Today's Veterinary Practice

SEP-OCT 2016

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tvpjournal.com | September/October 2016 | T O day' S Ve T erinary Prac T ice TH e ye LLOW ca T: dia G n OST ic & TH era P e UT ic ST ra T e G ie S Peer r eviewed 39 COMMON CAUSES OF PREHEPATIC HYPERBILIRUBINEMIA Infectious Disease Infectious disease is a relatively common cause of prehepatic hemolysis in cats. Mycoplasma species, particularly Mycoplasma haemofelis , can cause significant erythrocyte destruction, anemia, hyperbilirubinemia, and clinical disease. Outdoor, male, and/or shelter cats appear to be at increased risk, and coinfection with feline immunodeficiency virus (FIV) is common. 3-5 Concurrent diseases, immunosuppression, and stress appear to impact the course and severity of disease and outcome of treatment. An eventual recurrence of disease is seen with some frequency in those cats that show a clinical response to treatment. Feline leukemia virus (Fe l V) infection can trigger a host immune response that results in immune-mediated prehepatic erythrocyte destruction. This may be the result of a virus-induced expression of antigens on the red blood cell ( r BC) surface. Immune-mediated thrombocytopenia may accompany IMHA in cats with underlying Fe l V infection. 6 Cytauxzoon felis is transmitted by ticks (Am- blyomma americanum) and appears to be increasing in prevalence and geographical distribution in the United States, expanding from the southeastern portion of the country. r isk for infection increases with increased exposure to the tick vector, and the progression of clinical disease is rapid and often fatal. Babesia felis can cause severe prehepatic hemolysis and anemia in cats, but appears to be rare outside of costal South Africa. 7 Immune-Mediated Hemolytic Anemia Primary IMHA appears to be quite rare in cats. It is difficult to characterize feline IMHA or determine risk factors because of the paucity of cases in the literature, but younger male cats may be overrepresented. The prognosis is guarded, with a mortality rate of 25%. 8 Inherited Erythrocyte Disorders Erythrocyte pyruvate kinase (PK) deficiency is a very rare inherited disorder transmitted as an autosomal recessive trait, causing prehepatic hemolysis. Cats usually present as young adults, and the severity of the anemia and clinical signs is variable and may change over time, ranging from asymptomatic to hemolytic crisis. The disease is most frequently described in Abyssinian and Somali breeds but may also be present in a variety of other purebred and domestic shorthair cats. 9 Interestingly, Abyssinian and Somali breeds have also been shown to suffer from another inherited cause of prehepatic hemolysis: increased erythrocyte osmotic fragility. Genetic testing has been developed for screening cats for PK deficiency and is commercially available (vgl.ucdavis.edu/services/ pkdeficiency.php) Other Causes of Hemolysis Hemolysis secondary to hypophosphatemia has become rare due to heightened awareness, diligent monitoring, and proactive intervention during the treatment of diabetic ketoacidosis. Disseminated intravascular coagulation is also a rare occurrence, seen predominantly in the critical care setting, but serving as a reminder that prehepatic hemolysis can occur as a secondary consequence in a variety of diseases. Feline erythrocytes are susceptible to oxidative stress, and a large variety of toxins and drugs (including acetaminophen, benzocaine, methylene blue, phenazopyridine, onions/onion powder, propylene glycol, and propylthiouracil) can cause Heinz body anemia or hemolytic destruction of r BC membranes. COMMON CAUSES OF HEPATIC HYPERBILIRUBINEMIA Feline Hepatic Lipidosis Hepatic lipidosis appears to be a unique feline phenomenon, highlighting that hepatic metabolism in the cat is different from many other species. 10 Although feline hepatic lipidosis may be an idiopathic (Figure 2) and, therefore, primary problem, it quite frequently occurs secondary to another disease that caused the cat to stop eating. Figure 2. The liver (seen laparoscopically) of a cat with idiopathic hepatic lipidosis.

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