Essential thrombocythaemia (ET)
Essential thrombocythaemia (ET) is one of a group of conditions known as myeloproliferative disorders (MPDs).
To understand ET it helps to know a little about the bone marrow. Bone marrow is part of the immune system, which protects us from infection and disease. The marrow is in the spongy material found inside bones. This is where stem cells are made. Stem cells are blood cells at their earliest stage of development. All blood cells grow from stem cells. The three main types of blood cells are:
red blood cells – which carry oxygen around the body
white blood cells – which fight infections
platelets – which help blood to clot to prevent bleeding.
The bone marrow makes millions of blood cells every day. When the cells are mature they are released into the blood stream. In MPDs, the bone marrow makes too many of one or more types of blood cells.
These disorders affect how the bone marrow works. The main types of MPD are:
Some people with essential thrombocythaemia develop myelofibrosis. This is a condition in which the bone marrow becomes scarred. Rarely, people with MPDs develop leukaemia.
Essential thrombocythaemia (ET)
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ET is a rare condition affecting the bone marrow in which too many platelets are made. This means the number of platelets in the blood stream becomes higher than normal.
ET can affect people at any age, including children, but it's most common in people over 50. It usually develops very slowly and for most people doesn't affect their normal life span.
Signs and symptoms of ET
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Having too many platelets in the blood doesn’t always cause symptoms. Some people are diagnosed with ET after a blood test taken for other reasons. Possible symptoms of ET include:
redness, swelling or pain in the hands or feet due to reduced blood flow
Sometimes symptoms develop due to complications of ET, such as a blood clot caused by too many platelets in the blood. Less commonly, people may have bleeding or bruising because the platelets in their blood don't work properly.
Symptoms can occur because a blood clot (thrombosis) has formed in a vein in the body. Clotting problems are more common in people over 60, in people who have had a blood clot before, and in people who have conditions such as high blood pressure or diabetes.
Symptoms of a blood clot depend on where it is in the body. These are some common sites where a clot may form:
veins of the leg – causing pain, swelling, heat and redness, usually in the calf. This is known as deep vein thrombosis or DVT.
the brain – this may cause mild symptoms such as headaches, blurred vision, or dizziness. Blood clots in the brain may also cause a stroke or mini stroke (also called a transient ischaemic attack or a TIA). Symptoms may include weakness, numbness or pins and needles, or difficulties with speech or swallowing.
the heart – a blood clot in the heart may cause chest pain and, in severe cases, can result in a heart attack.
the lungs – a blood clot in a lung may cause breathlessness and chest pain. This is known as a pulmonary embolism or a PE.
Very occasionally ET can cause abnormal bleeding. This can cause symptoms such as:
abnormal vaginal bleeding
Diagnosis of essential thrombocythaemia
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ET is usually diagnosed by a specialist in blood disorders (haematologist). The diagnosis may be suspected after a routine blood test called a full blood count (FBC). This test counts the number of red blood cells, white blood cells and platelets. In ET there will be a high platelet count.
Other conditions can cause an increase in platelet count, such as an infection, arthritis, chronic bleeding or a lack of iron in the blood (anaemia). Your doctor will need to rule these out before a diagnosis of ET can be made.
Tests and investigations that may be done to confirm a diagnosis of ET are:
JAK2 blood test
This blood test checks for a change (mutation) in a gene called JAK2. This gene helps control how many blood cells are made. A change in the gene can cause ET. About half of all people with ET have a mutation in the JAK2 gene. This change in the gene happens during the person's lifetime. It isn't something you’re born with and you can’t pass it on to your children.
CALR blood test
People who do not have a mutation in JAK2 might be checked for a mutation in another gene called calreticulin (CALR). As with JAK2 mutations, change in the gene happens during the person's lifetime. It isn't something you’re born with and you can’t pass it on to your children.
Bone marrow sample (biopsy)
Your doctor may want to take a sample of marrow (biopsy) to be checked. The sample is usually taken from the back of your hip bone (pelvis). You’ll be given an injection of local anaesthetic to numb the area. The doctor will then pass a needle through the skin into the bone, and draw a small sample of liquid marrow (called a bone marrow aspirate) into a syringe.
After this, the doctor will take a small core of marrow from the bone (a trephine biopsy). Both samples will be looked at later under a microscope.
The test can be done on the ward or in the outpatients department. The whole procedure takes about 15 minutes. It may be uncomfortable when the marrow is drawn into the syringe, but this should only last for a few seconds.
You may feel bruised and sore for a few days after the test. You can take mild painkillers to help with this.
