Essential thrombocythemia

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

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.

Abnormal blood clotting (thrombosis) is common in people with essential thrombocythemia and causes many signs and symptoms of this condition. 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. In addition, clots can travel to the lungs (pulmonary embolism), blocking blood flow in the lungs and causing chest pain and difficulty breathing (dyspnea).

Another problem in essential thrombocythemia is abnormal bleeding, which occurs more often in people with a very high number of platelets. Affected people may have nosebleeds, bleeding gums, or bleeding in the gastrointestinal tract. It is thought that bleeding occurs because a specific protein in the blood that helps with clotting is reduced, although why the protein is reduced is unclear.

Other signs and symptoms of essential thrombocythemia include an enlarged spleen (splenomegaly); weakness; headaches; or a sensation in the skin of burning, tingling, or prickling. Some people with essential thrombocythemia have episodes of severe pain, redness, and swelling (erythromelalgia), which commonly occur in the hands and feet.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

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. The CALR gene provides instructions for making a protein with multiple functions, including ensuring the proper folding of newly formed proteins and maintaining the correct levels of stored calcium in cells. The TET2 gene provides instructions for making a protein whose function is unknown.

The proteins produced from the JAK2, MPL, and THPO genes are part of a signaling pathway called the JAK/STAT pathway, which transmits chemical signals from outside the cell to the cell's nucleus. These proteins work together to turn on (activate) the JAK/STAT pathway, which promotes the proliferation of blood cells, particularly platelets and their precursor cells, megakaryocytes.

Mutations in the JAK2, MPL, and THPO genes that are associated with essential thrombocythemia lead to overactivation of the JAK/STAT pathway. The abnormal activation of JAK/STAT signaling leads to overproduction of megakaryocytes, which results in an increased number of platelets. Excess platelets can cause thrombosis, which leads to many signs and symptoms of essential thrombocythemia.

Although mutations in the CALR and TET2 genes have been found in people with essential thrombocythemia, it is unclear how these gene mutations are involved in development of the condition.

Some people with essential thrombocythemia do not have a mutation in any of the known genes associated with this condition. Researchers are working to identify other genes that may be involved in the condition.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

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 it is inherited, the condition is called familial essential thrombocythemia.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal platelet morphology · Very frequent (99-80%)

An anomaly in platelet form, ultrastructure, or intracellular organelles.

Abnormality of bone marrow cell morphology · Very frequent (99-80%)

An anomaly of the form or number of cells in the bone marrow.

Abnormality of the cerebral vasculature · Very frequent (99-80%)

An anomaly of the cerebral blood vessels.

Abnormality of thrombocytes · Very frequent (99-80%)

An abnormality of platelets.

Amaurosis fugax · Very frequent (99-80%)

A transient visual disturbance that is typically caused by a circulatory, ocular or neurological underlying condition.

Arterial thrombosis · Very frequent (99-80%)

The formation of a blood clot inside an artery.

Chest pain · Very frequent (99-80%)

An unpleasant sensation characterized by physical discomfort (such as pricking, throbbing, or aching) localized to the chest.

Fatigue · Very frequent (99-80%)

A subjective feeling of tiredness characterized by a lack of energy and motivation.

Other findings in the same source

From: Orphanet

Additional reported features include Increased megakaryocyte count (Very frequent (99-80%)); Megakaryocyte nucleus hyperlobulation (Very frequent (99-80%)); Myocardial infarction (Very frequent (99-80%)); Paresthesia (Very frequent (99-80%)); Prolonged bleeding time (Very frequent (99-80%)); Thrombocytosis (Very frequent (99-80%)); Venous thrombosis (Very frequent (99-80%)); Abnormal bleeding (Frequent (79-30%)); Headache (Frequent (79-30%)); Insomnia (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Essential thrombocythemia is Haematology, with a haematologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which blood-cell, marrow, bleeding or clotting finding matters most?
• Does the diagnosis need confirmation or a more precise subtype?
• Which symptoms or laboratory changes should trigger earlier review?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Essential thrombocythemia. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.