Myelodysplasia in Cats-Causes, Symptoms & Treatment


What is myelodysplasia?  Causes   Symptoms  Diagnosis   Treatment   Prognosis

At a glance

About: Myelodysplasia is a group of diseases caused by a dysfunction of blood cell production in the bone marrow. It can affect red or white blood cells and platelets.

Causes: FIV and FeLV, exposure to toxins such as lead, chemotherapy, copper deficiency and myeloid leukemia. In most cases, it will not be possible to determine the cause.

Symptoms: There can be a variety of symptoms depending on the cells affected.

  • Anemia: pale gums, lethargy, rapid breathing and heart rate.
  • Leukopenia: Mouth ulcers, recurrent infections, fever and fatigue.
  • Thrombocytopenia: increased bleeding, black tarry stools.

Diagnosis: Complete physical examination, accompanying symptoms and history. A bone marrow biopsy under general anesthetic can confirm the diagnosis.

Treatment: Blood transfusions, antibiotics (where needed), hematopoietic growth factors, immunosuppressive drugs, low dose chemotherapy. The only cure for myelodysplasia is a bone marrow transplant (rare).

Myelodysplasia in cats


Myelodysplasia syndrome (MDS) is a group of blood diseases arising from dysfunction from the hematopoietic stem cells which start to produce abnormal immature myeloid cells.  

The disease causes cytopenias (cytopenia is the medical term for a reduction in any of the three types of blood cells) in the peripheral blood and dysplastic changes in the bone marrow cells.

For cats with myelodysplasia, the myeloid cells start to produce abnormal immature blasts, which are unable to mature and develop as normal blood cells should, or, if specialised blood cells are made, they die shortly before or after leaving the bone marrow.

The myeloid cells produce three types of blood cell:

  • Red blood cells (erythrocytes) – These cells transport oxygen around the body. Anemia is a reduced number of red blood cells.

  • White blood cells (leukocytes) – Responsible for fighting infection. Leukopenia is a reduced number of white blood cells.

  • Platelets (thrombocytes) – Not cells but cell fragments, platelets are a part of the blood clotting process, forming a plug to stop bleeding. Thrombocytopenia is a reduced number of platelets.

 blood cell formation in the bone marrow of cats

Myelo=marrow (myeloid cells), dys=abnormal, plasia=appearance.


Below is a very basic description of the development of blood cells, which is known as hematopoiesis.

Normal blood cell production

Normal blood cell production in cats

Multipotential hematopoietic stem cell (hemocytoblast) > Immature myeloid cells > Immature specialised cells (red, white, megakaryocyte, the latter will form platelets)  Specialised cells mature (red, white or platelets) which are released into the bloodstream.

Myelodysplasia (abnormal) cell production

Hematopoietic stem cell > Abnormal immature myeloid cells can crowd out normal stem cells as they are often no longer able to move onto the next step and differentiate into red, white blood cells and platelets, or they do become immature specialised cells but are abnormal > Specialised cells (red, white cells or platelets) aren’t produced, or are produced but are abnormal and die shortly before or after being released into the bloodstream

Usually, the percentage of myeloid cells in the bone marrow is between 2-3%, cats with myelodysplasia often (but not always) have a much higher number of abnormal immature myeloid cells. Once that number goes over 20%, the disease has progressed to acute myeloid leukemia (AML). That is why myelodysplasia is sometimes referred to as preleukemia.

Myelodysplasia can involve one cell line, for example, red blood cell only, or multiple cell lines. Erythrocytes (red blood cells) are the most common cell involved.

Refractory cytopenia with unilineage dysplasia (RCUD) means that your cat has low numbers of one type of blood cell. For example:

  1. Refractory thrombocytopenia means he has low blood platelets but normal red and white blood cells.
  2. Refractory anemia means he has low red blood cells but normal white blood cells and platelets.
  3. Refractory leukopenia means he has low white blood cells but normal red blood cells and platelets.

Refractory cytopenia with multilineage dysplasia (RCMD) means that more than one type of blood cell is affected.

There are no age or gender predilections with this myelodysplasia, Persians, and Birmans appear to be slightly over-represented. Cats with feline immunodeficiency disease and feline leukemia are at higher risk of developing myelodysplasia. It may be primary or secondary.

  • Primary myelodysplasia arises from mutations in the stem cells.

  • Secondary myelodysplasia is due to myeloid leukemia, copper deficiency, exposure to toxins such as lead, nutritional deficiency or certain drugs such as chemotherapy or radiotherapy and the feline leukemia virus.


