immune mediated hemolytic anemia in dogs

Immune Mediated Hemolytic Anemia in Dogs (IMHA), Autoimmune Hemolytic Anemia

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:

Diagnosis of Immune Mediated Hemolytic Anemia in Dogs

Your veterinarian will recommend the following tests:

Treatment of Immune Mediated Hemolytic Anemia in 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.

Because we do not understand what causes IMHA, there are no known preventive measures. If an animal’s gums are noted to be pale or white, and the animal appears weak, seek emergency veterinary assistance.

In-depth Information on Immune Mediated Hemolytic Anemia in Dogs (IMHA)

Immune mediated hemolytic anemia is exactly what the name implies. “Anemia” is a deficiency of red blood cells, and may result from many causes including bleeding, failure to produce enough new red blood cells, or destruction of existing red blood cells. “Hemolysis” refers to the lysis, or destruction, of the red blood cells (“heme” is an essential component of red blood cells that allows them to carry oxygen). The term “immune mediated” simply states that in these cases the process of red blood cell destruction is carried out by the immune system.

The immune system is a complicated network of cells and products that are secreted from cells. In a healthy animal, these cells and their products recognize germs as being foreign, and they attack and destroy those germs. The immune system is designed to recognize the animal’s own cells as being harmless, and to refrain from attacking the animal’s own healthy cells. When an animal develops immune mediated disease, the immune system destroys the animals own cells rather than just germs. Sometimes the attack on the animal’s own cells is accidental, and sometimes it is purposeful. A purposeful attack is said to be an “autoimmune” process. In those cases, the immune system thinks the animal’s own cells are foreign, and attempts to destroy them. This destructive process may be directed against many different cell types, but when the cell type under attack is the red blood cell, immune mediated hemolytic anemia is the result.

The development of immune mediated disease is complicated and poorly understood. In some cases a trigger can be identified that may have precipitated the misdirection of the immune system, but in most cases, such a trigger is never found. IMHA, like most such diseases, occurs more often in females than in males. Young adult to middle aged animals are most likely to be affected, and dogs develop the disease much more frequently than do cats. While any dog may develop IMHA, cocker spaniel, Springer spaniel, miniature poodle, Finnish spitz, Irish setter, bichon frise and Old English sheepdog are more likely than most to be affected.

Immune mediated hemolytic anemia is a rapidly life-threatening disease. With severe anemia of any cause, the tissues are unable to receive adequate oxygen. In cases of IMHA, destruction of red cells results in a sudden, and often very severe, decrease in red blood cell numbers. Although there is usually a substantial increase in the number of new red blood cells produced within the bone marrow, production of new cells cannot keep up with the rapid destruction of cells. Unless the immune system’s attack on the red cells can be curbed, the animal will die. Swift treatment may stop the attack, allowing the newly made red blood cells to replace those that were destroyed. Unfortunately, it is not always a simple matter to stop the immune attack, and there are many potential complications of IMHA. Although many animals treated for IMHA go on to live full lives, even those who receive appropriate therapy may succumb to the disease.

There are different forms or subtypes of IMHA. They are most commonly referred to as primary, secondary, intravascular and extravacular.

Differential Diagnoses (Other Causes of Anemia) in Dogs

It is crucial that the diagnosis of IMHA be confirmed, because there are many causes of anemia other than IMHA. Both treatment and prognosis for these other causes are often quite different that that of IMHA. Other potential cause of anemia include:

In-depth Information on the Diagnosis of Canine Immune Mediated Hemolytic Anemia in Dogs (IMHA)

Expect your veterinarian to obtain a complete medical history. Be prepared for questions about what symptoms you have observed and how long they have been present, any medications your animal may have received, when the most recent vaccinations were given, and questions about the color of urine and stool.

In-depth Information on the Treatment of Canine Immune Mediated Hemolytic Anemia

Treatment of IMHA involves both direct attempts to halt the immune system attack on the red blood cells, and supportive care. The immune system is a complicated network of cells and cell products all designed to protect the body from foreign invaders. As with any complicated system, there are multiple places where errors can occur. When these errors result in the destruction of red blood cells (that is, IMHA), the immune system’s attack must be halted if the animal is to survive. Unfortunately, the drugs available to halt the attack are not specific, meaning that they not only diminish the attack on the red blood cells, but also interfere with appropriate immune response to germs. This puts the animal undergoing therapy for IMHA in the precarious position of needing just enough, but not too much, immune suppression.

The drugs available to suppress the immune system interfere with entire pathways of immunity, and occasionally more than one of these paths must be interrupted to stop destruction of the red blood cells. In most dogs that respond successfully to therapy, the dose of immunosuppressive drugs can be very gradually lowered. Some animals will eventually be able to discontinue medications altogether, while others will require life-long therapy. Almost all immunosuppressive therapies require some time to take effect. Until the destruction of red cells can be halted, supportive care is crucial for the animal’s survival.

Immunosuppressive Therapy

Corticosteroids (such as prednisone, prednisolone, or Dexamethasone) suppress the immune system’s attack on the red cells by several mechanisms and are the mainstays of treatment for IMHA. While the effect of corticosteroids is more rapid than that of many other immunosuppressive drugs, it is still often 3 to 4 days before a positive response may be seen. Initial dosages of corticosteroids are very high, and may be associated with unpleasant side effects such as increased thirst and appetite, along with increased urination and weight gain. The dosage will be slowly decreased over several months after the animal improves.

Adjunctive Immunosuppressive Drugs

Supportive Care

Supportive care is essential to the successful treatment of IMHA. Such care may include transfusion, nursing, and medications. Additional supportive therapies include:

Prognosis of Dogs with IMHA

The prognosis depends on the dog’s response to treatment and the diagnosis and treatment of any possible underlying cause for the disease. The prognosis is generally considered poor. The mortality rate is estimated to be 40 to 60% in dogs. Some dogs may relapse within the first year.

Follow-up Care for Dogs with IMHA