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idiopathic thrombocytopenic purpura Alternative Names
autoimmune thrombocytopenia, ITP
Definition
Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease that causes very low platelet counts.
What is going on in the body?
Platelets, which are made by the bone marrow, are essential for blood clotting. In ITP, the body produces antibodies that attack the platelets and destroy them. Normally the body makes antibodies to fight infections. In ITP, the body for some reason makes antibodies that attack platelets, called autoantibodies, and these act to destroy platelets. The result is a low platelet count, known as thrombocytopenia. The cause of this disorder is unknown. But certain viral infections seem to cause this autoimmune response, where the body begins to attack itself. This in turn creates antibodies that attack the platelets, which are then removed from the bloodstream. Normal platelet counts are between 150,000 and 450,000. People with ITP may have very low platelet counts, often lower than 20,000 to 50,000.
What are the signs and symptoms of the disease?
Usually there are no signs or symptoms of ITP until the platelet count becomes quite low. The viral infection that precedes ITP may be an ordinary one, even a simple upper respiratory infection. If the platelet count falls to an extremely low level or 5,000 to 10,000, spontaneous bleeding may occur. This bleeding may occur at any site in the body. Usually it starts as easy bruising and bleeding from the gums. A more severe form is internal bleeding, which can occur in the brain or the vital organs in the stomach area.
What are the causes and risks of the disease?
There are no known risk factors for developing ITP. Viral infection is believed to be one of the things that causes the body to make antibodies against platelets.
What can be done to prevent the disease?
There is no known prevention for this disorder.
How is the disease diagnosed?
ITP is diagnosed based on symptoms and results of blood tests. A full blood count identifies low platelet counts. The blood can also be tested for platelet autoantibodies to confirm the diagnosis. A low platelet count is usually the only problem found in blood tests. If these tests do not confirm the diagnosis, a bone-marrow biopsy can be performed. During a bone marrow biopsy, a sample of bone marrow is taken from the body and studied. The bone marrow sample should show normal bone marrow and normal amounts of cells that develop into platelets. Because ITP involves platelet destruction in the bloodstream, the results of the bone-marrow tests should remain normal.
What are the long-term effects of the disease?
Most cases of ITP do resolve. However, some people develop chronic ITP. They may have prolonged episodes of low platelet counts and the complications that go with them.
What are the risks to others?
Although a viral infection is believed to generate the immune response, ITP itself is not contagious.
What are the treatments for the disease?
In some cases, the platelet count returns to normal on its own. In many other cases, corticosteroids, such as methylprednisolone or dexamethasone, are given to quiet the immune response. These can be given either intravenously or as oral tablets.
If steroid therapy does not improve the platelet count, more aggressive interventions can be tried. These include using intravenous immunoglobulin (IVIG). IVIG binds the autoantibodies that are attacking the platelets and removes them from the system. Once they are removed from the bloodstream, they cannot destroy the platelets. This treatment is very expensive and requires intravenous administration of medication.
Finally, the blood can be filtered using a technique called plasmapheresis, which is similar to dialysis in some ways. A large catheter is placed into a blood vessel, and the blood is filtered through the plasmapheresis unit, removing the autoantibodies. This treatment is usually reserved for severe cases of ITP. A splenectomy, or removal of the spleen, can be performed. Often this will cure the condition. Other experimental treatments have been tried with varying results.
What are the side effects of the treatments?
As with any treatment, side effects can be caused by the medications or allergies to them. Complications may also arise from surgery or other treatments for ITP.
What happens after treatment for the disease?
Treatment continues until a normal platelet count is restored. Then, the platelet count is monitored, and treatment can begin again if the platelet count begins to fall.
How is the disease monitored?
ITP is monitored by repeated full blood counts.
Author: Bill Harrison, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Contributors
Potential conflict of interest information for reviewers available on request |
