What is Essential Thrombocythemia?

Last updated: April 2023

Essential thrombocythemia is one of several types of blood cancer called “myeloproliferative neoplasms,” or MPN. The common factor in these diseases is that immature cells in the bone marrow (called stem cells), which are supposed to mature into different kinds of blood cells, undergo mistakes in their genes that cause them to malfunction. Instead of multiplying and functioning normally, the irregular cells begin to grow without stopping, crowding out the normal blood cells that keep our bodies healthy. The different varieties of MPN depend on the types of cell that are affected.1

The stem cells in our bone marrow produce three main types of blood cells:

  • Red blood cells, which carry oxygen to nourish our cells
  • White blood cells, which fight infection
  • Platelets, which cause our blood to clot and stop bleeding1

Essential thrombocythemia is a rare type of MPN in which the bone marrow produces too many platelets. This can make the blood prone to clotting or developing a plug or “thrombus” that can interrupt blood flow. In rare instances, this can lead to a stroke, heart attack, or pulmonary embolism, which is the blockage of an artery in the lungs.2

How does essential thrombocythemia develop?

Essential thrombocythemia develops when a stem cell in the bone marrow undergoes a mistake, or mutation, in its genes.2 Genes exist in every cell and serve as an instruction manual for the cell’s functioning and reproduction. When the malfunctioning stem cell copies and divides itself, the mistake is passed onto the daughter cells, which themselves begin to divide and grow uncontrollably.

It is not clear what causes the initial mistake to develop in thrombocythemia. About 90 percent of people with this condition have an acquired gene mutation.3 In fact, a part of the diagnosis of thrombocythemia involves detecting mutations in one of three specific genes: JAK, CALR, or MPL.4

These gene mutations lead to the malfunctioning of a specific cell type called a megakaryocyte, which is one of our white blood cells. Megakaryocytes form platelets, so when they reproduce uncontrollably, the body ends up with too many platelets. Normally, you would expect to find about 150,000 to 450,000 platelets per microliter of blood. A person with thrombocythemia has more than 450,000.3

Additionally, despite the fact that there are excess platelets in thrombocythemia, they often do not function properly, so some people with this condition can experience abnormal clotting or even bleeding.3

What are the risk factors?

Essential thrombocythemia is a very rare disease. Its exact cause is not known, but researchers have noted certain factors that may increase your risk of developing the disease. These include:

  • Age: Essential thrombocythemia is more common among people over 60, although 20% of sufferers are under 40.
  • Gender: Women are 15% more likely to develop the condition than men.
  • Gene mutations: Nearly 50% of people with thrombocythemia have a mutation in a blood-forming gene called JAK2 and nearly 25% have a mutation in CALR.5

What are the symptoms?

Essential thrombocythemia often does not cause any noticeable symptoms. It is frequently diagnosed based on a routine blood test. Early symptoms may indicate the presence of a blood clot. A blood clot can be serious. The exact symptoms depend on where the clot forms. Common symptoms of a blood clot include:

  • Weakness
  • Fainting
  • Chest pain
  • Numbness or tingling in the hands and feet3,6

Additionally, about 50% of patients with essential thrombocythemia have an enlarged spleen. Many people experience this as a feeling of fullness near the stomach.

Sometimes one of the first symptoms of essential thrombocythemia is a blood clot that blocks blood flow in your brain. This is called a stroke. Signs and symptoms of a stroke include:

  • Headache
  • Dizziness
  • Weakness or numbness on one side of the body
  • Slurred speech
  • Double vision4

Some patients also experience bleeding as a symptom of thrombocythemia. This is rare, and symptoms include:

  • Easy bruising
  • Nosebleeds
  • Blood in the stool
  • Blood in the urine
  • Gastrointestinal bleeding4

Advanced cases may include additional symptoms:

What is a common prognosis?

Although there is no cure for essential thrombocythemia, most people with the disease have a normal life expectancy if they are treated and their disease is tracked by an experienced doctor.4,7

Treatment generally revolves around preventing clotting or excessive bleeding. If you are younger than 60 and do not have symptoms, you may simply need regular check-ups. Your doctor may prescribe medication if you are older than 60 and are at risk of blood clots or strokes or have heart problems.

Health care providers use a scoring system to determine how likely you are to experience clots. For people with low risk, sometimes the only medication they might need is a low-dose aspirin, which thins the blood.5,6

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