Myeloproliferative neoplasms (MPNs) are a group of rare diseases in which the bone marrow produces too many blood cells. A genetic change in the myeloid cell line leads to unrestrained proliferation of red blood cells, platelets or certain types of white blood cells.
The specific kind of MPN depends on what type of blood cell is over-produced. Cases are divided into low, intermediate and high risk based on several factors. Only 6,000 people are diagnosed with an MPN in the U.S. every year. The risk of developing an MPN increases with age.
Polycythemia vera (PV) is the overproduction of red blood cells. Patients with PV often have no symptoms, and their disease is discovered when they have a blood test for some other reason. Common symptoms include itching, headache, dizziness and difficulty concentrating. The main complication of PV is blood clotting. Most patients eventually develop myelofibrosis (see below) and many progress to acute myeloid leukemia. Although PV is an incurable disease, it does not usually affect normal lifespan.
Treatment for PV focuses on preventing blood clots. All patients receive low-dose aspirin to thin the blood and periodic phlebotomies to reduce the percentage of red cells in their blood. Patients with high-risk disease also receive hydroxyurea, a medication that reduces the risk of clotting.
Essential thrombocythemia (ET) is the overproduction of platelet cells. Symptoms can include headache and visual complaints, but many patients do not experience any symptoms at all. Because patients with ET have high levels of platelets, they have a higher risk of blood clots. However, the disease can also lead to higher risk of bleeding. ET is almost twice as common in women as in men. It does not generally affect normal lifespan.
Patients with low-risk ET receive daily low-dose aspirin to reduce the risk of blood clots. Patients with high-risk disease receive aspirin plus hydroxyurea to lower platelet counts.
Myelofibrosis (MF) is the build-up of scar tissue within bone marrow. When scar tissue forms within bone marrow, the marrow becomes less able to make blood cells. As a result, the body begins to produce blood cells in the spleen. This causes the spleen to enlarge, causing abdominal pain and a feeling of early fullness when eating. In addition, many patients experience fatigue, fevers and night sweats and suffer from anemia. Many patients with polycythemia vera or essential thrombocythemia eventually develop myelofibrosis. MF can also develop out of chronic myeloid leukemia, acute myeloid leukemia or myelodysplastic syndromes.
For patients with low-risk disease, treatment focuses on alleviating symptoms. For patients with high-risk disease (or intermediate-risk disease and spleen-related symptoms) treatment can include targeted drug therapies. Other therapy options can include radiation to the spleen, immunotherapy, steroids and hydroxyurea. Stem cell transplant is an option for a small percentage of patients.