Myeloproliferative disorders are diseases in which too many of certain types of blood cells — monocytes, platelets, fibroblasts, red blood cells — are made in the bone marrow, the spongy tissue inside the large bones in the body where red and white blood cells and platelets are made.
Chronic Myelomonocytic Leukemia
In patients with chronic myelomonocytic leukemia (CMML), the body increases its production of monocytes (a type of white blood cell) and has difficulty producing normal numbers of other types of blood cells. People with this disease often have symptoms of anemia — fatigue, headache, pallor — and may develop abdominal pain due to enlargement of the spleen. Some have a low white blood count or a low platelet count, and therefore are susceptible to infections or bleeding problems. CMML is classified either as a myeloproliferative disease or a myelodysplastic syndrome and its treatment depends in part on how it manifests itself, but often entails blood transfusions and sometimes oral or intravenous chemotherapy to control the disease.
Essential thrombocythemia (also called primary thrombocythemia), a disease that results in the overproduction of platelets by the bone marrow, generally affects people over 50. (Elevated numbers of platelets can also occur as a result of infection, iron deficiency, and other secondary causes.) Platelets, also known as thrombocytes, prevent bleeding or cause it to stop. High numbers of platelets can result in increased blood clotting or sometimes increased bleeding. Symptoms may include headache, dizziness, tingling in the fingers and toes, bleeding, and enlargement of the spleen. Physicians usually perform a bone marrow biopsy (by inserting a needle into the bone to obtain a sample of marrow for microscopic analysis) to confirm the diagnosis. Treatment includes drugs that slow down platelet production, as well as aspirin and possibly chemotherapy.
Myelofibrosis is a disorder in which fibroblasts, cells that are found in the bone marrow, produce too much fibrous or scar tissue within the bone-marrow space. When this happens, blood-producing cells are produced in fewer numbers and can be destroyed more rapidly, resulting in anemia, low platelet count, and a tendency to develop infections. The disease, which is most common in people between the ages of 50 and 70, often produces few symptoms initially, but when anemia develops, they may include fatigue and weakness and abdominal pain from an enlarged spleen. Myelofibrosis can occur by itself or in association with myeloproliferative diseases such as essential thrombocythemia and polycythemia, or in patients with myelodysplastic syndromes or acute myeloid leukemia. Treatment involves blood cell transfusions to increase the number of red blood cells. Interferon can slow the progression of this disease, and some patients benefit from surgical removal of the spleen. In a few cases, bone marrow transplantation can provide curative therapy.
Polycythemia vera, a disease of the hematopoietic stem cells (cells that give rise to blood cells) is characterized by the overproduction of red blood cells by the bone marrow. This overproduction can lead to thickening of the blood, which can impair the function of the heart or the brain. Symptoms include headache, shortness of breathe, bleeding, or dizziness. Polycythemia vera can also increase the likelihood of developing blood clots. To arrive at an accurate diagnosis, physicians must eliminate from consideration other conditions that mimic polycythemia vera. Treatment includes phlebotomy (removal of one unit of blood) on a regular basis. For some patients, for example for those who have experienced blood clotting, chemotherapy rather than phlebotomy is often used to control the excess production of red blood cells. Interferon can also be used to treat this disease.