Polycythemia rubra vera, now more commonly called polycythemia vera (PV), is an abnormal proliferation of the bone marrow cells that develop into red blood cells, white cells, and/or platelets.
All of the cells produced by the bone marrow — that is red cells, the white cells known as granulocytes, and platelets — are produced by cells derived from a single type of bone marrow cell, called a stem cell. Stem cells are undifferentiated cells with the potential to develop into any one of the three different cell types mentioned. They are present in every normal person’s bone marrow and develop into red cells, granulocytes, or platelets, depending on which cells are needed by the body and the stimuli that they receive. In polycythemia, an early precursor cell, perhaps a stem cell, starts developing without the normal stimulus, producing excessive numbers of the three cell types.
The excess production of red cells is usually the most obvious manifestation of PV, but both granulocytes and platelets are generally produced in excess amounts, and high counts of these cells are helpful in making the diagnosis.
The cause of the condition is not known. Since other diseases can cause high red-cell counts, such as some forms of chronic heart or lung disease, and occasionally kidney tumors, PV can only be diagnosed by ruling out these other causes. If one of those other diseases is present, the polycythemia is referred to as secondary polycythemia.
PV usually begins in late middle age and has a slowly progressive course. Although the uncontrolled proliferation of the cells meets the definition of a tumor, the condition is not considered a malignancy, and the complications of PV arise from the high cell counts in the blood, not from metastases or uncontrolled local growth of tumor cells as happens with most malignancies. In a small percentage of cases, PV can evolve into a leukemia, which is malignant and often fatal.
PV is not infectious, and one cannot catch it from someone who has it. In early cases the disease is simply controlled simply by removing blood on a frequent basis, which reduces the number of blood cells in the body. Iron pills or vitamins with iron should not be taken. If this treatment is insufficient, an anticancer drug called hydroxyurea is often used to suppress the excess production of cells. Most patients with PV will survive with treatment for 15 or more years, and since most are in late middle age when they develop the disease, life expectancy is not greatly reduced by PV.
The most common complication and cause of death is thrombosis, which can produce heart attacks, transient ischemic attacks, strokes, or deep-vein thromboses leading to emboli to the lungs. Treatment to keep the red cell and platelet counts near normal will usually prevent such thromboses.
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