Polycythemia vera (PV) is an extremely rare blood disorder (five cases per million persons) which causes the red blood count to be much higher than normal. For persons with PV, the production of red blood cells goes into overdrive causing the body to produce more red blood cells than is healthy for the average person.
The affect of the presence of these extra red blood cells is that the blood actually thickens, causing it to flow more slowly. As a result of the slower blood flow, you may be more prone to experience blood clots or blocked arteries and veins. This disorder may also lead to angina, heart failure or heart attack and stroke.
PV has also been known to lead to the enlargement of the liver and spleen, stomach ulcers, kidney stones, gout, myelofibrosis (bone marrow replaced by scar tissue) and acute myelogenous leukemia (AML).
PV is a slow acting disease and a person may have undiagnosed PV for years before symptoms present themselves. According to the National Heart Lung and Blood Institute, when symptoms do present themselves, they include: “headaches, dizziness, itching, and vision problems such as blurred or double vision.” In addition, persons may experience unusual bleeding around the gums or from small cuts. Fatigue, weight loss and difficulty breathing or shortness of breath may also be symptoms of PV. There is also a tendency for the spleen to enlarge so persons with PV may also experience “feelings of pressure or fullness on the left side of the abdomen.” (NHLBI)
Types of polycythemia:
There are two main types of PV, polycythemia vera (primary polycythemia) and secondary polycythemia. Each of these two types of polycythemia are caused by different stimuli.
Primary Polycythemia:
Primary polycythemia is caused by a mutation in the JAK2 gene (the JAK2 V617F mutation). More than 90% of persons with PV possess the JAK2 gene mutation. The JAK2 gene supplies the body with a special protein that actually tells the red blood cells to grow. When the JAK2 gene mutates, the red blood cells grow –- and grow –- and grow. The cause of the JAK2 gene mutation isn’t known.
Primary polycythemia tends to run in families. However, it is not believed to be an inherited disorder. It is believed that the JAK2 gene may be more prone to mutation in some familiars than others. At one time, PV was thought to affect persons of Jewish descent more than other ethnicities but it is now believed that persons of all ethnicities are equally affected. It is slightly more common in men than women and in persons over the age of 60.
Secondary Polycythemia:
Unlike primary polycythemia which is caused by a mutation of the JAK2 gene, secondary polycythemia is caused by exposure (over long periods of time) to oxygen levels which are too low (such as which might be found at high-altitudes). Low oxygen levels stimulate the production of erythropoietin (EPO). EPO is a naturally occurring hormone. When the levels of EPO are too high, you body will begin to manufacture more red blood cells. The result of the presence of the additional red blood cells is the same in secondary polycythemia as in primary polycythemia –- the blood thickens.
Persons live at high altitudes are more likely to develop secondary polycythemia. In addition, person who smoke or who have heart or lung disease may be at an increased risk of developing secondary polycythemia.
Treatment:
Primary PV is incurable but can generally be managed with proper care, disease management and treatment. Treatment options include:
• Phlebotomy - A procedure which removes blood from body in order to lower the number of red blood cells and bring levels to normal;
• Hydroxyurea - Cancer medication which causes a reduction in red blood cells;
• Interferon-alpha – A treatment that signals causes your immune system to attack the defective bone marrow cells which are over-producing red blood cells; and
• Radiation – A treatment to suppress bone marrow which is hyperactive.
Sources:
Polycythemia Vera, National Heart Lung and Blood Institute, Feb 2009, http://www.nhlbi.nih.gov/health/dci/Diseases/poly/poly_whatis.html
Polycythemia vera, The Mayo Clinic, 02 Apr 2009, http://www.mayoclinic.com/health/polycythemia-vera/DS00919