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Polycythemia vera is a disorder of the blood-producing cells of the bone marrow that results in overproduction of red blood cells.
In polycythemia vera, the excess of red blood cells increases the volume of blood and makes it thicker, so that it flows less easily through small blood vessels.
Polycythemia vera occurs in about 2 in every 100,000 people. The average age at which the disorder is diagnosed is 60, and it rarely occurs in people younger than 20. More men than women develop polycythemia vera, but the difference is slight.
The cause is often unknown, but more than 95% of people with polycythemia vera have a mutation in the gene called JAK2 . This mutation causes excess cell production. Blood cells are normally produced in the bone marrow. Sometimes the spleen and liver also start producing blood cells. Eventually, the bone marrow becomes scarred and less able to produce blood cells.
Often, people with polycythemia vera have no symptoms for years. The earliest symptoms usually are
Vision may be distorted, and people may have blind spots or see flashes of light. Bleeding from the digestive tract or gums and more bleeding than would be expected from small cuts may occur. The skin, especially the face, may look red. People may itch all over, particularly after bathing or showering. People may have redness and burning sensations in the hands and feet. More rarely, bone pain may be felt.
Sometimes the first symptoms are due to a blood clot. A clot may form in almost any blood vessel, including those of the arms, legs (causing deep vein thrombosis), heart (causing a heart attack), brain (causing a stroke), or lungs. Blood clots may also block blood vessels that drain blood from the liver ( Budd-Chiari syndrome).
In some people, the number of platelets (cell-like particles that help the body form blood clots) in the bloodstream increases. An increase in the number of platelets can lead to abnormal blood clotting (see Thrombocythemia), but the platelets may not function normally, which can cause bleeding.
The liver and spleen may enlarge as both organs begin to produce blood cells. The spleen also enlarges as it removes red blood cells from the circulation. As the liver and spleen enlarge, a sense of fullness in the abdomen may develop. Pain can suddenly become intense should a blood clot develop in blood vessels of the liver or spleen.
The excess of red blood cells may be associated with other complications, including stomach ulcers, gout, and kidney stones. Rarely, polycythemia vera progresses to leukemia.
Polycythemia vera may be discovered through routine blood tests done for another reason, even before people have any symptoms. The level of the protein that carries oxygen in red blood cells (hemoglobin) and the percentage of red blood cells in the total blood volume (the hematocrit) are abnormally high. The number of platelets and white blood cells may also be increased.
Doctors consider polycythemia vera a possibility if the hematocrit is very high. However, the diagnosis cannot be based solely on the hematocrit result. Once the increased red blood cell mass (polycythemia) is discovered, doctors must determine whether the person has polycythemia vera or polycythemia caused by some other condition (secondary polycythemia). The medical history and examination may help differentiate between polycythemia vera and secondary polycythemia, but doctors must usually investigate further. People are usually tested for the JAK 2 gene mutation.
Blood levels of erythropoietin , a hormone that stimulates the bone marrow to produce red blood cells, also may be measured. Levels of erythropoietin are extremely low in polycythemia vera, but they are often, but not always, normal or high in secondary polycythemia. Rarely, cysts in the liver or kidneys and tumors in the kidneys or brain produce erythropoietin ; people with these conditions have high levels of erythropoietin and may develop secondary polycythemia.
Without treatment, survival with polycythemia vera is less than two years. With treatment, survival can be prolonged in some but not all cases to more than two decades.
Treatment does not cure polycythemia vera, but it does control it and can decrease the likelihood of complications, such as the formation of blood clots. The aim of treatment is to decrease the number of red blood cells. Usually, blood is removed from the body in a procedure called phlebotomy, similar to the way blood is removed when donating blood. Up to a pint of blood is removed every other day until the hematocrit reaches a normal level. Then blood is removed as needed to maintain the hematocrit at a normal level, for example, every few months.
Because phlebotomy may increase the number of platelets and does not reduce the size of an enlarged liver or spleen, people who undergo phlebotomy may need drugs to suppress production of red blood cells and platelets. Hydroxyurea, a chemotherapy drug, is frequently given, but when used for many years there is concern that it may increase the risk of transformation to leukemia, although this risk has not been proven. Alternative drugs for lowering the number of platelets, such as interferon-alpha and anagrelide, are sometimes used in younger people who may need treatment for long periods. Baby aspirin has been proven to decrease the risk of blood clots. New drugs are being tested.
Other drugs can help control some of the symptoms. For example, antihistamines can help relieve itching, and aspirin can relieve burning sensations in the hands and feet as well as bone pain.
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