Bone Marrow Diseases

Common bone marrow diseases are leukemias, or cancers of the white blood cells; anemias, or the inability to produce enough red blood cells; genetic disorders; environmentally provoked diseases; and the spread of other cancers such as lymphomas. They can be caused by genetic or environmental factors, or a combination of the two.

Bone marrow is a fatty, spongy tissue inside some of the hollow bones of the body. Three major sites of bone marrow are the hip, sternum, and thigh bones. Bone marrow is the location of the blood stem cells, which semi-differentiate into cell types that can then become one of the several types of blood cells. The three types of blood cells are the red and white blood cells and the platelets, which are important in blood clots.

There are five types of white blood cells; if any of these cells becomes abnormal and divides too rapidly, a leukemia results. The problem with a leukemia is that the excessive white blood cells do not serve their typical function of fighting infections; rather, they crowd the other cells, preventing growth and differentiation of functional red and white blood cells, and platelets.

If the bone marrow produces too many red blood cells, the blood can become too thick to travel normally through the blood vessels. Small blood vessels can become clotted. As a result, the brain may not receive enough oxygen, causing a stroke, or portions of the heart may become oxygen starved and die, causing a heart attack. This scenario is a rare disease called polycythemia vera. When a semi-differentiated stem cell becomes abnormally prevalent over the other types, there can be too much of a particular blood cell type. As in leukemia, this blood cell type causes overcrowding in the marrow, and thus inhibits the growth and differentiation of the remaining types of blood cells. This type of disorder is called a myeloproliferative disorder. One example of a myeloproliferative disorder is thrombocythemia, or the overproduction of blood cells, primarily that of platelets.

The opposite type of disorder is called myelodysplastic syndrome (MDS). In MDS, not enough of a certain type of blood cell is made. If too few red blood cells are produced, the result is anemia. If too few white blood cells are made, infections could result due to the reduced protection from the diminished white blood cells. If too few platelets are made, bleeding disorders such as hemorrhaging or excessive nosebleeds may result because the body is unable to form sufficient blood clots. In the case of too few white blood cells, symptoms of leukemia may also result. In fact, unchecked MDS often progresses into acute myeloid leukemia.

A distinct disorder resulting in too few red blood cells is aplastic anemia. In this case, not enough red blood cell progenitor cells are developed in the marrow. The cause of this under development may be an injury to the bone marrow, an alteration in the bone marrow environment that is hostile to red blood cell precursors, or a genetic disorder. Sometimes the cause is human parvovirus. In many cases, the cause is unknown.

...