Overview of Immune Mediated Hemolytic Anemia in Cats (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.
Below is an overview about Immune mediated hemolytic anemia (IMHA) in cats followed by detailed information about the diagnosis, treatment and prognosis of this serious condition.
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. It is most commonly reported in young cats and there is known breed predisposition in cats.
IMHA is a rapidly life-threatening disease. Even with appropriate treatment, this disease can be fatal.
What To Watch For
Diagnosis of IMHA in Cats
Your veterinarian will recommend the following tests:
Treatment of IMHA in Cats
Home Care and Prevention
It is crucial to administer all prescribed medications as directed. Even a few missed doses can have serious consequences.
Because we do not understand what causes IMHA, there are no known preventive measures.
In-depth Information on Feline Immune Mediated Hemolytic Anemia
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 animal's own cells rather than just germs. Sometimes the attack on the animals 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.
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)
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 Diagnosis of Feline IMHA
In-depth Information on Treatment of Feline IMHA
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 cats 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.
Prognosis for Feline IMHA
The prognosis depends on the pets response to treatment and the underlying cause for the disease. The prognosis is generally considered poor in cats.
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not rapidly improve.