Bone Marrow Disorders
Various conditions and diseases can affect the structure and function of the bone marrow. The following is a list of some of these. For additional details on symptoms, tests and treatment, use the links to go to the articles on each condition.
Leukemia is a cancer of the white blood cells (WBCs) that can affect any of the five WBC types. Leukemia can be acute or chronic and may involve the myeloid cells (neutrophils, monocytes, basophils and their precursors) or lymphocytic cells. It begins with one abnormal cell that begins to continuously replicate (clone) itself. The resulting leukemic cloned cells do not function normally. They do not fight infections and, as they accumulate, they inhibit the production of normal WBCs, red blood cells (RBCs) and platelets. People with leukemia may have frequent infections, fatigue, bleeding, bruising, anemia, night sweats, and bone and joint pain. The spleen, which filters the blood and removes old cells, may become enlarged, as may the liver and lymph nodes.
Myeloproliferative disorders (MPDs) or myeloproliferative neoplasms (MPNs) are diseases centered in the bone marrow and characterized by the overproduction of one type of immature blood cell and the mature cells that are derived from the precursor.
With MPDs, excess production of a cell's precursor leads to an increased number of that type of cell in the bone marrow and the blood. This can be associated with an increase or decrease in the number of other blood cells, which may be inhibited and crowded out. This leads to symptoms related to blood cell overproduction, shortages, and dysfunction throughout the body.
MPDs or MPNs are classified by the type of cells that overgrow in bone marrow. Common MPD subtypes include:
- Chronic myeloid leukemia: overgrowth of granulocytes (neutrophils and precursors)
- Polycythemia vera: overgrowth of red blood cells and precursors
- Essential thrombocythemia: overgrowth of platelets (thrombocytes) and precursors
Myelodysplastic Syndrome (MDS) is a group of diseases characterized by abnormal bone marrow cell production. Frequently with MDS, the marrow appears to be productive, but not enough normal mature blood cells are being made (ineffective production). This leads to symptoms of anemia, infection, and/or excessive bleeding and bruising. MDS syndromes are classified partially by how the cells in the bone marrow and in circulation look under the microscope and include:
- Anemia, low neutrophil count (neutropenia) and/or thrombocytopenia that do not respond to treatment (refractory)
- Abnormal cell appearances (so-called dysplasia) in one or more than one cell lines
- Increase in immature precursors (blasts) in the marrow, with risk of evolving to acute myeloid leukemia
Chromosome analysis (cytogenetic) provides additional information for diagnosis and outcome prediction. Over time, MDS can progress to acute myeloid leukemia.
- Aplastic anemia – a defect in a stem cell or injury to the bone marrow results in the loss of cell precursors (usually RBC). Some cases of aplastic anemias are caused by radiation or exposure to chemicals such as benzene or certain drugs. A few are due to rare genetic abnormalities such as Fanconi's anemia or associated with an acute viral illness such as human parvovirus. The cause is unknown for about half of the cases.
- Anemias caused by nutritional deficiencies such as iron, folate, vitamin B12, chronic infection or inflammation, and/or hemoglobin abnormalities (hemoglobinopathies) that result in abnormally shaped or sized RBCs.
- Some types of anemia are caused by a deficiency or dysfunction of erythropoietin, a chemical produced by the kidneys that stimulates the bone marrow to produce RBCs. A lack of erythropoietin can lead to decreased red cell production by the bone marrow.
- Infections, certain drugs, toxins, and cancer can affect the bone marrow, resulting in anemia.
Plasma cell disorders (such as multiple myeloma) are conditions associated with an overproduction of one clone of a fully mature (terminally differentiated) B lymphocyte called a plasma cell. A plasma cell's primary function is to produce antibodies – targeted immunoglobulin proteins that help protect the body against infections. Normally, plasma cells are produced as needed. Sometimes, a plasma cell may become malignant and begin to divide uncontrollably, generating numerous copies of itself (clones) that form tumors in the bone marrow and crowd out other types of normal cells.