Introduction

This leaflet explains about idiopathic thrombocytopenic purpura, which is a blood disorder affecting the platelets. It also explains what to expect when your child is diagnosed with the condition.

What are platelets?

Platelets are one of the three types of blood cell, along with red and white blood cells. Platelets are small and sticky and their job is to prevent bruising and stop bleeding after an injury.

Platelets, like red and white blood cells, are formed in the bone marrow, which is found in the middle of most bones in the body. The bone marrow cells which release platelets into the bloodstream can be examined closely by taking a small sample of bone marrow and looking at it under a microscope. A rough idea of how many platelets are circulating in the bloodstream (platelet count) can be made using a sample of blood, but usually a more detailed examination of bone marrow is needed. The normal platelet count is between 150,000 and 400,000 platelets per cubic millimeter. This is usually expressed as 150 to 400 x 109/l.

A low platelet count is usually around 40 x 109/l, and is called ‘thrombocytopenia’.

What can cause a low platelet count?

There are various reasons why your child’s platelet count may be lower than usual and these are described below. The various tests your child has will confirm or rule out each of these possibilities so that the doctor can give you a firm diagnosis.

·         The bone marrow may not be working properly and so not forming platelets. This can happen with bone marrow failure or leukemia, but a child with these conditions usually shows other symptoms, like anemia (low red blood cell count) or bone pain.

·         The spleen (an organ near the stomach that helps to control the blood’s composition) may not be working properly. The spleen stores a large number of platelets in reserve, so if it is very large, it may not be releasing enough platelets into the bloodstream. However, spleen problems rarely cause bleeding.

·         The bone marrow may be producing enough platelets but they may not be lasting as long as normal in the bloodstream. There are a number of reasons why this may happen:

·         There may be an inherited problem which means that the platelets are not working properly. So, although your child may have enough platelets in the bloodstream, he or she will have symptoms of a low platelet count, like bruising and bleeding. Other members of the family may be affected too, and show similar symptoms.

·         Sometimes, the body does not produce enough platelets after heavy blood loss or clotting after an operation, tooth extraction or serious infection, probably because the bone marrow isn’t working well enough to keep up the supply

The bone marrow may be producing platelets at the normal rate, but they are destroyed quickly because the body has formed antibodies to them. This means that the body sees the platelets as ‘the enemy’ and so the liver, spleen and bone marrow destroy them. This is know as idiopathic thrombocytopenic purpura (or ITP for short) – see more information in the later section, called “What is idiopathic thrombocytopenic purpura?”

What are the effects of a low platelet count?

There are no major problems if your child’s platelet count is just under 150 x 109/l unless major surgery is planned, in which case their blood clotting efficiency would be further investigated. If your child’s platelet count is 40 x 109/l or below, they may develop bruising and red pinprick spots on the skin (petechiae) particularly on their neck and waist. However, these are not usually serious and do not require treatment. If your child’s platelet count is lower than 20 x 109/l, he or she could develop more serious bruising, and may be at risk of bleeding, including internal bleeding.

The risk of bruising and bleeding also depends on what is causing the low platelet count. In some rare conditions, not only are there too few platelets circulating in the blood, but those that exist do not work properly. This leads to a higher risk of more severe bleeding, regardless of the platelet count itself.

What is idiopathic thrombocytopenic purpura?

Idiopathic thrombocytopenic purpura is a medical term for a condition in which there is bruising (purpura) because there are fewer platelets in the blood than usual (thrombocytopenic) and we are not sure what causes it (idiopathic). You may hear the condition referred to as ‘immune’ thrombocytopenic purpura, which just means that it could have been caused by something going wrong with the immune system (the body’s defence against infection) or an allergic reaction of some kind.

What are the symptoms of ITP?

The main symptom is that your child may develop serious bruising on any part of their body or may bleed from their nose and gums. However, a child with ITP will bleed less than a child with a low platelet count caused by other conditions. We think that this is because the platelets are being made and destroyed so fast that only young, active platelets (which are good at clotting) are circulating in the blood. This means that although children with ITP may bruise a great deal, their risk of serious bleeding is low. A UK-wide survey has put this risk at less than one in every 500 children, and in some of these cases the bleeding was caused by an injury. Serious internal bleeding only occurs in children with a very low platelet count, and although ITP is a frightening illness, the risk of this happening to your child is extremely low.

