Essential thrombocythaemia (ET): symptoms, diagnosis and treatment

Essential thrombocythaemia (ET) is, in Blood Cancer UK's words, a type of blood cancer that causes your body to make too many blood cells called platelets. Platelets help your blood clot, sticking together to stop you bleeding if you have a cut or bruise. They are made in the bone marrow by large cells called megakaryocytes. In ET, the megakaryocytes make too many platelets, so the blood may clot too easily.

Leukaemia Care describes ET as a slow-growing blood cancer in a group of conditions called myeloproliferative neoplasms (MPNs). The name is partly out of date: Blood Cancer UK explains that "essential" means the cause is not known, but we now know ET starts with genetic changes that happen during a person's lifetime. Most people, including medical staff, simply say "ET".

Blood Cancer UK says many people will not have noticed any symptoms when they are diagnosed, and that ET is picked up when they have a blood test for something else. You are more likely to have symptoms if you are older or have a very high platelet count.

• Headaches and dizziness.

• Visual changes, often called light shows or silent migraines.

• Difficulty concentrating and tiredness (fatigue).

• Bruising or bleeding, such as nose bleeds, blood in your poo or heavy periods.

• Pain in the tummy (abdomen).

• Burning pain, most commonly in the feet, but possibly in the hands, arms, legs, ears or face; lighter skin tones may look red in these areas.

• Itchy skin in some people.

Blood Cancer UK says ET can cause thrombosis, or blood clots, which is a serious condition. In the brain, clots can cause stroke or mini stroke (TIA); in the eyes, blurred vision or loss of sight; in the heart, a heart attack; in the tummy area, damage to organs such as the liver; and in the legs, deep vein thrombosis (DVT), which can break free and travel to the lungs (pulmonary embolism).

It says symptoms that need an immediate 999 call include slurred speech, weakness on one side of the body, drooping on one side of the face, sudden chest pain, dizziness and shortness of breath, one leg or arm becoming painful, swollen and warm, coughing up blood, sudden blurred vision or loss of sight, and sudden tummy pain, possibly with swelling and jaundice.

It also explains that, although it may seem odd, bleeding can happen when the number of platelets is very high and they do not work normally, so your hospital team will monitor you for unusual bleeding as well as thrombosis.

Blood Cancer UK says ET is caused by specific genetic changes that happen during someone's lifetime, though it is not known why this happens. It is more common in people over 50 years old, although younger adults can get it, and is slightly more common in women than in men. Most people with ET have a mutation in one of three genes, JAK2 (50 to 60 in every 100 people with ET), CALR or MPL.

Blood Cancer UK says a platelet count that stays high over an extended period shows up in blood tests, but other conditions can also raise platelets, including other cancers, infections, iron deficiency and inflammatory conditions such as rheumatoid arthritis, so you will need tests to check ET is the right diagnosis.

Tests described by Blood Cancer UK include a full blood count, other blood tests to check kidney and liver function, genetic tests looking for changes in JAK2, CALR or MPL, an ultrasound scan of the abdomen to look at the spleen (which may be swollen), and sometimes a bone marrow biopsy. Leukaemia Care says your haematology team uses blood tests and bone marrow tests to diagnose ET.

Leukaemia Care says not everyone with ET needs treatment straight away; some people have regular check-ups (active monitoring). Most treatments aim to control ET rather than cure it, and some are to prevent or manage complications.

Leukaemia Care says people with ET usually live long lives, though outcomes vary from person to person, and that it can only give general figures and cannot say what will happen for any one person.

It explains that occasionally ET changes (transforms) into a different type of blood cancer: polycythaemia vera (too many red blood cells), myelofibrosis (the bone marrow becomes inflamed and scarred) or acute myeloid leukaemia (a faster-growing blood cancer). Your haematology team will monitor you for this, and if ET transforms your symptoms and blood counts may change.

Blood Cancer UK and Leukaemia Care both stress that, once diagnosed, you can start taking medicine that brings down the risk of thrombosis, and that knowing the warning signs of a clot is important. Blood Cancer UK says to talk to your GP or hospital team if you have one or more symptoms that you cannot explain.

A diagnosis described as blood cancer can feel frightening even when there are few symptoms; Blood Cancer UK includes a quote from a person with ET who said it was more psychological than physical, and points to information on looking after your mental health. Blood Cancer UK also offers access to specialist blood cancer nurses for questions and worries.

On the NHS, a raised platelet count found by a GP is usually followed by repeat testing and referral to a haematology team for genetic tests and, where needed, a bone marrow biopsy. Treatment and monitoring are led by haematology. Some people seek a private haematology opinion, but because ET is rare and long term, most ongoing care stays with an NHS specialist team, with the GP involved in managing clot risk factors.