Myelosuppression, otherwise known as bone marrow suppression, is a reduction in the capacity of the bone marrow to generate blood cells. It causes decreased numbers of circulating leucocytes (leucopenia), erythrocytes (erythropenia), neutrophils (neutropenia), and platelets (thrombocytopenia). Decreased leucocytes or neutrophils cause immunosuppression. Decreased erythrocytes or platelets cause hypoxia, fatigue, and an increased tendency to bleed. Depending on the extent to which cell production is reduced, myelosuppression can be mild to severe, or even fatal.
Most chemotherapeutic agents suppress bone marrow function to some degree. The agents associated with severe bone marrow suppression include:
- cytosine arabinoside,
- mitomycin C,
- the nitrogen mustards (including cyclophosphamide, chlorambucil, ifosfamide, melphalan and bendamustine), and
Immunosuppression places the patient at extreme risk of infection. It is the major, dose-limiting, life-threatening side effect of cancer chemotherapy. Nursing staff face a significant challenge in providing the patient with understanding and a supportive environment to withstand this potentially devastating complication.
Signs and Symptoms of Myelosuppression
The signs and symptoms of myelosuppression are largely related to the decrease in the levels of blood components.
- Fever, or other signs of infection, can be caused by leucopenia or neutropenia.
- Excessive bleeding or bruises can be caused by thrombocytopenia.
- Fatigue can be caused by anaemia.
Myelosuppression Causes & Risk Factors
Causes and risk factors for myelosuppression include the following.
Chemotherapy and other cancer treatments are the primary causes of myelosuppression. This is because many of the medicines used in chemotherapy temporarily suppress the bone marrow.
X-rays can have a devastating effect if they reach the bone marrow, particularly when performed over a large proportion of the body or repeated frequently. The radiation disrupts the bone marrow’s function of producing blood cells and platelets.
The cancer cells themselves can also lead to myelosuppression. A number of cancers attack the bone marrow, displacing the cells that it hosts. However, there are other factors that can suppress the bone marrow, without attacking it directly:
- poor nutrition (common in cancer patients),
- gradual decrease in the production of blood cells with age,
- viral infections, and
- several non-chemotherapeutic medications.
The condition usually develops more than a week following damage to the bone marrow. Nevertheless, the bone marrow usually recovers over the next few weeks. Occasionally, there may be permanent damage that causes irreversible myelosuppression. Extremely rigorous radiation, chemotherapy or other cancer treatments can demolish every single cell in the bone marrow.
Diagnostic Tests for Myelosuppression
Laboratory tests used to diagnose myelosuppression include the following.
Blood Count Tests
Having blood drawn for testing is a common experience for cancer patients. As myelosuppression is a side effect of chemotherapy, regular blood tests are an important part of routine treatment. A significant decrease in red blood cells, white blood cells or platelets should be reported to the doctor immediately. Many laboratory tests are required to establish counts of red blood cells, leucocytes, neutrophils and platelets, and to examine the clotting function of the patient’s blood. Initially, anaemia may be detected using a complete blood count. This is a routine test that calculates the number and relative proportions of all the different types of cells in the blood stream.
Bone Marrow Biopsy
When a complete blood count proves inconclusive, the doctor may suggest a bone marrow biopsy. This test also determines the presence of cancer cells in the bone marrow caused by leukemia or other bone marrow cancers. This test is done by aspirating bone marrow cells from the part of the pelvis known as the ischium. The aspiration is extremely painful, so the patient requires support throughout the procedure.
Management of myelosuppression involves treatment of both its causes and symptoms. A mild case of myelosuppression does not always require active management.
Limiting Cancer Therapy
If the case is caused by chemotherapy or radiation therapy, the doctor will consider stopping, reducing or postponing the treatment. This is done to reduce damage and to give the patient’s bone marrow time to recover. In these cases, the full dose of the cancer treatment may not be given.
Meanwhile, red blood cells and platelets can be simply replaced by blood transfusions of packed red blood cells or platelets. This provides a short-term solution to the problem, but the treatment may need to be repeated because the transfused cells have a short life cycle. There is also a small risk of a transfusion reaction and infection if the donor blood is contaminated by a virus. Transfusions of white blood cells are not normally given because, unfortunately, they are not particularly effective.
Growth Factor Therapy
Injections of growth factor may be successful. Growth factor is a substance, naturally produced by the body, which stimulates the bone marrow to produce blood cells. There are specific types of growth factor for each type of blood cell:
- granulocyte colony-stimulating factor,
- granulocyte-macrophage colony-stimulating factor, and
Growth factor injections can reduce the need for blood transfusions and improve life for cancer patients. However, they have several side effects if the kidneys are healthy, and may not be successful if the body is already producing sufficient erythropoietin. Other side effects include bone pain, rashes, sore muscles, nausea, fever, fluid retention, tachycardia, red eyes and dyspnoea.
A bone marrow transplant is required when the bone marrow has sustained permanent, severe damage. Bone marrow is harvested from compatible donors.
Complications of myelosuppression may include the following.
Severe infection, caused by a very low level of white blood cells, may eventually lead to systemic infection.
Thrombocytopenia, or low platelet count, causes poor platelet aggregation. This will eventually lead to profuse bleeding in all areas of the body including nosebleeds, hemochezia (bright red blood in the stools) and severe bruising.
Unmanaged myelosuppression often leads to a severe reduction in red blood cells, also known as anaemia. This results in excessive weakness, tiredness, difficulty of breathing and hypoxia.
Prevention of Myelosuppression
Prevention of myelosuppression depends on limiting or avoiding the causes.
- Use chemotherapeutic agents cautiously.
- Avoid exposure to high doses of radiation.
- Fortify the immune system with a healthy diet, exercise and vitamin supplements.