On guard for hepatobiliary diseases in dogs
Q. Could you review some new hepatobiliary diseases in dogs?
A. Dr. David C. Twedt gave a lecture on emerging new hepatobiliary disorders in the dog at the 2006 American College of Veterinary Internal Medicine Forum. A review of the lecture is provided.
Hepatocutaneous syndromeHepatocutaneous syndrome, known as superficial necrolytic dermatitis, is an uncommon disease observed in middle-aged to older dogs.
The skin lesions have characteristic superficial necrolytic dermatitis or necrolytic migratory erythema. When these characteristics are combined with hepatic changes, it typifies this syndrome. The liver has mistakenly been described by some as cirrhotic because of the nodular appearance of the liver. The hepatic changes are best described as an idiopathic hepatocellular collapse with nodular regeneration. Changes generally are devoid of major inflammation. The hepatic nodular regeneration consists of vacuolated hepatocytes. To date the pathogenesis of the hepatic disease is unknown. Nor is it known if the liver dysfunction is the major mediator of the necrolytic skin lesions or whether another metabolic disease produced both the skin and hepatic lesions. Affected dogs almost all have pronounced reductions in amino acid and albumin concentrations. Diabetes mellitus occurs in some dogs. Recently hepatocutaneous syndrome has been associated with chronic long-term phenobarbital therapy.
Most dogs are presented because of the atypical skin disease. Abnormal serum liver enzymes are identified and, in most, serum ALP and bile acids are increased. The serum albumin is typically below normal and almost every affected dog is hypoaminoacidemic. The liver has a characteristic ultrasound appearance, looking like "Swiss cheese" due to the hypoechoic nodules.
It is thought that the necrolytic skin lesions are directly related to the hypoaminoacidemia, which may be responsible for the hepatic changes as well. This is supported in part by observations that dogs fed a protein-deficient diet for prolonged periods develop hypoalbuminemia and hepatic changes that resemble hepatic changes described in the hepatocutaneous syndrome; however, skin lesions were not observed. The importance of hypoaminoacidemia in this disease is further supported in that administration of intravenous amino-acid solutions transiently improved the skin lesions in many but not all dogs. The cause of the amino acid deficiency is unknown. The affected dogs appear to have been fed adequate protein-content diets. The prognosis for this disease is grave and invariably most succumb either due to liver dysfunction or to the severity of the skin lesions, or both.
Our current therapy includes administration of intravenous amino acid solution — approximately 500 milliliters of aminosyn (10% solution, Abbott) over eight to 12 hours. If administered too rapidly, hepatic encephalopathy can occur. Repeated infusions are given weekly. If after four weekly amino acid infusions and if there is no improvement, it is unlikely the dog will respond to therapy. With a positive response, the amino-acid infusions are given as needed. In addition, the dog is given a dietary protein supplement of egg yolks (as an amino acid source) and other protein supplements. Additional support includes antibiotics if a secondary skin infection exists, omega 3 fatty acids, ursodeoxycholic acid, vitamin E and/or zinc.
Gallbladder mucocele is seen in an enlarged gallbladder with immobile stellate or finely striated patterns within the gallbladder on ultrasound study. Changes often result in biliary obstruction or perforation. Smaller breeds and older dogs were over-represented, with Cocker Spaniels being most commonly affected. Most dogs are presented for nonspecific clinical sign,s such as vomiting, anorexia and lethargy. Abdominal pain, icterus and hyperthermia are common findings. Most have serum elevations of total bilirubin, ALP, GGT and variable ALT. Ultrasonographically, mucoceles are characterized by the appearance of stellate or finely striated bile patterns (wagon wheel or kiwi fruit appearance) and differ from biliary sludge by the absence of gravity-dependent bile movement. The gallbladder-wall thickness and wall appearance are variable and nonspecific. The cystic, hepatic or common bile duct may be of normal size or dilated, suggesting biliary obstruction. Gallbladder-wall discontinuity on ultrasound study indicates rupture, whereas neither of the bile patterns predicted the likelihood of gallbladder rupture. Mucosal hyperplasia is present in all gallbladders examined histologically, but infection is not present with all cases, suggesting biliary stasis and mucosal hyperplasia as the primary factors involved in mucocele formation. Cholecystectomy is the treatment for mucoceles.