Summary
Polycythemia vera (PV) is a rare, chronic condition in which the bone marrow produces too many blood cells (myeloproliferation). The bone marrow is the soft tissue inside bones where blood cells are made. In PV, the body makes too many red blood cells, and many people also have higher than normal numbers of white blood cells and platelets.
Because red blood cells are produced in excess, the number of red blood cells circulating in the bloodstream becomes abnormally high. This can cause the blood to become thicker and increase in volume, a condition known as hyperviscosity. Thicker blood may not flow as easily through small blood vessels, which can affect normal circulation.
People with PV may experience a range of symptoms. These can include headaches, fatigue, weakness, dizziness, itching of the skin (especially after warm baths or showers), and an enlarged spleen (splenomegaly). Some people may also have digestive problems. In addition, PV increases the risk of developing blood clots, which can block blood flow to important organs.
More than 90% of people with PV have a change (variant) in the JAK2 gene. Treatment includes phlebotomy, a procedure that removes blood from the body to reduce the number of red blood cells, along with medications to help control blood cell production and reduce complications.
Introduction
PV was first reported in medical literature in 1892. At that time, and for many years after, doctors grouped PV with similar conditions under the term “myeloproliferative disorders” (MPDs). This term was first used to describe polycythemia vera and related disorders in 1951. These were diseases in which the bone marrow made too many blood cells.
In 2008, the World Health Organization reclassified MPDs to “myeloproliferative neoplasms” (MPNs) to reflect the consensus that these diseases are blood cancers (neoplasms). MPNs are characterized by the overproduction (proliferation) of one or more of the three main blood cell lines, red or white blood cells or platelets. Red blood cells carry oxygen to the body. White blood cells fight infection. Platelets are involved in clotting blood in response to injury.
In addition to PV, three other disorders are commonly classified as MPNs, chronic myeloid leukemia, essential thrombocythemia, and primary myelofibrosis. Because MPNs involve uncontrolled growth of blood-forming cells, they are also considered a form of blood cancer.
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