Myeloproliferative disorders are a group of rare illnesses that cause blood cells in the bone marrow, including red blood cells, white blood cells, and platelets, to grow and develop abnormally. Bone marrow is the soft, spongy tissue found inside bones.
There are four major types of myeloproliferative disorders: chronic myelogenous leukemia, essential thrombocytosis, myelofibrosis, and polycythemia vera.
Chronic myelogenous leukemia (CML): Chronic myelogenous leukemia is a cancer of the bone marrow. It occurs when the bone marrow produces abnormal granulocytes (a type of white blood cell). The white blood cells are usually produced normally at first, but they are not able to fully mature and allow new cells to replace them. Normally, white blood cells help fight against diseases and infections. In patients with CML, these white blood cells are unable to function properly. Over time, the white blood cells overcrowd healthy blood cells. Eventually, the bone marrow may become damaged and stop producing white blood cells normally. All of these factors lead to an increased risk of bleeding and developing infections. CML is considered a chronic condition because it usually progresses much slower than acute leukemia.
Essential thrombocytosis: Essential thrombocytosis occurs when the body produces too many platelet cells. These cells help the blood clot in order to stop bleeding. When there is too much clotting in the body, small blood vessels may become clogged. As a result of excessive clotting, blood flow is limited or completely blocked through blood vessels. Depending on where the blockage occurs, the condition may be fatal. For instance, if arteries in the heart are blocked, it may lead to a heart attack.
Myelofibrosis: Myelofibrosis, also called myelosclerosis, occurs when the bone marrow produces too much collagen or fibrous tissue. As a result, fewer blood-producing cells are created, and they can be destroyed more rapidly, which leads to anemia (low levels of red blood cells), low platelet count, and an increased risk of developing infections. This condition can occur by itself or in combination with other myeloproliferative disorders, such as essential thrombocytosis or polycythemia vera.
Polycythemia vera: Polycythemia vera occurs when the bone marrow produces too many blood cells, especially red blood cells. This condition may cause the blood to become thicker than normal, which can impair the functions of vital organs, such as the brain or heart.
The cause of myeloproliferative disorders remains unknown, although some researchers believe that genetics and exposure to certain chemicals, radiation, and electrical wiring may play a role.
Myeloproliferative disorders are serious medical conditions. Complications of these disorders may be fatal. A person's survival rate depends on the type of myeloproliferative disorder he/she has, as well as the severity of his/her illness. For instance, myelofibrosis may lead to death within three to six years. On average, people with CML live about four to five years after diagnosis. However, if CML progresses into acute leukemia, the average survival rate is only three months. People with other, less severe types of myeloproliferative disorders can often live much longer, especially if they are diagnosed in the early stages of the disease. People with polycythemia vera live an average of 10-20 years after diagnosis. People with primary thrombocytosis generally have a normal life expectancy with only a low risk of developing cancer.
Although there is no cure for myeloproliferative disorders, treatment may help patients live several years after they are diagnosed.
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