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Benign Hematologic (Blood) DisordersA collaborative project of the Arizona Telemedicine Program, the Arizona Health Sciences Library and the Arizona Cancer Center.
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Myeloproliferative Disorders
A. What Are the Myeloproliferative Disorders?
In the myeloproliferative disorders, the bone marrow cells proliferate uncontrollably. Examples of these disorders are polycythemia vera, essential thrombocythemia, and myelofibrosis with myeloid metaplasia. The diseases are rare and usually occur in patients between 50 and 60 years of age.
The disorders arise from a change in the DNA of a single bone marrow cell. This change causes the cell to replicate uncontrollably. While the causes of such changes are uncertain, possible risk factors include exposure to radiation and familial history of the disorder.
The different disorders affect specific cells in the marrow. Polycythemia vera affects the red blood cells (RBCs); essential thrombocythemia affects the megakaryocyte (cells that produce platelets); and myelofibrosis with myeloid metaplasia affects the megakaryocytes and fibroblasts (connective tissue cells).
B. Polycythemia Vera
Polycythemia vera is a kind of myeloproliferative disorder involving the erythrocytes, or red blood cells (RBCs). The RBCs carry oxygen to the body. They are produced in the bone marrow and removed from the blood by the spleen. In polycythemia vera, the number of RBCs in the blood becomes too high. Please see Erythrocytosis/Polycythemia.
Polycythemia vera, like the other myeloproliferative disorders, is caused by changes in the DNA of a single bone marrow cell. In polycythemia vera, this leads to uncontrolled RBC proliferation. Risk factors include exposure to radiation, some cancer therapy medications (myelosuppressive agents), and familial history of polycythemia vera.
Polycythemia vera usually occurs in patients over 50 years of age. Possible symptoms include easy bruisability, purpura (purplish areas on the skin), reddish skin, blood in the stool, blood clots, headaches, fatigue, and an enlarged and tender spleen. Therefore, patients may have both difficulties with clotting and with bleeding.
Polycythemia vera is diagnosed by patient history, physical examination for signs of the disease, and laboratory tests, especially blood studies. The disorder is usually treated by phlebotomy, removal of RBCs from the blood using a needle. Treatment may also include medications such as hydroxyurea, chlorambucil, anagrelide, and aspirin.
C. Essential Thrombocythemia
In essential thrombocythemia (ET), the megakaryocyte levels in the bone marrow become elevated. The megakaryocytes are the bone marrow cells responsible for producing platelets. They are large cells that do not normally leave the marrow. In ET, their proliferation causes an increase in the platelets in the blood. See Thrombocytosis.
Like the other myeloproliferative disorders, ET is caused by a change in DNA in a single cell (in this case, a megakaryocyte). Patients with ET will usually have no symptoms. If symptoms do result, they include itchy skin and an enlarged spleen.
In ET patients, platelets may clump together in the blood to form a thrombus, a clot blocking normal blood flow. A thrombus blocking an important blood vessel could result in death. If platelet levels become markedly elevated, the formation of thrombi is common and is the most dangerous threat of the disease. Patients with ET should avoid cardiovascular risk factors such as smoking and alcohol, as these habits increase the likelihood of thrombus formation. Symptoms of thrombotic episodes include recurrent or transient headaches, confusion, visual disturbances, seizures, and partial paralysis on one side of the body. Bleeding may also occur in the skin or after injury, but it is rarely a problem.
ET is diagnosed by patient history, physical examination, and laboratory testing of blood and bone marrow. Diagnosis especially focuses upon distinguishing ET from the other myeloproliferative disorders. Treatment involves plateletpheresis, therapy with radioactive phosphorus, and medications such as melphalan, busulfan, aspirin, dipyridamole, anagrelide and alpha-interferons. Patients with ET have the same life expectancy as unaffected patients.
D. Myelofibrosis with Myeloid Metaplasia
In myelofibrosis with myeloid metaplasia (MMM), the megakaryocyte levels in the bone marrow become elevated. The megakaryocytes are the bone marrow cells responsible for producing platelets. They are large cells that do not normally leave the marrow. Their proliferation leads to abnormalities in the bone marrow such as anemia (decreased red blood cells), changes in platelet counts (they may be increased, normal or decreased), and increased numbers of fibroblasts, or hard connective tissue in the marrow.
Symptoms of MMM include enlarged liver and spleen and signs of anemia, such as pallor, weakness, elevated heart rate, and shortness of breath (please see Anemia). Later in the disease, patients may experience fever, weight loss, and bone pain.
Treatment involves red blood cell transfusion in cases of anemia. Androgens (such as Danazol), low doses of chemotherapy drugs such as Busulfan, Hydroxyurea, Thioguanine, alpha-interferons, glucocorticoids such as Hydrocortone or Hydrocortisone, radioactive phosphorous, and folic acid supplements may also be administered. If the spleen is enlarged and painful, it may be removed in a splenectomy.
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Updated: October 30, 2000