Idiopathic Thrombocytopenic Purpura

Idiopathic thrombocytopenic purpura (ITP) is a bleeding disorder in which the blood does not clot as it should. The bleeding is due to a low number of platelets, blood cells that help the blood clot and stop bleeding. People with ITP often have purple bruises that appear on the skin. The bruises mean that bleeding has occurred in small blood vessels under the skin.

The words idiopathic, thrombocytopenic, and purpura mean:

• Idiopathic means that the cause of the disease or disorder is not known.
• Thrombocytopenic means there is a lower-than-normal number of platelets in the blood.
• Purpura are purple bruises where bleeding occurs just under the skin.

Types of ITP

There are two types of ITP: acute (temporary or short-term) ITP and chronic (long-lasting) ITP.

• Acute ITP generally lasts less than 6 months. It mainly occurs in children, both boys and girls, and is the most common type of ITP. It typically occurs following an infection caused by a virus. This type of ITP often goes away on its own within a few weeks or months and does not return. Treatment may not be needed.
• Chronic ITP is a long-lasting (6 months or longer) type of ITP that mostly affects adults. However, some teenagers and even younger children get this type of ITP. Chronic ITP affects women two to three times more often than men. Treatment depends on how severe the bleeding symptoms are and the platelet count. In mild cases, treatment may not be needed.

Symptoms

The signs and symptoms of idiopathic thrombocytopenic purpura (ITP) are related to increased bleeding due to low numbers of platelets.

Signs include:

• Bruising (purpura): purplish areas on the skin or mucus membranes (such as in the mouth) due to bleeding. The bruises may occur for no apparent reason.
• Petechiae: pinpoint red spots on the skin (typically the legs) that often occur in groups and may look like a rash. The spots are due to bleeding under the skin.
• Bleeding that is hard to stop.
• Bleeding from gums (for example, when dental work is done).
• Nosebleeds.
• Heavy menstrual bleeding in women.
• Blood in the urine.
• Blood in the stool (bowel movement).

Diagnosis

To diagnose idiopathic thrombocytopenic purpura (ITP), doctors use your medical history, a physical exam, and blood tests that usually include:

• A complete blood count, to show the numbers of different kinds of blood cells, including platelets, in a small sample of your blood.
• A blood smear, which involves placing some of your blood on a slide. A microscope is then used to look at your platelets and other blood cells.

A blood smear is important to be sure that the platelet count is correct. In healthy people, the platelet count can be falsely low, since the chemical used in the tube during blood collection may cause platelet clumping.

If blood tests show that you have a low number of platelets, you may need additional tests to help with the diagnosis. For example, bone marrow tests may be used to see if enough platelets are being formed in the bone marrow.

In ITP, the red and white blood cell counts are normal.

Causes

In idiopathic thrombocytopenic purpura (ITP), the immune system treats a person's own platelets as if they were invaders in the body, attacking and destroying them. The immune system attacks platelets by making proteins called antibodies. The antibodies bind to platelets (attach) and then are removed by the spleen (an organ that is part of the immune system and helps fight infection).

Normally, the immune system makes antibodies to fight off germs or other harmful things (called antigens) that enter the body. The reason why the immune system decides to attack platelets is not known.

Children who get the acute (temporary) type of ITP often have had a recent viral infection. It is possible that the infection somehow "triggers" or sets off the immune reaction that leads to ITP in these children. ITP in adults, on the other hand, does not seem to be linked to infections.

Because "idiopathic" means "of unknown cause," a better name for most cases of ITP is immune thrombocytopenic purpura.

Reference:

National Heart, Lung, and Blood Institute, USA.