(Idiopathic Thrombocytopenic Purpura; Immune Thrombocytopenic Purpura; ITP)
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 disease.
Platelets are cell fragments that circulate in the bloodstream and help blood clot (see also Overview of Platelet Disorders). The blood usually contains about 140,000 to 440,000 platelets per microliter. When the platelet count falls below about 50,000 platelets per microliter of blood, 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 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, the supply cannot keep up with the demand.
In adults, ITP is usually long lasting (chronic), but in children ITP often resolves on its own.
Symptoms of immune thrombocytopenia may develop suddenly or gradually and subtly.
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). 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.
Bleeding worsens as the number of platelets decreases. People who have very few platelets may lose large amounts of blood into the digestive tract or may develop life-threatening bleeding in the brain even though they have not been injured.
Doctors make the diagnosis of ITP when the platelet count is less than 100,000 per microliter of blood without a similar decrease in the red blood cell or white blood cell count, and when there is no other clear explanation for thrombocytopenia such as an infection, or use of certain drugs. 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. Microscope examination is crucial in distinguishing ITP from thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS). TTP and HUS are other disorders that can cause thrombocytopenia. Rarely, a sample of bone marrow is removed and examined under a microscope (bone marrow biopsy and aspiration) to provide information about platelet production.
In ITP, the antibodies that destroy platelets can be blocked temporarily with a corticosteroid (for example, prednisone) or intravenous immune globulin, allowing the number of platelets to increase. Children usually recover within several weeks to months after this treatment.
Some adults recover during the first year, but most do not. Adults who do not respond adequately to corticosteroids may require additional drugs that suppress the immune system, including rituximab, azathioprine, or mycophenolate.
Some adults (but not children) with ITP eventually require surgical removal of the spleen (splenectomy) to increase the number of platelets. A downside to splenectomy is an increased risk of certain life-threatening infections. People who undergo splenectomy may be given certain antibiotics or vaccines that lessen (but do not eliminate) this risk.
Newer drugs, called thrombopoietin-receptor agonists (such as romiplostim and eltrombopag), increase the rate of platelet production and may be effective for years. These drugs are especially useful for people who are not able to undergo (or are unwilling to undergo) splenectomy.