individual platelets form.3 There may be a genetic cause in some patients, but this is still being researched. 1

Fewer than 3 people per 100,000 are diagnosed with ET each year. The age of onset of ET covers a wide range. ET tends to be diagnosed during the third of fourth decade of life, but the median age of diagnosis is 65 to 70 years. The incidence of ET is two times higher in women.1

It is common not to have any symptoms from ET; at diagnosis, approximately 50% of people have no symptoms. Medication may be prescribed where the risk of the disease outweigh possible side effects.2

High platelet counts can cause problems by making blood clot in the blood vessels. This can prevent blood reaching important parts of the body, and cause serious conditions such as strokes and heart attacks, which can be associated with a reduction in quality of life. However, effective treatment of ET can reduce the risk of these complications.3

ET patients can also experience bleeding complications. Bleeding symptoms are more often observed in patients with high platelet counts. This means that a patient may experience an increased amount of bleeding, such as increased gum bleeding, nose bleeds, or bleeds within the digestive system.1

Clotting can cause other symptoms of ET and these include headaches, blood clots in the legs and pain in the hands or feet. If you think that you are developing these or any other symptoms, it is very important that you tell your doctor.1

References:
1. Brière JB. Essential thrombocythemia. Orphanet J Rare Dis. 2007;2(3):1-17.
2. Barbui T, Barosi G, Birgegård G, Cervantes F, Finazzi G, Griesshammer M, et al. Philadelphia-Negative Classical Myeloproliferative Neoplasms: Critical Concepts and Management Recommendations from European LeukemiaNet. 2011;29:761-770.
3. Andrews RK, Berndt MC, Elalamy I. Platelets – from function to dysfunction in essential thrombocythaemia. Eur Oncol Haematol. 2011:125-131.
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