Problems in the Bone Marrow

Stem cells are immature or unspecialized cells that can develop into different types of cells. They remain unspecialized until signaled by the body to change. They replace cells that are worn out, damaged, or diseased. Some disorders, such as aplastic anemia, myelodysplastic syndrome, and myeloproliferative disorders, affect stem cells in the bone marrow and thus interfere with the production of red blood cells, white blood cells, and platelets.

In aplastic anemia, the bone marrow does not have enough stem cells and thus cannot produce enough red and white blood cells and platelets. Aplastic anemia is relatively rare but is more common among older people. Aplastic anemia is commonly caused by malfunction of the body's immune system, causing the body to attack its own tissues (autoimmune disorder). Other causes include exposure to radiation and use of certain chemotherapy drugs, the antibiotic chloramphenicol, and drugs used to treat seizures (anticonvulsants). Sometimes the cause is unknown. People with aplastic anemia must be treated immediately, or they will die. Transfusions are given and may have to be continued indefinitely. Stem cell or bone marrow transplantation can cure aplastic anemia, but older people can rarely withstand this taxing treatment. Drugs that may help include corticosteroids, such as prednisone, and drugs that suppress the immune system (immunosuppressants), such as antithymocyte globulin and cyclosporine. Drugs that stimulate production of the blood's components may be used: a synthetic version of erythropoietin or darbepoietin for red blood cells, colony-stimulating factors for white blood cells, and thrombopoietin for platelets.

In myelodysplastic syndrome, the bone marrow has enough stem cells, but they do not mature normally into red blood cells, white blood cells, and platelets. Myelodysplastic syndrome affects mostly older people. Usually, its cause is unknown, but it can be caused by use of certain drugs or alcohol or by toxic substances in the environment, such as lead. Erythropoietin, given by injection, is sometimes useful. It increases the blood cell count.

In myeloproliferative disorders, the immature cells (called stem cells) that develop into blood cells or platelets increase too much, or the fibrous tissue that supports the cells increases too much. Primary thrombocythemia, polycythemia vera, and myelofibrosis are myeloproliferative disorders. In a few people, a myeloproliferative disorder progresses or transforms into a cancer such as leukemia.