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Understanding Aplastic Anemia in Dogs

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Aplastic Anemia in Dogs

Aplastic anemia in dogs is a condition that is not very common, but when it occurs, it can potentially lead to devastating consequences. This type of anemia often tends to occur as an adverse reaction to certain drugs and chemicals which produce toxic effects on the dog's bone marrow. When the bone marrow is negatively affected, its job in creating important blood cells is disrupted which leads to a cascading chain of events which result in illness in affected dogs. If you suspect your dog is suffering from aplastic anemia, it's important to see the vet as soon as possible for proper diagnosis and treatment.

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A Matter of Low Blood Cells

Aplastic anemia, also referred to as aplastic pancytopenia, is a condition in which the dog's bone marrow stops the normal production of blood cells. How does this happen? In order to understand the process, one must take a closer look at how the bone marrow works.

The bone marrow is responsible for making all types of blood cells found in the body. Among these cells, are the red blood cells, which are responsible for delivering oxygen to all tissues of the body, the white blood cells, which combat infections, and the platelets, which are responsible for allowing the dog's blood to clot preventing hemorrhage. When these cells are fully mature they are released into the dog's bloodstream so they can do their jobs.

When aplastic anemia takes place though, the structure of the bone marrow is disrupted which causes it to reduce the production of all the above described blood cells (known as hematopoietic cells) while replacing them with large amounts of fat. The condition of having a reduction in the production of all three types of blood cells is medically known as pancytopenia.

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What causes this condition often remains unclear, and therefore it's often medically referred to "idiopathic aplastic anemia." In the acquired form though the disease is triggered by exposure to certain drugs and toxins or infection (parvo, ehrlichia) with certain viruses or other disorders. In certain cases, the condition is caused by the immune system (autoimmune).

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Drugs Causing Aplastic Anemia

While the drugs in this list are meant to heal or make dogs feel better, at times, things may not go as planned. It can be that toxic effects occur as a result of an exaggeration of the drug's pharmacological effects or there may be other predisposing factors at play.

This list of drugs is therefore not to label these drugs as "bad," but just to raise awareness of any potential early warning signs of potential complications. Generally, vets suggest use of these drugs as their benefits outweigh the risks. There are several types of drugs that have been reported to potentially cause aplastic anemia. Following is a brief list.

Several anticancer drugs and chemotherapy drugs such as busulfan, cyclophosphamide, cytosine arabinoside, methotrexate, mustargen, vinblastine and vincristine are a few examples. Radiation has also been reported as a potential cause.

Among antibiotics, fingers have been pointed towards amphotericin B, chloramphenicol, methillicin, quinacrine, sulfonasmides and tetracyclines.

Other drugs reported include endocrine agents (estrogens, thiouracil, thiocynate and tolbutamide), tranquilizers (meprobramate, phenotiazines), antihistamines (chlorpheniramine and tripelennamine), antiparasitic drugs (albendazole), and certain NSAID drugs prescribed for pain and inflammation. There may be several other drugs reported to cause aplastic anemia in dogs that are not listed.

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Signs of Trouble

As one may image, lowered numbers or red blood cells (anemia), lowered numbers of white blood cells (leukopenia) and lowered numbers of platelets (thrombocytopenia) can certainly take a toll on the affected dog, causing a variety of debilitating symptoms.

Dogs affected by aplastic anemia tend to develop symptoms that are similar to those of other forms of anemia. Because there are lower levels of red blood cells and therefore less oxygenated blood circulating, affected dogs will become weak and lethargic, and an increased heart rate may be present as well as a defensive mechanism.

Because there is reduced number of platelets, dogs may develop pinpoint hemorrhages in the skin (petechiae), bruising (ecchymosis) and bleeding from the gums, nose and intestine. Some dogs also develop blood in their urine and feces.

Also, since there are reduced numbers of white blood cells around to fight infections, dogs affected by aplastic anemia may be also become more vulnerable to infections.

Signs of aplastic anemia may arise acutely leading to rapid progression or the disorder may have a more insidious chronic onset as the body is gradually depleted from blood cells.

 At the Vet's Office

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Your vet will ask several questions about your dog, the symptoms you have been seeing and whether your dog has taken any drugs or toxins known for causing aplastic anemia.

On physical examination, your vet may look at your dog's gums and look for any physical signs suggesting anemia. The vet will listen to the heart, take a temperature and respiratory rate.

Blood work will be conducted so to look at the numbers of cells. Red blood cells, white blood cells and platelets are typically produced in lower numbers in dogs suffering from aplastic anemia.
The most definite diagnosis is obtained by bone marrow biopsy, a procedure where a small sample of bone marrow is obtain via aspiration or biopsy. The sample is then analyzed under microscope. Sedation or anesthesia is required for this procedure.

Treatment for aplastic anemia in dogs varies depending on the underlying cause. If the vet suspects an autoimmune disorder, he/she will prescribe steroids(cyclosporine A, prednisolone). Antibiotics may be given to treat any underlying infections or prevent them from occurring. If the vet suspects that a drug may be the culprit he will suggest discontinuing its use. Blood transfusions may be needed.

Supportive care must often be given to ensure proper nutrition. Veterinarians may recommend hospitalization.Without treatment, aplastic anemia may progress to death, hence the importance of swift diagnosis and treatment.

References:

  • Iowa State University, Digital Repository, A Case Report of Aplastic Anemia in a Dog Steven I. Raiser Iowa State University Johnny D. Hoskins Iowa State University
  • Textbook of Veterinary Internal Medicine, by Stephen J. Ettinger DVM DACVIM (Author), Edward C. Feldman DVM DACVIM (Author), Etienne Cote DVM DACVIM(Cardiology and Small Animal Internal Medicine) (Author) Saunders; 8 edition (January 2, 2017)

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