Polycythemia vera (PV) is a disorder of the bone marrow, in which you produce too many red blood cells, causing your blood to thicken. You may also have a higher than normal number of white blood cells and platelets. PV is a progressive but often manageable type of blood cancer that is part of a group of disorders collectively known as a myeloproliferative neoplasm (MPN). Here are a few things to know about this rare blood disease. 1. PV develops slowly. Polycythemia vera usually develops over a number of years and you may have it for a long time without noticing signs or symptoms. A diagnosis of polycythemia vera often comes about when it is discovered during blood work for an unrelated condition or test. PV is a chronic disease that restricts blood flow through the vessels. The thicker blood can lead to clots, which may cause stroke and other complications, but with treatment, people can live with the disease for many years. 2. PV is a rare disease usually caused by a defective gene. Slightly more than 50 per 100,000 people in the United States have PV. Researchers discovered in 2005 that, in about 95% of cases, it’s linked to a genetic defect that develops in adulthood. It occurs slightly more often in men than in women, for unknown reasons, and most people who get a diagnosis of PV are over 60. PV is very rare in younger people. 3. You may have no symptoms or a variety of symptoms. You can have PV for years with no symptoms, but when clots begin to block smaller blood vessels, you may have headaches, changes in vision, lightheadedness, night sweats, or gout. Your hands may feel numb or swell and you may also feel itchy, especially after a warm bath or shower. Over time, PV can cause an enlarged spleen, because your spleen filters blood and so the extra red blood cells collect there. An enlarged spleen can make you have a feeling of fullness in the upper left side of your abdomen. In addition to an increased risk of stroke or heart attack, other complications from PV can include myelofibrosis, another progressive bone marrow disorder, which occurs in about 15% of PV patients, and a smaller number of cases will develop acute leukemia. 4. There are effective treatments for managing polycythemia vera. If you have PV, you will be monitored and treated by a hematologist or oncologist. Treatment includes a procedure called a phlebotomy, a safe and simple technique in which blood is removed from your system, similar to giving blood. Phlebotomies may be done as often as once a week when you are first diagnosed, but once your blood count is stabilized, you may only go every few months. Medications for PV can help slow the production of red blood cells or reduce the risk of clots. Novel medications are now available that target the gene defect. Without treatment, polycythemia vera can be life-threatening however, with proper medical care, many people experience few problems. If you have PV, it’s important that you tell your doctors how you are feeling on a regular basis – the treatment plan may change depending on your symptoms. If you are concerned that you may have PV, talk to your healthcare provider about diagnostic tests.