(Essential Thrombocythemia; Primary Thrombocythemia)
Thrombocythemia is a disorder in which excess platelets are produced, leading to abnormal blood clotting or bleeding.
Platelets (thrombocytes) are normally produced in the bone marrow by cells called megakaryocytes. In thrombocythemia, megakaryocytes increase in number and produce too many platelets.
Thrombocythemia affects about 2 to 3 of 100,000 people. It usually occurs in people older than 50 and more frequently in women. The cause of thrombocythemia is sometimes a genetic mutation, including mutations in the JAK2, myeloproliferative leukemia (MPL), or calreticulin genes.
Thrombocythemia may be
Primary, that is, caused by no other disorder
Secondary, that is, caused by an underlying disorder
Often, thrombocythemia does not cause symptoms. However, an excess of platelets can cause blood clots to form spontaneously, blocking the flow of blood through blood vessels, especially smaller ones but also in large vessels, including vessels in the brain, liver, and heart. Older people with thrombocythemia are much more likely to form clots than are younger people.
Symptoms are due to the blockage of blood vessels and may include
Redness and warmth of the hands and feet, often with burning pain
Tingling and other abnormal sensations in the fingertips, hands, and feet
Loss of vision or seeing spots
Bleeding, usually mild (such as nosebleeds, easy bruising, slight oozing from the gums, or bleeding in the digestive tract)
The spleen and liver may enlarge.
Doctors make a diagnosis of thrombocythemia on the basis of the symptoms and after finding increased platelets during routine screening of the blood. Blood tests, including genetic tests, are done. In addition, microscopic examination of the blood may reveal abnormally large platelets, clumps of platelets, and fragments of megakaryocytes.
To distinguish primary thrombocythemia, whose cause is unknown, from secondary thrombocythemia, which has a known cause, doctors look for signs of other conditions that could increase the platelet count. Removal of a sample of bone marrow for examination under a microscope (bone marrow biopsy) is sometimes helpful.
Small doses of aspirin, which makes platelets less sticky and impair clotting, may be given to help relieve mild symptoms such as redness and warmth of hands and feet, and headache.
Thrombocythemia may also require treatment with a drug that decreases platelet production. Such drugs include hydroxyurea, anagrelide, and interferon-alpha.
Treatment with one of these drugs is typically started when clotting complications develop, when the person is older (for example, age 60 or older), or both. The age of the person, the other risks present, and previous history of forming blood clots (thrombosis) determine the need for such treatment. The drug is continued until the platelet count falls into a safe range. The dose must be adjusted to maintain an adequate number of platelets and other circulating cells.
If drug treatment does not slow platelet production quickly enough, it may be combined with or replaced by platelet exchange, a procedure reserved for emergency situations. In this procedure, blood is withdrawn, platelets are removed from it, and the platelet-depleted blood is returned to the person. Rarely, stem cell transplantation (bone marrow transplantation) is done if a person is young, has a compatible donor, and other treatments have been unsuccessful.