Bone Marrow Aplasia in Dogs

Hypoplasia refers to the underdevelopment of an organ or tissues. When this occurs in the bone marrow, it prevents the creation of sufficient erythroid, myeloid and megakaryocytic cells. These are the cells which create blood cells, platelets and other vital components of the dog's organism. Most significantly, it affects the ability to create red blood cells (erythrocytes), white blood cells (leukocytes) or platelets in the peripheral blood.

Since the creation of blood cells is affected, it is also known as aplastic anemia. Blood marrow aplasia is total if all the precursors are affected and is known as total pancytopenia. It is possible the failure is partial if only some of them are. The absence of hematopoietic tissue is replaced by adipose tissue, which occupies up to 95%.

Causes of bone marrow aplasia in dogs

Bone marrow aplasia or aplastic anemia in dogs can occur due to the following causes:

• Drugs: exposure to chemotherapeutics, azathioprine, trimethoprim/sulfadiazine, exogenous or endogenous estrogens, phenylbutazone, cephalosporins, phenothiazine, captopril or chloramphenicol.
• Environmental toxins: insecticide, benzol, varnish or paint.
• Microorganisms: Ehrlichia canis (Ehrlichiosis ) which infects progenitor and proliferative cells in the bone marrow.
• Hematopoietic neoplasia: abnormal growths in the hematopoietic cells of the bone marrow.
• Chronic kidney failure: has various causes and symptoms.

In addition, a congenital red cell aplasia called Diamond-Blackfan anemia has been described in dogs, specifically affecting young dogs. It causes an absence of erythroid precursors, but the others are intact. An idiopathic or primary aplasia, apparently of immune-mediated origin, is also known, since it responds to corticosteroid therapy.

The clinical picture of canine aplastic anemia will vary according to the degree to which cells in the bone marrow are affected. Total pancytopenia is most serious, since it will cause symptoms related to the lack of red, white and platelet cells: There are various consequences on the affected dog and is lethal in some cases.

The symptoms associated with an erythrocytic aplastic anemia (that which causes a lack of red blood cells) are those similar to other forms of anemia. They include:

• Pale mucous membranes
• Tachycardia (rapid heart rate)
• Tachypnea (rapid breathing)
• Fatigue
• Debilitation
• Exercise intolerance
• Palpitations

When white blood cells are missing, a lack of immune cells responsible for the immune response of the dog causes the dog to have lower immunity. This makes the dog susceptible to all kinds of infections. This can cause osteomyelitis in dogs if the bone itself is infected.

If platelets are missing, dogs will have a tendency to bleed profusely since platelets are involved in blood clotting. These hemorrhages can be minor, such as oral or nasal bleeding. In the worst case scenario, they will occur in internal organs, such as the digestive system or the brain, putting the dog's life at risk.

The diagnosis of medullary aplasia is achieved with a blood test. This canine blood test will be to assess the number of red, white and platelet cells, which are decreased in this disease. Acute canine leukemias should be included in the differential diagnosis.

Once the reduction of bone marrow ability is confirmed, a bone marrow sample should be taken by aspiration or biopsy:

• Aspiration samples allow individual cell shape to be assessed and the myeloid-erythroid ratio determined.
• The biopsy indicates the structure of the marrow and its global cellularity. It is the technique of choice in cases of hypocellular marrow or that has been replaced by fatty tissue. In this sample the absence of hematopoietic cells will be observed.

Bone marrow sampling

Bone marrow samples are taken from dogs at the following locations:

• Proximal epiphyses of the humerus and femur
• Iliac crest
• Wing of the ilium
• Ribs
• Breastbone

Both aspiration and biopsies can be very uncomfortable for the dog. They are often performed under general anaesthetic.

The treatment of medullary aplasia in dogs will depend on the types of cells affected. In general, we can see the following treatment options:

• Antibiotics and asepsis: in cases of leukocyte aplasia to prevent infectious diseases.
• Stem cell therapy: for their immunomodulatory and anti-inflammatory activity. They are responsible for repopulating the bone marrow by their ability to differentiate into blood cells.
• Hematopoietic growth factors: given as part of chemotherapy.
• Immunoglobulin therapy: may only provided temporary relief from bone marrow aplasia.
• Anti-lymphocytic or antifungal globulin therapy: can eliminate certain fungal-related aspects of the disease.
• Cyclosporin A: used as an immunosuppressant if the immune response is affected.
• Corticosteroids: steroid hormones.
• Bone marrow transplant: is only likely for young dogs with severe aplastic anemia and only if the resources are available.

Prognosis of bone marrow aplasia in dogs

Canine medullary aplasia generally has a poor prognosis. It is a pathology in which, in many cases, the response to treatment is poor. Consequently, it can lead to the death of our dog, especially if it does not respond to immunosuppression or the origin of the spinal aplasia is not detected. Fortunately, it is also relative uncommon. It will need to be diagnosed by a qualified veterinarian, one of the reasons it is so important we have regular veterinary checkups for our dog.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

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