Dear Doctor Column, December 23, 2002

Question:

My father has been diagnosed with idiopathic thrombocytopenic purpura. He has had three episodes within the past 6 months where his platelet levels have dropped to less than 3,000. So far, he has been treated with steroids. If the steroids fail to work long term, we've been told that the only other course of treatment is surgery to remove his spleen. Are there any other options available for treating this condition, which we still know very little about?

Answer:

Idiopathic thrombocytopenic purpura (ITP) is characterized by an abnormal decrease of a certain type of blood cell called thrombocytes, or more commonly platelets, (thrombocytopenia), without a readily apparent cause or underlying disease. The disorder is characterized by abnormal bleeding into the skin. Blood specialists, known as hematologists, are experts in the diagnosis and treatment of this disorder.

Platelets are colorless, disc-shaped cells that circulate constantly in the blood. If damage occurs to a blood vessel, platelets rush to the scene to begin forming a blood clot to plug the damaged vessel and stop the bleeding. In healthy people, the bone marrow constantly replenishes platelets, which generally live about 10 days. If the platelet count drops to extremely low levels, bleeding can occur with the slightest trauma or even without injury. When the number of platelets drop sufficiently, extensive bruises or a distinctive rash, composed of red pin-point lesions called petechia, develop. Other signs can include unexplained nosebleeds, excessive bleeding from the gums, blood in the stools, heavy menstrual periods, or prolonged bleeding during dental or surgical procedures.

Thrombocytopenia is divided into two types — idiopathic and secondary. Idiopathic is the medical term for unknown cause. However, scientists now know that most cases of idiopathic thrombocytopenia are caused by the spleen and lymph nodes producing substances called antibodies that attack and destroy platelets. This condition also is known as autoimmune thrombocytopenic purpura — autoimmune because the antibodies are part of the person's own immune system and turn against the body, attacking the platelets. Purpura comes from the Greek word for purple, the color of the bruises that result from the bleeding beneath the skin that low platelets can cause.

Secondary thrombocytopenia means the low platelet count is secondary to some other disease or process. In addition, a number of drugs can trigger an immune system reaction that can destroy platelets. The other general category of secondary thrombocytopenias include conditions that interfere with the bone marrow's production of platelets. Common causes of this type of secondary thrombocytopenia include viral infections, such as measles or chickenpox, and a variety of drugs, especially anticancer drugs.

The treatment of ITP is determined by the severity of symptoms. In some patients, particularly children, the platelet count recovers spontaneously, usually within the first few weeks. Other chronic ITP patients (about 5% to 10%) have stable disease, with a platelet count of 30,000 to 100,000, which may persist for months to years and rarely requires treatment. Of patients who need treatment (platelet count consistently less than 25,000 to 30,000), approximately 75% are cured of their disease with either corticosteroids or by removal of their spleen (splenectomy).

Other drugs, such as vincristine, azathioprine, danazol, cyclophosphamide, and cyclosporine are prescribed for patients only in the most severe cases where other treatments have not shown benefit, since these drugs have potentially harmful side effects. Platelet transfusions usually are not beneficial and are seldom performed. Because all therapies carry risks, it is important that over treatment (treatment based solely on platelet counts and not on symptoms) be avoided.

Experimental treatments currently under study for ITP include bone marrow or blood stem cell transplantation and the cancer drug rituximab, which belongs to a new group of cancer drugs known as monoclonal antibodies.

More information about ITP is available from the National Organization for Rare Disorders www.rarediseases.org and the National Institutes of Health http://www.niddk.nih.gov/health/hematol/pubs/itp/itp.htm