Medullary Aplasia in Dogs - Symptoms and Treatment

Medullary aplasia in dogs is a complex disease that affects the production of blood cells. Learn about it here in a language that everyone can understand.
Medullary Aplasia in Dogs - Symptoms and Treatment

Last update: 29 March, 2022

The term aplasia comes from the Greek and refers to the defective or non-existent formation of cells. In this article, we’re going to talk about a specific field, hematology, and the disease known technically as medullary aplasia in dogs.

It’s a rare disease in dogs and its origin is often unclear. In addition, this medical condition varies depending on the blood cells that are affected. If you’re interested in learning more about medullary aplasia, here’s all the basic information about the condition explained in simple language. Keep reading!

What is medullary aplasia?

In medullary aplasia, there’s a deficit or absence of formation of precursor cells of the erythroid, myeloid, and megakaryocytic lines. These precursor cell bodies are stem cells from which red blood cells, different types of white blood cells, and platelets are created.

The entire marrow isn’t always affected in this condition (which would be called total aplasia), but sometimes a partial aplasia scenario is found. As the marrow deteriorates, the excess space is replaced by poorly functioning adipose (fatty) tissue.

Red blood cells are essential for oxygen transport, white blood cells maintain immune function, and platelets enable clotting. Deficiencies can be lethal.

A pug with a vet.

Causes of spinal cord aplasia

Although it’s often impossible to determine the cause of aplasia, there are certain factors that can trigger it. The most important of these are as follows:

  1. Drugs: A dog can develop bone marrow aplasia if exposed to chemotherapy, estrogens, cephalosporins, azathioprine, trimethoprim/sulfadiazine, azathioprine, or phenylbutazone. Discuss with a veterinarian the possible side effects of any medication you’re giving your dog and follow the directions.
  2. Environmental toxins: Varnish, paint, insecticide, and other household chemicals are just a few examples of toxic agents that promote this condition.
  3. Microorganisms: The bacterium Ehrlichia canis (the cause of ehrlichiosis), transmitted by tick bites, can cause medullary aplasia. The same applies to canine parvovirus.
  4. Hematopoietic neoplasia: This term refers to abnormal growths in hematopoietic cells (the aforementioned precursors of blood cells). They’re considered to be cancerous, although they don’t manifest as tumors.
  5. Chronic renal failure: The kidneys produce a hormone, erythropoietin, which stimulates the production of red blood cells. When this hormone isn’t released due to the degeneration of kidney tissue, fewer red blood cells than necessary are created and this will cause anemia.

Symptoms of medullary aplasia in dogs

Depending on what percentage of marrow is affected, the symptoms of this disease will vary between the typical clinical signs of anemia, leukopenia or thrombocytopenia. These are listed in detail below:

  • Symptoms of anemia: These occur when the main deficit is in red blood cells. You can observe pale mucous membranes, weakness and intolerance to exercise, agitated breathing, and increased heart rate in the affected dog. Some of these signs derive from the lack of oxygen in various body tissues.
  • Symptoms of leukopenia: These appear in the absence or deficit of white blood cells, so the dog will be much more prone to develop secondary infections. It’ll also be more prone to suffer bacteremia (when bacteria enters the blood).
  • Symptoms of thrombocytopenia: In this case, the platelets aren’t produced in sufficient quantities, and so you’ll notice that your dog’s wounds don’t heal in the normal time. It’s also possible that minor hemorrhages, such as nosebleeds, or more serious hemorrhages, such as bleeding of the organs, may occur.

How to diagnose the disease

There are two main tests to confirm a suspicion of medullary aplasia in dogs: a blood test and a biopsy. The vet will also need to check if the dog has acute leukemia.

With the blood test, the vet will be wanting to find out how many erythrocytes, leukocytes, and platelets there are and in what proportion they occur in the dog’s plasma. Once the reduction in the number of blood cells is confirmed, a bone marrow sample will be taken.

This sample can be taken by aspiration or by means of a biopsy. The former is useful to assess the morphology of the cells (which is altered when they try to compensate for the low number of cells remaining in the blood). The biopsy, on the other hand, shows the structure of the bone marrow itself and makes it possible to observe what proportion of adipose tissue has been created recently.

Biopsy is the best technique when very few blood cells are seen in the blood test.


Treatment for this disease varies depending on which cell line is affected. However, it’s rare for only one cell line to be diminished, and so the approach usually covers the entire spectrum of symptoms. Veterinarians will consider the following options depending on the level of severity of the pet:

  • Antibiotics: These are prescribed to prevent infections or to fight infections already present due to a lack of white blood cells. Open wounds must be disinfected thoroughly and often, in order to prevent this.
  • Stem cell injection: These cell bodies modulate the creation of defenses, are anti-inflammatory, and help to repopulate the bone marrow. To avoid rejection, antilymphocytic or antithymocytic globulin is administered to the dog as a complement.
  • Hematopoietic growth factors: These are hormone-like substances that stimulate the bone marrow to produce blood cells.
  • Immunoglobulins or antibodies: The injection of specific antibodies can make it easier for the dog’s body to fight off some viruses and bacteria.
  • Corticosteroids: These regulate the immune system and reduce the intensity of inflammatory processes.
  • Bone marrow transplantation: This is recommended for young dogs with severe medullary aplasia. Cyclosporin A is administered to prevent transplant rejection.
A vet with a dog.

Medullary aplasia has a medium to severe diagnosis, as the response to treatment is usually poor. A good diagnosis which detects what’s causing the disease (if possible) will be key to give some hope that the dog will recover well. Don’t hesitate to go to your trusted vet clinic when you notice any of the signs of illness that we’ve mentioned in this article.

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