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Polycythemia vera

Polycythemia is a condition in which there is a net increase in the total circulating erythrocyte (red blood cell) mass of the body. There are several types of polycythemia. more...

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Types

Primary polycythemia (also known as polycythemia vera)

Primary polycythemia, often called polycythemia vera (PCV), polycythemia rubra vera (PRV), erythremia, or just PV, occurs when excess erythrocytes are produced as a result of a proliferative abnormality of the bone marrow. This can also be brought on by abnormalities (tumors) in the kidneys or other growths since the kidney helps to regulate erythrocytes production. Often, excess white blood cells (leukocytosis) and platelets (thrombocytosis) are also produced. It is, therefore, classified as a myeloproliferative disease.

In primary polycythemia there may be 8 to 9 million and occasionally 11 million erythrocytes per cubic millimeter of blood, and the hematocrit may be as high as 70 to 80%. In addition, the total blood volume sometimes increases to as much as twice normal. The entire vascular system can become markedly engorged with blood, and circulation times for blood throughout the body can increase up to twice the normal value. The increased numbers of erythrocytes can increase the viscosity of the blood to as much as five times normal. Capillaries can become plugged by the very viscous blood, and the flow of blood through the vessels tends to be extremely sluggish.

Recently, in 2005, a mutation in the JAK2 kinase (V617F) was found by multiple research groups (Baxter et al., 2005; Levine et al., 2005) to be strongly associated with polycythemia vera. JAK2 is a member of the Janus kinase family. This mutation be helpful in making a diagnosis or as a target for future therapy.

As a consequence of the above, people with untreated PV are at a risk of various thrombotic events (deep venous thrombosis, pulmonary embolism), heart attack and stroke, and have a substantial risk of Budd-Chiari syndrome (hepatic vein thrombosis). The condition is considered chronic; no cure exists. Symptomatic treatment (see below) can normalize the blood count and most patients can live a normal life for years.

Secondary polycythemia

Secondary polycythemia is caused by either appropriate or inappropriate increases in the production of erythropoietin that result in an increased production of erythrocytes. In secondary polycythemia their may be 6 to 8 million and occasionally 9 million erythrocytes per cubic millimeter of blood. A type of secondary polycythemia in which the production of erythropoietin increases appropriately is called physiologic polycythemia. Physiologic polycythemia occurs in individuals living at high altitudes (4275 to 5200 meters), where oxygen availability is less than at sea level. Such people may have 6 to 8 million erythrocytes per cubic millimeter of blood. It is because of this that Lance Armstrong trains in the mountains to prepare for bicycle races.

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Treatment of polycythemia vera - Tips - Author Abstract
From American Family Physician, 10/1/03 by Chuck Carter

Polycythemia vera (PV) is one of three chronic myeloproliferative disorders, along with essential thrombocythemia and myelofibrosis with myeloid metaplasia. The incidence of PV is 2.3 per 100,000 patients, and the median age at diagnosis is 60 years. Tefferi recommends treatment options for PV.

Polycythemia describes an increase in red blood cell mass. The increase in red blood cell mass may be caused by an actual increase in red blood cell mass (true polycythemia) or a spurious laboratory value (apparent polycythemia). True polycythemia is classified as either primary or secondary. Primary polycythemia is caused by a myeloproliferation and is not mediated by excess erythropoietin. In contrast, secondary polycythemia can be caused by an external source, such as "smoker's polycythemia," or an internal disorder, such as renal cancer. Erythropoietin levels in secondary polycythemias vary depending on the etiology.

PV can have life-threatening complications, including stroke and evolution into either myelofibrosis with myeloid metaplasia or acute leukemia. Treatment is directed according to patient risk stratification. Frequent phlebotomy and chemotherapy are the cornerstones of treatment. Hematocrit levels should be maintained below 45 percent in white men and 42 percent in women and blacks. Chemotherapy using hydroxyurea, busulfan, or pipobroman is indicated for high-risk patients. (Pipobroman is not available in the United States.) Interferon-alfa is another chemotherapeutic option for reducing red blood cell burden and treating PV-associated pruritus.

Non-life-threatening sequelae include microvascular complications and aquagenic pruritus. Microvascular complications may appear clinically as headache, light-headedness, transient neurologic abnormality, transient ocular disturbance, tinnitus, atypical chest pain, paresthesias, and erythromelalgia (a rare but painful burning sensation of the hands or feet). Low-dose aspirin (81 mg or less per day) can be used to treat these disorders. Aquagenic pruritus is a generalized body itching often brought on by a hot bath. Treatment options include either selective serotonin reuptake inhibitors or interferon-alfa.

Tefferi A. Polycythemia vera: a comprehensive review and clinical recommendations. Mayo Clin Proc February 2003;78:174-94.

COPYRIGHT 2003 American Academy of Family Physicians
COPYRIGHT 2003 Gale Group

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