Equine Health Update EHU 2020 Issue 01 | Page 48

EQUINE | CPD Article Clinical Pathology Basics for Equine Practitioners - Liver Disease Dr Rick Last – BVSc; M.Med.Vet (Pathology) Consulting Specialist Veterinary Pathologist Introduction Clinical signs of liver disease in equines are often vague and non-specific, although there are some clinical symptoms which are highly suggestive of a primary hepatopathy, and these include hepatomegaly / microhepatica, icterus, ascites and hepatic encephalopathy. The more common non-specific clinical signs include depression, weight loss, anorexia, abdominal pain, polyuria/polydipsia (PU/PD). These non-specific signs are also frequently observed with many other diseases. In the early stages of liver disease, sub-clinical presentation with non-specific signs is common, while specific hepatic symptoms are rarely observed. Therefore, serum biochemical profiling of hepatic function is extremely useful in identifying the presence or absence of liver disease and whether any hepatic dysfunction is acute or chronic. These biochemical changes may result from either primary liver disease or are secondary to other primary non-hepatic diseases. However, when these biochemical tests are interpreted in conjunction with clinical signs and other laboratory analyses, they allow for recognition of pattern changes, from which a number of diagnostic, prognostic and treatment decisions can be made. 48 The diagnosis of liver disease is based on abnormalities in serum enzymes that are partly or exclusively associated with hepatocytes and/or epithelial cells lining the biliary tree as well as some analytes that assess liver functionality and other more general indicators of inflammation. Hepatic enzymes are divided into two categories • Hepatocellular leakage enzymes (cytoplasmic, mitochondrial). • Induced enzymes. Hepatocellular leakage enzymes are soluble enzymes that occur normally in the cytoplasm (aspartate aminotransferase AST; alanine aminotransferase ALT, sorbitol dehydrogenase SDH) or mitochondria (glutamate dehydrogenase GLDH and aspartate aminotransferase AST) of hepatocytes. They are released with hepatocellular membrane damage with sublethal injury or hepatocellular necrosis. The serum activity of these enzymes depends on the number of hepatocytes injured, the severity of the injury and the half-life of the enzyme involved. Induced hepatic enzymes (alkaline phosphatase ALP; γ-glutamyl transferase GGT) are typically membrane- bound and not released into the serum with increased membrane permeability. Increased serum enzymatic • Equine Health Update •