Sometimes, ITP develops gradually and it is important to check that your child’s low platelet count is not caused by one of the lifelong platelet abnormalities. For example, the body very occasionally produces antibodies against other parts of the body, such as red blood cells or smooth muscles. This may be harmful and it is important to know if it is happening.

What causes ITP?

We are not sure what causes ITP, but it can follow childhood viral infections, like chickenpox. We think that this may trigger the body to produce antibodies to destroy the virus but which stick to the platelets as well, so that the spleen and liver see them as unfamiliar, and destroy them.

How is ITP diagnosed?

It is usually diagnosed using a blood test called a ‘full blood count’. When a sample of your child’s blood is examined under a microscope, the technician can examine each blood cell type closely. This is to rule out other conditions that may cause similar symptoms to ITP. If the platelets, red blood cells and white blood cells look normal, this rules out bone marrow failure or leukemia. If the low platelet count improves quickly and no treatment is needed, your child will not need any further tests.

However, if this is not the case, then a small sample of bone marrow will need to be taken and examined under the microscope. For more information about this, please see our leaflet Your child is having a bone marrow test: information for families. If the bone marrow looks normal with the usual or higher number of platelet parent cells (megakaryocytes), then the doctor will diagnose ITP.

Children with a long history of bruising may need further tests on a larger sample of bone marrow (trephine). This shows how well the bone marrow is working and rules out bone marrow failure. Other tests to show how well the platelets are working may also be needed to rule out one of the lifelong platelet disorders.

How common is ITP and who does it affect?

About four in every 100,000 children develop ITP each year. There seem to be two groups who develop ITP: young children and young adults. It is more common in girls than boys.

How is ITP treated?

Most children do not need any treatment unless they have severe bruising or bleeding, and most children improve whether or not treatment is given. The type of treatment recommended depends on your child’s symptoms rather than their platelet count, and all the various forms of treatment aim to relieve symptoms rather than cure the condition itself. When treatments are considered, you will have the chance to discuss the risks and benefits of these, as opposed to no treatment, with the doctor. The options for treating severe ITP include:

·         Steroid treatment
Steroids are sometimes given to children with ITP on a short-term basis in an attempt to increase their platelet count. However, when the steroid dose is reduced, the platelet count often drops again. This can sometimes lead to the dose being increased and decreased over a long period according to the platelet count. Steroids should only be given for a short period of three to four weeks, as after this time, the side effects of the steroids outweigh the risk of serious bleeding. You can read more about steroids in our leaflet Short term steroid treatment: information for families.

·         Intravenous immunoglobulin
Immunoglobulins are antibodies which can reduce platelet destruction. However, the effects do not last very long. After one course of treatment with immunoglobulin, which takes five days, the platelet count can improve dramatically, but usually returns to previous levels within one to two weeks. Repeated injections are quite unpleasant and do not cure ITP. They are best used to deal with specific symptoms such as serious nosebleeds.

·         Removal of the spleen (splenectomy)
As the spleen (an organ near the stomach which helps to control the composition of the blood) is one of the places where platelets are destroyed, surgery to remove it can be helpful. However, the long term effect of removing the spleen is that your child may have an increased risk of catching certain infections. For more information about the splenectomy operation and this long term effect, please see our leaflet, Splenectomy: information for families.

·         Other treatments
There are other treatments available including drugs which damp down the immune system, but these are still undergoing trials to see if they produce good effects. These treatments should only be used for children with serious long term problems or complex immune system disorders.

What is the outlook for children with ITP?

Just as we do not understand what causes ITP, we do not understand why many children suddenly recover from it. Most children, particularly younger ones, suddenly improve within a few weeks or months, whether or not treatment has been given. Nine out of ten children will have improved within a year of diagnosis. However, one in ten children will have a low platelet count for some years before it improves. This will not restrict their life in any way, but it may be sensible to avoid sports where the risk of bruising or cutting themselves and bleeding is high. Your child should also avoid drugs like aspirin which can increase the risk of bruising and bleeding. Finally, you should make sure that doctors know that your child has a low platelet count if they are due to have an operation.

ITP in children produces frightening symptoms but it has a good outlook, with most children having no lasting effects from the condition. Once a firm diagnosis of ITP is made, your child will not need repeated blood tests and for the majority of children no treatment is needed.