Anemia Due to Bone Marrow Failure (or Toxicity) in Dogs

Aplastic Anemia in Dogs

Bone marrow plays a pivotal role in the origination and constant replenishment of important cells like red blood cells (RBCs), granulocytes (or white blood cells [WBCs]), and platelets. Once these cells reach the point of maturation they are released from the marrow into the blood stream. In some mammals, it is estimated that as many as three million red blood cells per second are released into the blood circulation, demonstrating the extensive amount of work done by the bone marrow in keeping the numbers of these cells within normal ranges in the body.

Aplastic anemia in dogs is a diseased condition resulting from the bone marrow's inability to replenish blood cells. Where aplastic refers to the dysfunction of an organ, and anemia refers to a lack of red blood cells. Aplastic anemia is a life-threatening condition resulting when normal bone marrow is replaced by adipose (fat) tissue, thus preventing it from releasing the required number of WBCs, RBCs, and platelets and resulting in an overall decrease in the total number of these cells in the blood. RBCs have several vital functions in the body, including carriage of oxygen and removal of waste carbon dioxide. WBCs are essential for fighting infections and foreign particles, whereas platelets are required for clotting the blood and preventing hemorrhage. All symptoms seen in aplastic anemia directly relate to the functions of these cells. In most cases of aplastic anemia, all three types of cells are affected. If left untreated, this condition can lead to death in severely affected dogs.

Symptoms and Types

All three types of cells affected in this disease have different roles to play in normal body functions, therefore, the symptoms will vary depending on the type of cells mostly affected and the severity of the problem. Following are some of the symptoms related to aplastic anemia.

• Recurrent infections
• Fever
• Petechial hemorrhage (red or purple spots on skin due to tiny hemorrhages)
• Blood in urine (hematuria)
• Nosebleed (epistaxis)
• Black-colored feces (melena)
• Pale mucous membrane
• Weakness
• Lethargy

Causes

There are a variety of causes for aplastic anemia, including infections, toxins, drugs, and chemicals which may cause aplastic anemia in dogs. Following are some major causes of aplastic anemia in dogs:

Infections

• Canine parvovirus infection
• Rikettsial organism infections (e.g., ehrlichia)

Drugs and chemicals

• Estrogen administration
• Chemotherapeutic drug administration
• Albendazole (for parasitic treatment)
• Some types of antibiotics
• NSAIDs (given for relief of pain and inflammation)
• Radiation therapy in cancer patients

Diagnosis

You will need to give a thorough history of your dog's health and onset of symptoms. Your veterinarian will perform a physical examination with full laboratory testing, including complete blood tests, biochemical profiles, and urinalysis. The results of these tests will provide valuable information for the preliminary diagnosis. The count of various cells will be determined; counts that are far below the normal ranges are considered a positive result.

Your veterinarian will also evaluate your dog for the presence of any infectious diseases, but the most valuable test in the diagnosis of aplastic anemia is bone marrow sampling. In this test a small sample of bone marrow will be collected through aspiration or biopsy. The microscopic studies will reveal the important information related to the architecture of the bone marrow and any developmental problems of the various cells in the bone marrow.

Treatment

Your veterinarian will start treating your dog immediately after a confirmatory diagnosis has been made. Your dog may need to be hospitalized for few days to be monitored and treated. With aplastic anemia, there are number of problems to deal with and supportive therapy will be initiated to provide the required nutrition and energy that your dog is lacking. If required, whole blood transfusions may be recommended for severely anemic patients. As this problem is mediated mostly through the immune system, the primary treatment involves suppressing the immune system with drugs like cyclosporine A. Cyclosporine and other related agents suppress the bone marrow’s over-response. Drugs supporting the bone marrow functions are also recommended for these patients. Antibiotics are given to treat ongoing infections as well as for the prevention of further infections.

Living and Management

During hospitalization, your veterinarian will monitor your dog's status daily. Blood tests will be repeated to determine the current status of the problem. In some dogs, bone marrow sampling may need to be repeated in order to see if the bone marrow is responding normally or not. Unfortunately, with aplastic anemia few patients survive despite extensive care and treatment. Young dogs have a better chance of survival, but even if initial recovery is attained, it may take several weeks to months for a complete recovery.

---