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Essential thrombocythemia
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Essential thrombocythemia

Essential thrombocythemia is a rare blood disorder characterized by an overproduction of platelets, which significantly increases the risk of abnormal blood clotting and bleeding complications.

Overview

Essential thrombocythemia is a condition characterized by an increased number of platelets (thrombocythemia). Platelets (thrombocytes) are blood cells involved in blood clotting. While some people with this condition have no symptoms, others develop problems associated with the excess platelets.

Symptoms

The signs and symptoms of essential thrombocythemia are primarily related to abnormal blood clotting and bleeding issues. They include:

  • Abnormal blood clotting (thrombosis): Clots that block blood flow to the brain can cause strokes or temporary stroke-like episodes known as transient ischemic attacks. Thrombosis in the legs can cause leg pain, swelling, or both.
  • Pulmonary complications: Clots can travel to the lungs, blocking blood flow and causing chest pain and difficulty breathing (dyspnea).
  • Abnormal bleeding: Occurring more often in people with a very high number of platelets, this can cause nosebleeds, bleeding gums, or bleeding in the gastrointestinal tract. This is thought to occur because a specific protein in the blood that helps with clotting is reduced.
  • Enlarged spleen (splenomegaly)
  • Systemic symptoms: Weakness, headaches, or a burning, tingling, or prickling sensation in the skin.
  • Erythromelalgia: Episodes of severe pain, redness, and swelling, which commonly occur in the hands and feet.

Frequency

Essential thrombocythemia affects an estimated 1 to 24 per 1 million people worldwide.

Causes

The JAK2 and CALR genes are the most commonly mutated genes in essential thrombocythemia. The MPL, THPO, and TET2 genes can also be altered in this condition.

The JAK2, MPL, and THPO genes provide instructions for making proteins that promote the growth and division (proliferation) of blood cells. These proteins are part of a signaling pathway called the JAK/STAT pathway, which transmits chemical signals from outside the cell to the cell's nucleus. They work together to activate the pathway, promoting the proliferation of blood cells, particularly platelets and their precursor cells, megakaryocytes.

Mutations in the JAK2, MPL, and THPO genes associated with essential thrombocythemia lead to overactivation of the JAK/STAT pathway. This abnormal activation leads to the overproduction of megakaryocytes, resulting in an increased number of platelets. Excess platelets can cause thrombosis, leading to the primary symptoms of the condition.

The CALR gene provides instructions for making a protein with multiple functions, including ensuring the proper folding of newly formed proteins and maintaining correct calcium levels in cells. The TET2 gene provides instructions for making a protein whose function is unknown. Although mutations in these genes are found in affected individuals, it remains unclear how they contribute to the development of the condition.

Some people with essential thrombocythemia do not have a mutation in any of the known associated genes.

Associated Genes

  • CALR
  • JAK2
  • MPL
  • TET2
  • THPO

Inheritance

Most cases of essential thrombocythemia are not inherited. Instead, the condition arises from gene mutations that occur in early blood-forming cells after conception. These alterations are called somatic mutations.

Less commonly, essential thrombocythemia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. When inherited, the condition is referred to as familial essential thrombocythemia.

Other Names for This Condition

  • Essential thrombocytosis
  • Primary thrombocythemia
  • Primary thrombocytosis

Frequently Asked Questions

You should seek immediate medical attention for sudden severe chest pain or difficulty breathing, sudden weakness or numbness on one side of the body, slurred speech, severe headache, or sudden leg pain and swelling, as these could indicate a serious blood clot. Unexplained significant bleeding, like heavy nosebleeds or blood in stool, also warrants urgent evaluation.
Treatment often involves medications to lower platelet counts, such as hydroxyurea or anagrelide, and antiplatelet drugs like aspirin to reduce the risk of blood clots. The specific approach depends on your age, symptoms, and overall risk factors.
While lifestyle changes don't cure the condition, maintaining a healthy lifestyle is important. This includes staying hydrated, avoiding smoking, managing other cardiovascular risk factors like high blood pressure and cholesterol, and regular, moderate exercise as advised by your doctor. Discuss any dietary concerns with your healthcare provider.
Most cases of essential thrombocythemia are acquired, meaning the gene mutations (like JAK2, CALR, or MPL) occur spontaneously during a person's lifetime and are not inherited from parents. Familial cases are rare, but genetic counseling can be helpful if there's a family history.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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