Overview of Canine Immune Mediated Hemolytic Anemia in Dogs (IMHA)
Immune mediated hemolytic anemia (IMHA), also known as auto-immune mediated hemolytic anemia (AIHA, is a disease in which the body’s immune system, which is designed to attack and kill germs, attacks and kills the body’s own red blood cells. The attack begins when antibodies, which are molecules made by the immune system to target germs, instead attach to and target the animal’s own red blood cells for destruction. The red blood cells carry oxygen to the tissues, and the animal cannot survive without adequate oxygenation of the tissues.
IMHA may also be known as pure red cell aplasia (PRCA) or Evans syndrome (if it coexists with immune-mediated thrombocytopenia).
The causes of IMHA remain largely unknown. While some cases of IMHA may be associated with a triggering event (cancer, infection, and perhaps even vaccinations), these events do not explain why the immune system misdirects its arsenal of weapons against the animal it is meant to protect.
IMHA occurs more often in dogs than in cats, in middle-aged animals (3 to 8 years old), and in more females rather than males. While any breed can be affected, certain breeds develop IMHA more often than others do, such as the cocker spaniel, English Springer spaniel, miniature poodle, miniature schnauzer, Doberman pinscher, Finnish Spitz, Irish setter, Dachshund, bichon frise, collie, and Old English sheepdog.
For unknown reasons, there is an increased incidence of disease in the spring, with 40% of cases diagnosed in the months of May and June.
IMHA is a rapidly life-threatening disease. Even with appropriate treatment, this disease can be fatal.
What To Watch For
Signs of Immune Mediated Hemolytic Anemia (IMHA) in dogs may include:
- Pale gums
- Yellow tinged gums or whites of the eyes
- Discolored urine e.g. dark or dark yellow
- Tiring easily
- Progressive weakness
- Loss of appetite
- Tachypnea (rapid breathing)
Diagnosis of Immune Mediated Hemolytic Anemia in Dogs
Your veterinarian will recommend the following tests:
- A complete history and medical examination. Be prepared for questions about any medications your animal may have received, when the most recent vaccinations were given, and questions about the color of urine and stool.
- Complete blood count (CBC) should be performed on all dogs suspected of having anemia (decreased number of red blood cells), regardless of the cause.
- A “packed cell volume,” or PCV, is a quick and simple test for the number of red blood cells present.
- Reticulocyte counts allow the veterinarian to determine if new red cells are being made in appropriate quantities.
- A serum biochemical profile and urinalysis may be performed to give clues as to possible causes of the anemia.
- A saline agglutination test is a simple blood test that may show if the red cells are clumping together.
- A Coombs test is often indicated. A sample of your dog’s blood is incubated with special reagents to look for evidence of an immune reaction to the blood.
- Radiographs, ultrasound examinations, or blood tests for infectious diseases may be indicated in some patients. These examinations may help rule out causes of anemia other than IMHA, or may help identify triggers that preceded development of IMHA.
Treatment of Immune Mediated Hemolytic Anemia in Dogs
- Corticosteroids (such as prednisone, prednisolone, or dexamethasone) are the mainstays of treatment for IMHA. They suppress the immune system’s attack on the red cells.
- In the most severe cases, or those cases that fail to respond to corticosteroids, other immunosuppressive agents may be utilized. These include drugs such as azathioprine, cyclophosphamide, cyclosporine, danazol, or leflunomide.
- Intravenous immunoglobulins, a product made from human blood, has been used with some success in a few cases of IMHA.
- Plasmapheresis, or the process of removing antibodies from the blood, is very rarely available to veterinarians, but may be possible in some special hospitals.
- Because the spleen is responsible for removing many of the antibody targeted red cells, splenectomy (removal of the spleen) may benefit some animals after initial treatment and stabilization.
- Supportive care is essential to the successful treatment of IMHA. Such care may include transfusion, nursing, and medications.
- Transfusion of either whole blood (cells plus the liquid plasma) or of packed red blood cells (cells only after the liquid is removed) may prove life saving.
- Administration of a blood substitute (Oxyglobin®) provides the ability to carry oxygen to the tissues without administering blood itself.
- Complications of IMHA include the formation of blood clots. Heparin is a medication that helps prevent formation of these clots.
- Intravenous fluids may be indicated to prevent dehydration in some dogs.
Home Care and Prevention
It is crucial to administer all prescribed medications as directed. Even a few missed doses can have serious consequences.
Allow the dog to limit his activity. Anemic animals should not be encouraged or expected to engage in active play.
Provide adequate nutrition. Encourage the dog to eat a well-balanced dog food, but your veterinarian can suggest appropriate enticing treats for the animal that refuses food.