An Overview of Myelosuppression

Myelosuppression, or bone marrow suppression, is defined as a decrease in the ability of the bone marrow to produce blood cells. This may result in a lack of red blood cells (anemia), white blood cells (leukopenia), and platelets (thrombocytopenia). Myelosuppression may occur when the stem cells in the bone marrow are damaged (such as by chemotherapy drugs), when it is crowded (by tumor cells or fibrosis), or due to bone marrow failure.

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.

The term myeloablation refers to severe myelosuppression in which no blood cells are made.

Cells Affected in Myelosuppression

Myelosuppression can result in decreased production of:

Red Blood Cells (RBCs)

Red blood cells contain hemoglobin, the protein that is responsible for binding with and delivering oxygen to all of the tissues of the body.

White blood cells (WBCs)

White blood cells are our body's defense against microorganisms such as bacteria, viruses, and fungi, as well as cancer cells.

Platelets

Platelets are responsible for helping blood to form a clot when a blood vessel is broken.

Myelosuppression vs. 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.

Pancytopenia

Pancytopenia is another confusing term, and is usually caused by myelosuppression. The term "pancytopenia" refers to inadequate numbers of all the types of blood cells, red blood cells, white blood cells, and platelets.

Symptoms

The symptoms of myelosuppression depend on the underlying cause, the level of deficiency of blood cells, and more.

Low red blood cells counts can lead to fatigue, lightheadedness, weakness, pale skin and nail beds, a rapid heart rate, and shortness of breath. Since red blood cells carry oxygen in the blood to different parts of the body, a low number can also cause symptoms similar to obstruction of a blood vessel, such as angina.

Low white blood cell counts raise the risk of infections. Symptoms are primarily those related to the different types of infections such as a fever or chills, cough, redness around incisions or sores, diarrhea, or pain with urination.

Low platelet counts can result in bleeding. Symptoms may include bruising, nosebleeds, heavy menstrual periods, blood in the urine or stools, or wounds that won't stop bleeding.

Causes

There are several ways in which the bone marrow can be disrupted so that it does not produce blood cells, but these can be broken down into three major categories:

• Damage to the stem cells
• Crowding of the bone marrow
• Bone marrow failure

Regardless of the method, the result is that fewer blood cells are formed. Sometimes the cause of myelosuppression is very obvious, such as when a person is receiving chemotherapy, and sometimes it is much less clear, and further tests are need to determine which category is involved and then the specific disorder.

Damage to Stem Cells

The most common cause of myelosuppression is medications that 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. Chemotherapy kills off all rapidly dividing cells such as cancer cells, including the cells which become all of the types of blood cells.

This type of myelosuppression is usually reversible if the medication causing myelosuppression is stopped.

Replacement of the Bone Marrow/Bone Marrow Crowding

The bone marrow may instead 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. Cancers of the bone marrow such as leukemias, lymphomas, myeloma, metastatic cancer to the bone marrow (such as from breast cancer and other solid tumors can result in "crowding" so there is not room for hematopoiesis to take place.

The bone marrow may also be crowded by the presence of scar tissue (fibrosis) in conditions such as myelofibrosis.

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.

Deliberate myelosuppression/myeloablation is sometimes used as a cancer treatment. 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 healthy, noncancerous 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. In addition to the symptoms noted above, an inadequate number of red blood cells can lead to decreased oxygen in the blood and tissues (hypoxia) potentially leading to tissue death (such as in a heart attack).

Leukopenia

Leukopenia refers to a deficiency of white blood cells. With cancer, most often people will hear about 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. Thrombocytopenia, in turn, can be classified as mild, moderate, or severe.

Diagnosis

The diagnosis of myelosuppression will depend on many factors. In the case of chemotherapy-induced myelosuppression, the cause is often obvious. In other cases, a careful history, physical exam, and imaging studies will likely be done, but laboratory analysis is often the mainstay of diagnosis.

This usually begins with a complete blood count to look at the numbers of each type of blood cell. Blood cell indices (such as MCV, MCHC, RDW, reticulocyte count, and MPV) can give further information about the size, shape, and survival of blood cells (for example, if they are not being made or are instead being broken down). A peripheral blood smear for morphology can provide further information describing the types of cells seen and any abnormalities.

A bone marrow evaluation (aspiration and/or biopsy) is often the next step, and can give direct information as to the quality of the bone marrow, for example, if it is being replaced by scar tissue or cancer cells.

A number of other tests may be done to further clarify any findings or look for causes.

Treatment

The treatment of myelosuppression including addressing the underlying cause(s), raising levels of blood cells when needed, and treating symptoms related to the deficiencies.

Treatment of Causes

Treating the underlying cause - when possible - can often resolve the abnormalities, but may take time. . 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.

Treatment of Low Blood Counts

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, Neupogen, or Ryzneuta) may be used and the infection treated aggressively with combination antibiotics. For a low level of platelets which raises the risk of bleeding, transfusion may be needed.

If chemotherapy is being used, treatment may need to be delayed until blood counts are restored to adequate levels.

Coping and Prevention

Sometimes low blood counts do not require treatment, yet there are still things you can do to increase your risk. These lifestyle measures are wise even if your low counts are being treated.

For anemia: Getting slowly (to avoid fainting), pacing yourself throughout the day, do some light exercise every day, talk to your healthcare provider about coping with fatigue related to cancer or your underlying condition.

For leukopenia: Avoiding crowds, eating only meats that are fully cooked, wearing a mask in public if indicated,

For thrombocytopenia: Avoiding activities where you could be injured (such as contact sports), being careful or eliminating shaving, using a soft toothbrush, don't take anti-inflammatory medications (such as Advil) that can increase bleeding. Keep in mind that some over-the-counter medications (such as aspirin) and nutritional supplements (such as ) may increase bleeding time as well.

A Word From Verywell

There are many causes of myelosuppression, and determining the cause is important in figuring out the best treatment options. Work with your healthcare provider to understand your diagnosis and determine the best treatment options for you as an individual. And remember that there are things you can do yourself that may reduce any symptoms you experience due to myelosuppression.