Idiopathic thrombocytopenic purpura

Idiopathic thrombocytopenic purpura (ITP) is a rare autoimmune disorder, in which the blood doesn’t clot properly because the platelets that help blood to clot are destroyed by antibodies.

Blood is partly made up of platelets (thrombocytes), which are small cell-like bodies that are important in blood clotting. Normally, platelet counts number between 150,000 and 450,000, but a person with ITP may have a platelet count of 20,000 or lower.

Causes and risk factors
The cause of ITP is unknown, but it is thought that viral infections cause the immune system to malfunction and start producing ‘rogue’ antibodies.

There are two broad categories of ITP: one that usually resolves by itself with time and the other that lingers beyond six months. ITP is more common among children than adults, most often occurring around two to four years of age. Estimates suggest that one in every 10,000 children is affected. Among adults, young women are more likely to develop ITP than any other group, for reasons unknown.

Symptoms
In general, the person appears and feels perfectly well. There may be no symptoms of ITP until the platelet count is extremely low. Symptoms may include:

• The skin bruises very easily
• A skin rash of small red dots (petechiae)
• The skin rash does not blanche with pressure
• Bleeding from any area of the body
• Bleeding from the gums
• Frequent nosebleeds that take a long time to stop
• Internal bleeding
• Abnormal menstruation.

Two categories of ITP
The two categories of ITP include:

• Acute – this is primarily a disease of childhood where it accounts for nine out of 10 cases of ITP. It is far less common in adults, who are more likely to have chronic ITP. Sometimes, the condition seems to be triggered by a viral infection (such as a cold). The disease resolves by itself within two to six months.
• Chronic – this ongoing form accounts for most ITP seen in adults and is far less common in children. Chronic ITP has similar symptoms to acute ITP, except that it lingers for longer than six months.

Malfunction of the immune system
The immune system is a specialised system of cells and chemicals that fight infections. Normally, the immune system recognises ‘self’ and doesn’t attack tissues or organs of the body.

It is thought that ITP is triggered by some types of viral infections. For reasons unknown, these infections prompt the lymph tissues and spleen to make antibodies that attack the platelets in the blood. Antibodies that attack the body are called autoantibodies. In other cases, the case is unknown (idiopathic).

Platelets are made in the bone marrow. Since ITP targets mature platelets as they circulate through the spleen, the ‘newborn’ platelets inside bone marrow are healthy and normal. In many cases of acute ITP, the platelet count will rise again within a few weeks and return to normal within a few months.

Diagnosis
Very often ITP has no symptoms and may be discovered during blood tests for an unrelated medical matter. ITP is diagnosed by taking a medical history and physical examination, coupled with some laboratory investigations including:

• Blood tests – such as a full blood examination (FBE) to check for platelet numbers and a test to check for the presence of platelet antibodies.
• Other tests – to exclude other conditions that may cause a low platelet count, such as acute leukaemia and aplastic anaemia.
• Bone marrow biopsy – a small sample of bone marrow is taken via needle and then checked in a laboratory. In ITP, the platelets produced in the bone marrow should be normal. This test is only used when strictly necessary, since it is invasive and carries some risk.

Treatment
Treatment for ITP may include:

• Time and close observation – in some cases, ITP resolves by itself. In severe cases, the symptoms of the disorder (such as the tendency to spontaneously bleed) must be managed in the meantime.
• Corticosteroids – drugs to reduce the activity of the immune system. Corticosteroids may be administered as intravenous injections or tablets.
• Intravenous immunoglobulin (IVG) – the antibodies are ‘caught’ by the IVG and culled from the bloodstream.
• Plasmapheresis – the blood is filtered through a special machine that removes the antibodies in blood plasma. This treatment is generally used in severe cases only.
• Splenectomy – surgical removal of the spleen. This procedure cures ITP in about 70 to 80 per cent of chronic cases.
• Monoclonal antibodies to CD20 – an injection treatment targeting antibody producing cells.
• Thrombopoietin analogues – treatment to increase the production of new platelets in the bone marrow.
• Ongoing monitoring – the platelet count is regularly monitored. Treatment is often recommenced every time the platelet count drops below a critical figure (usually when it is less than 20,000) or prior to surgical procedures to reduce the bleeding risk. Relapses may occur. Occasionally, the person who appears to have been cured of ITP will experience a relapse, perhaps months or even years after the initial episode. Repeat treatment is needed. In most cases, the relapse seems to be triggered by a viral infection.

Where to get help

• Your doctor

Things to remember

• Idiopathic thrombocytopenic purpura (ITP) is a rare autoimmune disorder, in which the blood doesn’t clot properly because the blood clotting platelets are destroyed by antibodies.
• The cause of ITP is unknown, but it is thought that some kinds of viral infection cause the immune system to malfunction and start producing antibodies that attack platelets.
• Treatment options include ongoing monitoring of platelet levels, medications and surgical removal of the spleen in severe cases.

You might also be interested in:

• Immune system.
  

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Australian Centre for Blood Diseases

Fact sheet currently being reviewed.
Last updated: April 2009

The information published here was accurate at the time of publication and is not intended to take the place of medical advice. Please seek advice from a qualified healthcare professional.

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