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Immune-Mediated Hemolytic Anemia - IMHA

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Overview

Immune-Mediated Hemolytic Anemia (IMHA) is a relatively common syndrome that is serious and often life-threatening. The immune system produces antibodies or molecules that normally target germs. In animals afflicted with IMHA, these antibodies attach and kill its red blood cells. As the red blood cells can no longer deliver oxygen to the tissues, the animal will not survive.

Breeds suffering from IMHA include Cocker Spaniels, Poodles, Old English Sheepdogs, Lhasa Apsos, Shih-Tzus, Irish Setters and Dachshunds. Cats are rarely afflicted. Middle-aged animals, more often female than male, from ages three to eight years are susceptible. More cases occur in spring and summer.

The two types of IMHA are Primary IMHA and Secondary IMHA. With Primary IMHA, a malfunctioning immune system creates antibodies that destroy red blood cells. With Secondary IMHA, an underlying problem such as systemic diseases, infection, parasites, cancer or reaction to a drug or vaccine triggers a change in red blood cells that stimulate the immune system to attack the animal’s cells. Older canines may have these underlying problems. IMHA may produce the following complications: clotting disorders, kidney failure, refractory anemia, and risk of infections. Causes are unknown.

Symptoms and Diagnosis

Symptoms of IMHA include lethargy, decreased appetite, weakness, exercise intolerance, increased respiratory rate, panting, pallor, and pale mucus membranes. Some animals appear jaundiced. As the haemoglobin from red blood cells breaks down, the pigment bilirubin circulates. Skin and eyes appear yellow. Urine may be dark yellow or orange. Rapidly developing hemolysis can make the urine red. Anemia that develops quickly can show severe signs such as shock. Inadequate oxygen delivery is the primary cause of these symptoms. Symptoms may be acute or more slow and gradual if onset. In onset cases, the targeted red blood cells are in the bone marrow, not in the blood vessels.

No single test exists as yet. Evaluating an anemic dog can involve bloodwork, x-rays, ultrasound, bone marrow exams and other tests. IMHA is often diagnosed on suspicion and with no specific causes.


Treatment

Treatment involves restoring the red blood cell numbers and halting the destruction of more red blood cells. Some dogs require relatively non-aggressive treatment. The severity of IMHA and the reaction to treatment can be wide. Drugs that suppress the immune response include corticosteroids such as prednisone or dexamethasone. Results should spare present red blood cells and allow the marrow to produce new red blood cells. Drug therapy over time includes a reduction of doses until the immune system is at a level and the packed cell volume is within a normal range. Transfusions offer a temporary stabilization for severely ill dogs by increasing the delivery of oxygen to tissues. Other canines will die from disease, complications such as blood clots, or drug side effects.

Supportive therapy addresses anemia, dehydration and complications. Intravenous fluid therapy can flush the kidneys of the damaging breakdown products of hemolysis, and prevent dehydration.

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