What is Myelosuppression and Why is it Important?

Consequences of Chemotherapy Induced Myelosuppression

Photo of bone marrow
What is the meaning of myelosuppression?. istockphoto.com

Definition: Myelosuppression

Myelosuppression is defined as a decrease in the ability of the bone marrow to produce blood cells.  It occurs most commonly with cancer as a side effect of chemotherapy, but there are other causes as well.

Cells Affected in Myelosuppression

Myelosuppression can result in decreased production of:

  • Red blood cells (RBCs) 
  • White blood cells (WBCs)
  • Platelets

Hematopoiesis, Bone Marrow, and Myelosuppression

To understand myelosuppression it's helpful to talk about the function of bone marrow.

In the bone marrow, all of the blood cells—red blood cells, white blood cells, and platelets—begin with a single cell type: the hematopoietic stem cell.

Hematopoietic stem cells have the ability to evolve into any type of blood cell. These cells go down separate pathways as they differentiate into red blood cells, platelets, and white blood cells, and then into more specialized cells such as the different types of white blood cells. But they all begin with stem cells. Myelosuppression refers to a process that disrupts these stem cells, and. consequently, affects all of the different types of blood cells. The term myeloablation refers to severe myelosuppression in which no blood cells are made.

What Causes Myelosuppression

There are several ways in which the bone marrow can be disrupted so that it does not produce blood cells.

  • Damage to the stem cells - The most common cause of myelosuppression is due to medications which slow the ability of stem cells and specialized descendants to divide and multiply. All of our blood cells are continuously being replenished. Medications such as chemotherapy drugs cause drug-induced bone marrow suppression.
  • Replacement of the bone marrow/crowding - The bone marrow may be "crowded out" by things such as blood cancers or metastatic cancer so that there is not "room" for the normal manufacturing of blood cells.
  • Bone marrow failure - Instead of being suppressed by a medication, the bone marrow can instead be destroyed by various toxins and chemicals. When this is the case, stopping the drug will not result in the bone marrow again doing its job of manufacturing blood cells.

    Specific Causes of Myelosuppression

    Processes which can cause myelosuppression include:

    • Chemotherapy-induced bone marrow suppression. Chemotherapy kills off all rapidly dividing cells such as cancer cells, including the cells which become all of the types of blood cells.
    • Cancers of the bone marrow such as leukemias, lymphomas, myeloma, metastatic cancer to the bone marrow can result in "crowding" so there is not room for hematopoiesis to take place.
    • Deliberate myelosuppression/myeloablation - In blood-related cancers present in the bone marrow, very high dose chemotherapy is used to ablate the bone marrow. When the bone marrow is "clear" a bone marrow transplant or peripheral blood stem cell transplant is then done to repopulate the bone marrow with non-cancerous blood stem cells.

    Deficiencies of Blood Cells

    When stem cells aren't growing and dividing and specializing into the unique types of blood cells (when there is bone marrow suppression or myelosuppression) deficiencies in the type of blood cells are called:

    • Anemia - Anemia refers to a deficiency of red blood cells. Anemia can cause fatigue, weakness , pallor, a rapid heart rate, shortness of breath, and lightheadedness. Chemotherapy-induced anemia is a common cause of fatigue during chemotherapy.
    • Leukopenia - Leukopenia refers to a deficiency of white blood cells. With leukopenia people run the risk of infection, so symptoms may be symptoms of infections such as fever, cough, and pain with urination. With cancer, most often people will hear about chemotherapy-induced neutropenia. Neutrophils are the type of white blood cell that is our first line of defense again infections with bacteria, viruses, and fungi (and against cancer cells as well.)
    • Thrombocytopenia - Thrombocytopenia refers to a deficiency of platelets. A low level of platelets can result in bruising and heavy bleeding. Chemotherapy-induced thrombocytopenia may not be a problem as often as say neutropenia but can cause serious bleeding in some people.

    Is Myelosuppression the Same as Immunosuppression?

    You may wonder if immunosuppression and myelosuppression are the same. In the setting of myelosuppression, the production of white blood cells is decreased, so there will be immunosuppression. But immunosuppression doesn't always mean myelosuppression. For example, a medication (or another process) may suppress white blood cells or other particular parts of the immune system, but not affect the red blood cells or platelets.

    Treatment of Myelosuppression

    The treatment of myelosuppression will involve treating whatever the cause of myelosuppression happens to be. If it is related to drugs or chemotherapy, treatments may have to be stopped or delayed. If it is due to infiltration of the bone marrow, and consequent crowding, treatment of the cancer in the bone marrow is the most important step. If it is due to bone marrow failure, it will be important to see whether or not the bone marrow failure is reversible, and if not, treatments such as replacement of the blood cells and bone marrow transplant may need to be considered.

    For symptoms related to myelosuppression, treatments may be directed at the specific cell deficiency causing symptoms. For anemia, transfusions, iron supplements, or growth factors may be given. For neutropenia resulting in a risk of infection or presence of an infection, growth factors (such as Neulasta) may be used and the infection treated aggressively with combination antibiotics. For low level of platelets which raises the risk of bleeding transfusion may be needed.

    The links above to chemotherapy-induced anemia, neutropenia, and thrombocytopenia outline these specific treatments that may be considered if myelosuppression is related to chemotherapy.

    Also Known As: Bone marrow suppression

    Examples: Due to severe myelosuppression, Rick's oncologist suggested he wait a week before his next chemotherapy treatment.

    Sources:

    Coates, T., Drug-Induced Neutropenia and Agranulocytosis. UpToDate. Updated 08/01/16.

    Weinzierl, E., and D. Arber. The Differential Diagnosis and Bone Marrow Evaluation of New-Onset-Pancytopnia. American Journal of Clinical Pathology. 2013. 139(1):9-29.

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