It is a rare disorder, occurring more frequently in men, and is rarely seen in those under 40 years old. Its cause is unknown, and the disease is considered a hematologic malignancy . The disease develops slowly, usually after the age of 50 or 60 and may progress to acute myelogenous leukemia . The viscosity of the blood and the increased platelets result in a high potential for clot formation, which can result in stroke or heart attack . In some patients, hemorrhage occurs because, although the platelets responsible for blood clotting are present in high numbers, their clotting ability is impaired.
Risk factors are unknown, but the incidence is highest among people of Jewish ancestry.
Symptoms are due to increased blood viscosity and clotting. Phlebotomy is one method used to reduce the high blood viscosity. Occasionally, chemotherapy may be given to suppress the bone marrow. The median survival is 11 to 15 years. Polycythemia may convert to a type of leukemia .