Symptoms depend on the affected cell line(s), but may include:

Anemia (red blood cells)

Leukopenia (white blood cells)

Thrombocytopenia (platelets)

  • Increased bleeding such as nosebleed or gums
  • Black tarry stools due to internal bleeding

Other symptoms

If more than one cell line is affected, your cat will experience a combination of the above symptoms.


Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you including any drug therapies your cat has received.

Diagnostic workup:

Baseline tests such as biochemical profile, complete blood count, and urinalysis. These can help to show how your cat’s organs are functioning if an infection is present and give a count of the types of blood cells, which will reveal anemia, leukopenia, thrombocytopenia or a combination. There may also be abnormally formed cells in the blood. These will give your veterinarian a preliminary diagnosis.

As there are many causes of anemia, leukopenia, and thrombocytopenia, he will need to perform some additional tests to narrow down the cause.

Bone marrow biopsy: Your cat will be anesthetised, and a needle will be inserted into the bone of the pelvis or the femur and into the centre where the bone marrow is. The sample will go to a laboratory for evaluation. The normal percentage of myeloid cells within the bone marrow is around 2-3%, a cat with myelodysplasia may have a much higher percentage of myeloid cells although it is possible for the myeloid cell numbers to be normal or even reduced.

Blood smears: To examine the morphology (shape and structure) of the circulating blood cells.

Your veterinarian may also recommend a FeLV and FIV test as a large number of cats with myelodysplasia are infected with these viruses.


Treatment depends on the type of myelodysplasia and the severity of the condition.

  • Whole blood or platelet transfusions to maintain blood cell and platelet counts. Platelets don’t live for long so transfusions of platelets will need to be more frequent than whole blood. Cats who receive whole blood are at increased risk of iron overload.

  • Broad-spectrum antibiotics where needed.

  • Hematopoietic growth factors are proteins which can stimulate cell differentiation and production. Erythropoietin (EPO), granulocyte colony-stimulating factor (G-CSF) and granulocyte-monocyte colony stimulating factor (GM-CSF).

  • Immunosuppressive drugs can be prescribed if it is the cat’s immune system slows down the production of blood cells.

  • Low dose chemotherapy administered orally, or via injection. These drugs can help the cells of the bone marrow develop normally by killing rapidly dividing (abnormal) cells, and help prevent the disease from progressing to acute myeloid leukemia (AML).

There only cure for myelodysplasia is a bone marrow transplant. This is used in some human cases; usually when the patient is young; however, it is only experimental in cats. The procedure involves high doses of chemotherapy to destroy the patient’s own dysfunctional bone marrow cells, followed by a bone marrow transplant from a healthy cat. The procedure is highly intensive and not without risks.

Possible outcomes

There are three possible outcomes in cats who have myelodysplasia; the cat will go on to develop acute myeloid leukemia, live with a chronic disease or die.


  1. Hello,
    This was a wonderful article, very well laid out, easy to understand… which is great when you are in shock over receiving this diagnosis for your cat.
    The reason I”m writing is that I would like to know what the conclusion was supposed to be…. at the very end, only two words “The procedure” are there.. What was the rest of the thought? If bone marrow transplant is feasible, I would do it for her.

    Thank you.

    • Hmmm, you’re right. I’m not sure what happened to that. I will edit it tomorrow (Monday). Has your cat been diagnosed with myelodysplasia? For me personally, I wouldn’t go ahead with a BMT, but a friend’s son had myelodysplasia (affected his platelets), and undergo a BMT and while he had a 75% chance of survival, the BMT failed and he sadly did not make it. I’m not sure I could do that to a cat.

  2. Hi Julia,
    Thank you for filling in the missing part of the article.
    Yes and no on the diagnosis – my kitty did have the BMB and came through it very well, only needed pain meds for a couple days and she really didn’t seem to have any after effects. MDS is very likely, although leukemia is as well. The slides are being reviewed at CSU and I’ll have results in a week or so. Either way, outlook is not wonderful as she is transfusion dependent, currently, For now, that is what we will do until the results come in. For my cat, it is her red cells that are most affected. If it is cancer, will consult with oncologist and go from there… Right now QOL is still good, ( with blood) which is first and foremost – if that changes, so will the plan to the best thing for her 🙁

    Thanks again.

    • Hi Christy, thanks for getting back to me. I’m always curious to know how cats go after medical procedures. Have you had any results back yet? Please let me know how you go and what treatment options you decide. I hope it’s a positive result, it’s so stressful waiting on results 🙁

  3. Hi,
    My kitty was diagnosed a few weeks ago and she has good days and bad days. I was just wondering what to expect in the future. I notice her back legs are losing some function (could be that she lost so much weight?), but not every day, one of her ears is starting to droop a little. She still eats, purrs, cries to go outside (which she does not) and cuddles. Is this normal? Is there more changes coming? Does anyone know?


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