Veterinary Medicine - December 2008 - (Page 660)

CE PEER-REVIEWED IMHA: Diagnosing and treating a complex disease Differentiating IMHA from other causes of hemolytic anemia is challenging, but a careful diagnostic process will help you determine whether your veterinary patients will require long-term immunosuppressive therapy. Nicole Shaw, DVM, DACVIM, and Karyn Harrell, DVM, DACVIM A utoimmune hemolytic anemia, or immune-mediated hemolytic anemia (IMHA), is a complex disease in which hemolysis occurs because of antierythrocyte antibody production. This article explores the pathophysiology of primary and secondary IMHA and diagnostic and treatment options, as well as prognosis in dogs and cats. Our review of the recent literature regarding IMHA in veterinary patients reveals a focus on individual cases and a lack of controlled clinical studies, which makes a detailed review of IMHA triggers and treatment options dif cult. HEMOLYTIC ANEMIA VS. IMHA Many causes of anemia exist in dogs and cats, so a clear distinction should be drawn between hemolytic anemia and IMHA. Hemolytic anemia Hemolytic anemias are conditions in which red blood cells (RBCs) are destroyed at an accelerated rate and a normal regenerative response is seen in the bone Nicole Shaw, DVM, DACVIM Veterinary Emergency and Referral Group 318 Warren St. Brooklyn, NY 11201 Karyn Harrell, DVM, DACVIM Department of Clinical Sciences College of Veterinary Medicine North Carolina State University Raleigh, NC 27606 marrow. In these non-immune-mediated conditions, RBCs can be destroyed as a result of inherited membrane and enzyme defects, increased fragility from oxidative damage, or metabolic causes such as hypophosphatemia or water intoxication.1 Traditional immune-mediated mechanisms (immunoglobulins, complement) do not mediate lysis in hemolytic anemia. Instead, destruction occurs because of factors such as increased osmotic fragility, decreased RBC function in an alkalemic environment, or increased clearance from oxidative damage.1 Unlike the treatment of immune-mediated anemia, immunosuppression is generally not used to treat hemolytic anemias. Thus, it is imperative to investigate whether an anemia has an underlying cause before assuming it is immune-mediated. Below we discuss some of the common causes of hemolytic anemia. A more exhaustive list can be found in Table 1. Zinc and copper toxicosis. One of the most common causes of hemolytic anemia in dogs is zinc toxicosis from the ingestion of zinc-containing objects. High zinc concentrations can be found in pennies minted since 1983, board game pieces, zippers, zinc oxide ointment, and various other sources. Zinc toxicosis can cause a severe intravascular hemolysis that is associated with small amounts of Heinz body and spherocyte formation. Hemolysis from zinc toxicosis can be easily mistaken for IMHA if a survey abdominal radiographic examination is not performed. Treatment consists of removing the foreign object and providing supportive care. Copper toxicosis can also result in a marked intravascular hemolysis and methemoglobinemia.1 Kip Carter 660 December 2008 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - December 2008

Veterinary Medicine - December 2008 Contents Letters Thanking Our Valued Reviewers Practical Matters Idea Exchange Why Do Dogs and Cats Eat Grass? Managing Atypical and Critical Cases of Primary Hypoadrenocorticism in Dogs Behaviors Suggestive of Postoperative Pain in Cats What to Consider When Considering Digital Radiography Avoid Common Bandaging Mistakes in Dogs and Cats IMHA: Diagnosing and Treating a Complex Disease CE Form/Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - December 2008

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