Treatment for essential thrombocythaemia
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Treatment for ET aims is to reduce the risk of complications, particularly blood clots. Your doctor will check your condition with regular blood tests.
If treatment is successful, the outlook for someone with ET is very similar to that of someone of the same age who doesn’t have the condition.
If you have a low risk of complications, you may be treated with aspirin. Aspirin can help prevent clots because it affects the way platelets 'stick together'. This doesn’t affect the platelet count, but can help lower the risk of blood clots. Side effects of aspirin include an increased risk of bleeding and ulcers in the stomach.
If you need to take a painkiller while you’re taking aspirin to prevent blood clots, ask your doctor for advice. Some types of painkillers, such as ibuprofen, may not be suitable.
Treatment to reduce platelet numbers (cytoreductive therapy)
If you are at high risk of complications, you will usually need treatment to reduce the numbers of platelets in your blood. This is called cytoreductive therapy.
This is the use of anti-cancer drugs to destroy cancer cells. Chemotherapy can also be used to treat non-cancer conditions. For ET it can be given to reduce the number of platelets.
Hydroxycarbamide is the most commonly used chemotherapy drug to treat ET. It is taken as a capsule or tablet. It can cause side effects, but generally these are mild. Side effects can include lowered resistance to infection , a reduced number of red blood cells (anaemia) , diarrhoea or constipation .
There is a very small risk of leukaemia developing if hydroxycarbamide is used for a long time. Patients under the age of 40 with ET may be given other drugs instead.
The chemotherapy drug busulfan (Busilvex ®, Myleran ®) may sometimes be used.
Busulfan is usually given as a tablet. It can cause similar side effects to hydroxycarbamide. There is also a risk of leukaemia developing if busulfan is used for a long time.
Chemotherapy may affect fertility. People taking it are advised not to get pregnant or father a child, as there may be a risk of harming the developing baby. It's advisable to use contraception while taking the drug and also for a few months afterwards.
Interferon alpha is a natural substance made by the body. It can also be made as a medicine (Busilvex ®, Myleran ®). It slows down the production of blood cells, including platelets. It is used most often to treat ET in younger people (under 40), although it can be used at any age. Interferon is given as an injection under the skin. Possible side effects include flu-like symptoms, headaches, dizziness, mood swings and tiredness.
Anagrelide is usually given when other treatments have already been tried. It's taken as a capsule. Side effects can include headaches and palpitations (a fast heartbeat). Some research studies suggest it may increase the risk of developing myelofibrosis.
It doesn't seem to affect fertility, but anagrelide should never be taken during pregnancy or if you are thinking of getting pregnant. It's important to use contraception when taking anagrelide.
Radioactive phosphorus (32P)
Radioactive phosphorus may be used to treat ET when other treatments have not worked or are unsuitable. It is given as an injection into a vein. It irradiates the bone marrow and can lower the number of platelets being made. The effects of a single injection can last from months to years.
Long-term treatment with radioactive phosphorus can cause an increased risk of leukaemia.
Your doctor or nurse will explain your treatment to you and answer any questions you have.
There are also some newer treatments available which may be used to help to control ET.
You may be invited to join a clinical trial looking at new ways of treating ET. You can talk about this with your haematology doctor.
Living with essential thrombocythaemia
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You will need to have regular check-ups and blood tests. If you have any problems, or notice any new symptoms in between appointments, let your nurse or doctor know as soon as possible.
Alongside the treatments and checkups recommended by your haematologist, you may want to look at ways of staying healthy. Following a healthy diet, drinking plenty of fluids, staying active and not smoking are good for your general health. This may also help reduce the risk of complications such as blood clots. Your doctor or specialist nurse can give you advice about this.
You may have many different emotions including anger and resentment, guilt, anxiety and fear. These are all normal reactions, and are part of the process many people go through in trying to come to terms with their condition.
Everyone has their own way of coping with difficult situations. Some people find it helpful to talk to family or friends, while others prefer to seek help from people outside their situation. Some people prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is there if you need it. Our cancer support specialists can give you information about counselling in your area.
MPD Voice is a support network for people with MPDs (myeloproliferative disorders) providing information and support.
Leukaemia CARE is a national group promoting the welfare of people with leukaemia and other blood disorders. It has regional support groups in many counties.
This information has been compiled using information from a number of reliable sources, including:
Harrison, Claire N, et al. Guideline for the investigation and management of adults and children presenting with a thrombocytosis. British Journal of Haematology. 2010. 149: 352–375.
Ansell, SM (Ed.). Rare Hematological Malignancies. 2008. Springer.
Thanks to Dr Tim Somervaille, Honorary Consultant Haematologist, who reviewed this edition.
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