Immune thrombocytopenia (ITP) is a bleeding disorder caused by decrease in the number of platelets (thrombocytes) that occurs in a person who does not have another disorder that affects platelets. In ITP, the immune system produces antibodies against a person's own platelets and destroys them.
People may have tiny purple spots on their skin (petechiae) and bleed easily.
Diagnosis is with blood tests to measure the number of platelets.
Corticosteroids or other drugs are given to block the destruction of platelets.
Some people benefit from drugs that increase platelet production.
In adults, doctors sometimes remove the person's spleen.
(See also Overview of Platelet Disorders and Overview of Thrombocytopenia.)
Platelets are cells that are made in the bone marrow and circulate in the bloodstream and help blood clot. The blood usually contains about 140,000 to 440,000 platelets per microliter (140 to 440 × 109 per liter ). When the platelet count falls below about 50,000 platelets per microliter of blood (less than 50 × 109 per liter), bleeding can occur even after relatively minor injury. The most serious risk of bleeding, however, generally does not occur until the platelet count falls below 10,000 to 20,000 platelets per microliter (10 to 20 × 109 per liter) of blood. At these very low levels, bleeding may occur without any recognized injury.
Immune thrombocytopenia is a disorder in which antibodies form and destroy the body's platelets. Why the antibodies form is not known; however, in children, ITP often occurs after a viral infection. Although the bone marrow may increase platelet production to compensate for the destruction, usually the supply cannot keep up with the demand. Sometimes the antibody that is destroying the platelets also attacks the bone marrow and reduces the production of platelets.
In adults, ITP is usually long lasting (chronic). In children, ITP often resolves on its own.
Symptoms of ITP
Some people may not have symptoms of immune thrombocytopenia. In other people, bleeding symptoms may develop suddenly or gradually. With chronic ITP, fatigue is common.
Bleeding in the skin may be the first sign of a low platelet count. Many tiny red dots (petechiae) often appear in the skin on the lower legs, and minor injuries may cause black-and-blue bruises (ecchymoses or purpura). The gums may bleed, and blood may appear in the stool or urine. Menstrual periods or nosebleeds may be unusually heavy. Bleeding may be hard to stop.
DR P. MARAZZI/SCIENCE PHOTO LIBRARY
By permission of the publisher. From Deitcher S. In Atlas of Clinical Hematology. Edited by JO Armitage. Philadelphia, Current Medicine, 2004.
DR P. MARAZZI/SCIENCE PHOTO LIBRARY
DR P. MARAZZI/SCIENCE PHOTO LIBRARY
By permission of the publisher. From Deitcher S. In Atlas of Clinical Hematology. Edited by JO Armitage. Philadelphia, Current Medicine, 2004.
DR P. MARAZZI/SCIENCE PHOTO LIBRARY
Bleeding worsens as the number of platelets decreases. People who have very few platelets may lose large amounts of blood into their digestive tract or may rarely develop life-threatening bleeding in their brain even though they have not been injured. Headache and other nervous system symptoms can occur with bleeding inside the brain.
Diagnosis of ITP
Blood tests to measure platelet count and clotting
Tests to rule out other disorders that cause a low platelet count and bleeding
Doctors make the diagnosis of immune thrombocytopenia (ITP) when the platelet count is less than 100,000 per microliter of blood (less than 100 × 109 per liter) without a similar decrease in the number of red blood cells or white blood cells, and when there is no other clear explanation for thrombocytopenia such as an infection or use of certain drugs (see table Causes of Thrombocytopenia). There is no well-established test to confirm that a person has ITP.
The platelet count may be measured with an automated counter to determine the severity of thrombocytopenia, and a sample of blood must be examined under a microscope to provide clues to its cause. Doctors need to examine blood under a microscope to distinguish ITP from thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS). TTP and HUS are other disorders that can cause thrombocytopenia by destroying platelets.
Rarely, a sample of bone marrow is removed and examined under a microscope (bone marrow biopsy and aspiration) to provide information about platelet production.
Treatment of ITP
Corticosteroids
Sometimes, removal of the spleen
Rarely, platelet transfusions
Some adults (but usually not children) with ITP benefit from surgical removal of the spleen (splenectomy). Because the spleen removes abnormal platelets from the bloodstream, removing the spleen sometimes increases the number of platelets. Downsides to splenectomy include an increased risk of blood clots, increased risk of cancer, and increased risk of certain life-threatening infections such as pneumococcal infections. People who undergo splenectomy may be given certain antibiotics or vaccines that lessen (but do not totally eliminate) the infection risk. Drug treatment is increasingly being used instead of splenectomy.
People with life-threatening bleeding may be given a platelet transfusion (in addition to intravenous corticosteroid and/or immune globulin).
