What Is Essential Thrombocythemia?

Essential thrombocythemia is a rare blood condition that affects platelets. Platelets are blood cells that control bleeding. Essential thrombocythemia is a type of myeloproliferative neoplasm (MPN). In these blood cancers, stem cells in the bone marrow do not work properly. Changes (mutations) in the cells’ genes cause them to grow without stopping.^1,2

Different types of MPN affect different blood cells. The stem cells in our bone marrow produce 3 main types of blood cells:^1,2

• Red blood cells: carry oxygen to nourish our cells
• White blood cells: fight infection
• Platelets: cause our blood to clot and stop bleeding

In essential thrombocythemia, the bone marrow produces too many platelets. This can make the blood prone to clotting. The blood can develop a plug (thrombus) that interrupts blood flow. People with essential thrombocythemia have a higher risk of:^1-3

• Heart attack
• Stroke
• Pulmonary embolism

What causes essential thrombocythemia?

Essential thrombocythemia is caused by a mutation in your genes. Genes serve as instructions for cells to function and reproduce.³

Essential thrombocythemia is caused by an acquired mutation in stem cells in your bone marrow. An acquired mutation happens when genes inside your cells mutate, or change. This type of genetic mutation is not inherited from your parents.^3-5

In essential thrombocythemia, the acquired mutation happens in 1 of 3 genes:^3-5

• Janus kinase 2 (JAK2) – Helps stem cells control the production of blood cells
• Calreticulin (CALR) – Controls how cells grow and divide
• Myeloproliferative leukemia virus – Promotes growth and division of cells

We do not yet know what causes these genes to acquire a mutation. But the mutation causes stem cells to reproduce uncontrollably. The mutation then passes into daughter cells. The stem cells produce too many platelets. These are blood cells that form clumps to plug holes in damaged blood vessels.^3,6

A normal level of platelets is 150,000 to 450,000 per microliter of blood. People with essential thrombocythemia can have more platelets than that. Their platelets may also be larger than normal or oddly shaped.^1,4

Abnormal platelets form blood clots that crowd blood vessels and block blood flow. People with essential thrombocythemia may also experience excessive bleeding because their platelets are used up by blood clots.^1,4

What are the risk factors for essential thrombocythemia?

Essential thrombocythemia is a very rare disease. It affects about 1 out of 50,000 people in the United States. Certain things may increase your risk. These include:^1,3,4

• Age – Essential thrombocythemia is most common among people between ages 60 and 80. About 1 in 5 people with the condition are under 40 years old.
• Sex – Women and people assigned female at birth are more likely to develop the condition.
• Gene mutations – Nearly half of people with essential thrombocythemia have a mutation in JAK2. Nearly a quarter have a mutation in CALR.

What are the symptoms of thrombocythemia?

You can have essential thrombocythemia and not notice any symptoms. You may learn you have it from a routine blood test that shows high platelet levels. Genetic testing and other blood tests can confirm a diagnosis.^3,5

Early symptoms may indicate a blood clot. A blood clot can form anywhere in the body. They typically form in your brain, hands, or feet. Common symptoms of a blood clot include:^3,4

• Seizures
• Shortness of breath
• Nausea
• Weakness or fatigue
• Fainting
• Chest pain
• Numbness or tingling in the hands and feet

About half of people with essential thrombocythemia have an enlarged spleen. Many people experience this as a feeling of fullness near the stomach.^1,5

Some symptoms may be caused by a blood clot that blocks blood flow in your brain. This is called a stroke. Symptoms of a stroke include:³

• Headache
• Dizziness
• Weakness or numbness on 1 side of the body
• Slurred speech
• Double vision

Some people experience bleeding. This is rare, but symptoms include:³

• Easy bruising
• Nosebleeds
• Blood in your urine or stool
• Gastrointestinal bleeding (bleeding in your digestive system)

What are the outcomes for people with essential thrombocythemia?

There is no cure for essential thrombocythemia. Treatments can reduce the risk of complications. Most people have a normal life expectancy with proper treatment and monitoring. Some people do not need treatment.³

Treatment is focused on reducing platelet levels and preventing clotting or bleeding. People under 60 without symptoms may simply need regular check-ups. Your doctor may prescribe medicine if you are older or have a risk of blood clots or stroke.¹

Your doctor will figure out your risk of blood clots by looking at your:^3,4

• Age
• Blood cell counts
• Other ongoing (chronic) conditions
• Genetic mutations

For people with low risk, doctors may suggest low-dose aspirin. Other possible treatments include:^3,4

• Droxia^® or Hydrea^® (hydroxyurea)
• Agrilyn^® (anagrelide)
• Multiferon^® (interferon alfa)
• Busulfex^® or Myleran^® (busulfan)
• Jakafi^® (ruxolitinib)