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Category: Canine
Immune-mediated hemolytic anemia, autoimmune hemolytic anemia, IMHA, AIHA
AffectedAnimals:
Dogs of all ages may be affected with immune-mediated hemolytic anemia. Young to middle-aged female dogs are thought to be affected more commonly with immune-mediated disease than their male counterparts. Older dogs often have underlying or concurrent problems when IMHA develops. In some dogs, IMHA can precede the identification of cancer or other serious systemic diseases. Breeds including cocker spaniels, poodles, Old English sheepdogs, Lhasa apsos, and Shih-tzus may have a higher incidence of IMHA than other breeds.
Young dogs, especially beagles, Basenjis, and English springer spaniels, may have specific red blood cell enzyme abnormalities that result in hemolytic anemia at an early age; however, this anemia is not mediated by the immune system.
Overview:
Immune-mediated hemolytic anemia, or IMHA, is a relatively common syndrome in dogs. The immune system normally helps to protect the body from outside invaders. However, it can become active against normal cells or parts of the body, or against normal cells that have been altered by exposure to infectious agents, medications, or other disease processes in the body. Although a variety of factors may be associated with the development of IMHA, in most situations it occurs without an identifiable trigger or underlying cause. This is referred to as idiopathic immune-mediated hemolytic anemia. Affected dogs show the symptoms common to anemia due to any cause -- lethargy, weakness, increased respiratory rate, and pallor, or pale mucous membranes. In situations where the anemia develops rapidly, signs can be severe, with some animals actually presenting to the veterinarian in shock. In other cases, especially when the targeted red blood cells are in the bone marrow rather than in circulation in the blood vessels, the onset can be very slow and gradual.
There is no single test that is absolutely diagnostic for immune-mediated hemolytic anemia. It is usually diagnosed based on suspicion and the absence of any other specific causes for anemia. Bloodwork, x-rays, ultrasound, bone marrow examinations, and other diagnostic tests are part of the evaluation of an anemic dog. These studies are helpful in ruling out underlying or associated conditions, identifying additional abnormalities that require treatment, and in monitoring complications of the disease and its treatment.
Treatment of immune-mediated hemolytic anemia is aimed at restoring red blood cell numbers and trying to stop the ongoing destruction of additional red blood cells. Underlying causes or predisposing factors, when present, need to be addressed. If medications were being used prior to the diagnosis, they are usually stopped, in case they may have triggered hemolysis in the affected dog. Transfusions may be needed in severely ill dogs, but are generally useful only as a temporary measure unless the underlying cause of the red cell destruction is arrested. A large number of drugs have been used to suppress the immune response in dogs with IMHA. The cornerstone of treatment is prednisone. Only an attempt at treatment will provide an answer about the outcome for an individual patient with IMHA. There is an extremely wide range of severity of the condition, as well as an unpredictable response to treatment. Some animals are saved with relatively non-aggressive treatment and monitoring, while others succumb despite almost heroic efforts, either to the disease itself, complications like pulmonary blood clot formation, or side effects from the medications used to treat the disease.
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