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May 15, 2006
Myeloproliferative Disorders: Polycythemia vera
by SirGan|
There are six diseases included in the group of myeloproliferative disorders and this group includes chronic:
This group is characterized by production of too many of certain types of blood cells are made in the bone marrow.
Polycythemia vera (PV) is a disease in which body makes too many red blood cells, which makes blood too thick. It could be also described as an abnormal increase in blood cells-primarily red blood cells, resulting from excess production by the bone marrow. The overproduction of red blood cells is most dramatic, but production of white blood cells and platelets is also elevated in most cases. Polycythemia vera is a rare myeloproliferative disorder and it is estimated to occur, in approximately 1 in 100,000 individuals. Polycythemia Vera is primarily affects middle-aged or elderly people. It occurs more frequently in men than women, and rarely in patients under 40 years old. It is not known what causes Polycythemia vera.
Synonyms:
Bone marrow functionsBone marrow is the body's blood-forming organ and it contains blood-forming cells called "hematopoeitic precursor or stem cells". These cells have two important functions.
Normal bone marrow is composed of a family of hematopoeitic clones all reproducing themselves and forming daughter cells that will, in turn, develop into red blood cells, white blood cells and platelets. The normal marrow also balances production of different cell types so they appear in the blood in their proper proportions. When something disturbs this balance- you get all kinds of cells disproportions in blood. Polycythemia vera is one of these disproportions!
Possible causes of Polycythemia veraAlthough, the exact cause of Polycythemia vera is still unknown-several evidences are indicating that the etiology could be in unregulated neoplastic proliferation.
Although the causative genetic events are yet to be found, two key aspects of the biology can identify it:
Symptoms of Polycythemia veraIn most cases, affected individuals may experience:
In some cases, individuals with Polycythemia vera experience itching (pruritus), especially after a hot bath. Affected individuals often have an abnormally enlarged spleen (splenomegaly) and/or liver (hepatomegaly). In some cases, affected individuals may have associated conditions including:
Types of Polycythemia veraPrimary polycythemia (also known as polycythemia vera)This type occurs when erythrocytes are produced as a result of a proliferative abnormality of the bone marrow. This doesn’t have to mean that the problem is in the bone marrow because it can also be brought on by tumors in the kidneys since they help to regulate erythrocytes production.
Findings: There may be 8 to 9 million and occasionally 11 million erythrocytes per cubic millimeter of blood. A normal range for adults is 4-5! Hematocrit, complete volume of blood cells, 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 filled with blood. 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.
Secondary polycythemiaSecondary polycythemia is caused by increases in the production of erythropoietin that result in an increased production of erythrocytes.
Findings: There may be 6 to 8 million and occasionally 9 million erythrocytes per cubic millimeter of blood.
Physiologicpolycythemia: A type of secondary polycythemia in which the production of erythropoietin increases appropriately. It occurs in individuals living at high altitudes (4275 to 5200 meters), where oxygen availability is at much smaller concentration than at sea level. Such people may have 6 to 8 million erythrocytes per cubic millimeter of blood.
Other causes of secondary polycythemia include
Relative polycythemiaRelative polycythemia is an apparent rise of the erythrocyte level in the blood but the problem isn't in bone marrow or erythropoietin but, underlying cause is reduced blood plasma. It can be caused by burns, dehydration and stress polycythemia.
Diagnosis of polycythemiaWhile the diagnosis could be made simply based on blood counts, most doctors- hematologists follow the guidelines of the Polycythemia Vera Study Group and run certain diagnostic tests. If the Study Group findings are present, then a diagnosis can be made with certainty.
Category A
Category B
The major diagnostic issue related to PV is distinguishing it from other forms of erythrocytosis, which are more common than PV.
The criteria that must be met for a diagnosis of polycythemia vera and the incidence of these abnormalities at diagnosis are a demonstration of increased red cell mass combined with an:
enlarged spleen (splenomegaly) which is presenting 75% of cases or any two other features of pluripotential precursor cell involvement, such as:
ComplicationsMain mechanism is that the increased blood volume and increased circulating red cell mass play a key role in the symptoms and complications experienced in cases of uncontrolled polycythemia vera.
ThrombosisThrombosis may be arterial (coronary, cerebral, peripheral vascular) or venous (involving peripheral, hepatic or portal veins). Small vessel insufficiency produces cyanosis (slightly bluish, grayish or dark purple discoloration), pain in fingers and toes, or gangrene of the digits.
HemorrhageMild hemorrhagic phenomena such as nosebleeds, bleeding gums and easy bruisability are common. There could be some even more serious problems with bleeding such as:
TreatmentBecause the condition cannot be cured, treatment focuses on treating symptoms and reducing thrombotic complications reducing the erythrocyte levels.
PhlebotomyBloodletting or phlebotomy is one form of treatment, which often may be combined with other therapies. The purpose of phlebotomy is to reduce the red blood cell mass -that is, the total number of circulating red blood cells, and to do it fairly quickly, at least in the beginning when the hematocrit is high.
ChemotherapyThis form of therapy for polycythemia may be used sparingly, when the rate of bloodlettings required to maintain normal hematocrit is not acceptable.
Other therapies include
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