Diabetes mellitus, hyperadrenocorticism, hypothyroidism, and hyperthyroidism can cause changes in the liver.
HL can develop secondary to diabetes mellitus because of increased lipid metabolism and mobilization; hepatomegaly and increased liver enzyme activity are notable. Dogs with diabetes mellitus rarely manifest liver dysfunction unless they develop severe progressive VH and the hepatocutaneous syndrome (see Hepatocutaneous Syndrome in Small Animals). Most of these dogs have markedly increased AP and lesser increases in transaminase activity. Diabetic cats may develop increased ALT and AP activities, and may become hyperbilirubinemic with onset of HL. Diabetic animals have an increased risk of pancreatitis that may progressively cause EHBDO and cholangitis and are more susceptible to bacterial infections involving biliary structures (emphysematous cholecystitis, cholangitis).
Cats with hyperthyroidism usually develop increases in AP and ALT and rarely hyperbilirubinemia; liver function is usually normal. The underlying cause of altered enzyme activity is not fully understood but postulated to involve toxic effects of excessive thyroxine, malnutrition, cardiac dysfunction, induction phenomenon, and increased bone turnover. Liver enzymes return to normal with successful treatment; however, methimazole also can lead to a drug-associated hepatopathy that resolves on drug discontinuation.
Last full review/revision March 2012 by Sharon A. Center, DVM, DACVIM