Myelosuppression is a decrease in the production of blood cells. Normal blood contains large numbers of cells, including red blood cells to carry oxygen and white blood cells to fight infections. The blood also contains platelets, tiny cell fragments that initiate blood clotting. These cells and fragments are made in the bone marrow, a reddish substance found in the centers of some bones. Healthy bone marrow makes large numbers of red blood cells, white blood cells, and platelets each day to replace those that wear out. In myelosuppression, the bone marrow makes too few of these cells.
A decrease in the number of red blood cells, called anemia, is very common in cancer patients. A drop in white blood cell numbers is often a problem during chemotherapy. One type of white blood cell, called a neutrophil, is usually affected most severely. A decrease in these cells is called neutropenia. Because neutrophils are responsible for defending the body against bacteria, neutropenia increases the chance of an infection. Thrombocytopenia, a drop in the number of platelets in the blood, is more rare; platelet numbers become low enough to cause problems in less than 10% of cancer patients.
Myelosuppression is a painless condition, but the decreases in important blood cells can result in fatigue, an increased risk of infections, or excessive bleeding. The consequences vary from mild to life-threatening, depending on how low the blood cell numbers fall.
Causes
The most common cause of myelosuppression is cancer treatment. Many of the drugs used in chemotherapy temporarily suppress the bone marrow. Therapeutic x rays that reach the bone marrow are also destructive. Cancer cells can also cause myelosuppression. Some cancers invade the bone marrow and crowd out the cells normally found there. Others can suppress the bone marrow without invasion. Nutritional deficiencies, common in cancer patients, also slow blood cell production as do viruses and some non chemo drugs.
Myelosuppression usually starts seven to ten days after an injury to the bone marrow. However, the bone marrow generally returns to normal within the next few weeks. Less often, cumulative damage can be caused. Occasionally, irreversible damage causes permanent myelosuppression. Very intensive chemotherapy or radiation can destroy all of the cells in the bone marrow.
Treatments
Myelosuppression is not always treated, especially if it is mild.
If the myelosuppression is a result of chemotherapy or radiation therapy, the cancer treatments may be stopped, delayed, or reduced to give the bone marrow a chance to recover. This may mean that the full dose of the treatment is not received.
Red blood cells or platelets can be replaced by transfusions, packed red blood cells, or platelets. These treatments can be very effective in the short term; however, the transfused cells are short-lived and the treatment may need to be repeated. There is a small chance of a transfusion reaction and a slight risk of infection by a virus carried in the blood. Transfusions of white blood cells are ineffective and rarely given.
Injections of growth factors may also be effective. Growth factors are chemicals, found naturally in the body, that stimulate the bone marrow to make blood cells. Each type of growth factor affects specific blood cells. Several are being manufactured as drugs. They include erythropoietin, granulocyte colony-stimulating factor (G-CSF or filgrastim), granulocyte-macrophage colony-stimulating factor (GM-CSF or sargramostim), and interleukin 11 (oprelvekin). Erythropoietin injections stimulate red blood cell production. They can decrease the need for a transfusion and improve the quality of life. This drug has few side effects if the kidneys are healthy, but it may not be effective if the body is already making enough natural erythropoietin. G-CSF and GM-CSF can speed the return of neutrophils. Their side effects include bone pain, fevers, rashes, muscle pains, and nausea. Interleukin 11 can increase platelet numbers. Its side effects may include fluid retention, a rapid heartbeat, red eyes, and difficulty breathing. Growth factors are expensive and several injections are usually needed.
Complete destruction of the bone marrow is incompatible with life. If the bone marrow is severely damaged, a bone marrow transplant may be necessary.
Alternative and complementary therapies
Supportive therapy can help to minimize the effects of myelosuppression. If nutrition is a contributing factor, iron or vitamin supplements may be beneficial. Antibiotics can aid in preventing infections. Some patients find that mild exercise and enjoyable distractions help with fatigue.
—A growth factor that stimulates the bone marrow to make neutrophils and some other types of white blood cells. It is also known as sargramostim or molgramostim.
Growth factor
—A chemical that stimulates body cells to grow or make more cells. Growth factors are found naturally in the body, but can also be manufactured and used as drugs.
Interleukin 11 (IL-11)
—A growth factor that stimulates the bone marrow to make platelets. It is also known as oprelvekin.
Neutropenia
—Too few neutrophils in the blood.
Neutrophil
—A type of white blood cell that destroys bacteria.
Packed red blood cells
—Blood that has had the fluid portion (plasma) removed.
Platelets
—Tiny fragments of cells that begin the blood clotting process. They are found in the blood.
Red blood cells
—The cells in the blood that carry oxygen.
Thrombocytopenia
—Too few platelets in the blood.
Transfusion
—A transfer of blood or blood products from one person to another.
Transfusion reaction
—An allergic reaction to some of the cells or proteins in another person's blood.
White blood cells
—The cells in the blood that fight infections. There are several types of white blood cells.
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