Emerging hepatobiliary diseases: know the syndromes
In veterinary medicine, patients often are diagnosed with a generalized hepatic disease or disorder.
Dr. David Twedt discussed these conditions in his presentation titled "Emerging New Hepatobiliary Disorders in the Dog" at the ACVIM 2006 Forum. He clinically and histopathologically categorized and defined four generalized syndromes:
Hepatocutaneous syndrome, or superficial necrolytic dermatitis, is a distinctive, crusting dermatosis in dogs and, less commonly, cats. The skin lesions have characteristic histological changes and patients generally have concurrent diseases such as diabetes mellitus, pancreatic neoplasia or severe hepatic disease. It is not known if the dysfunction of the liver is a mediator of the skin lesions or whether another metabolic condition is involved.Recent reports suggest that the syndrome can be associated with the chronic use of phenobarbital. Patients commonly present due to the abnormal skin appearance, including crusting plaques, erosions and alopecia. Blood work may demonstrate an elevation in alkaline phosphate (ALP) and elevated serum bile acids.
Ultrasonography may reveal a pathognomonic swiss-cheese, honeycomb or reticulated appearance to the entire liver, characterized by diffuse hyperechoic network surrounding hypoechoic areas.
It is believed the lesions are directly related to hypoaminoacidemia. This is supported partly by the fact that dogs fed a protein-deficient diet for a period of time will develop lesions in the liver consistent with changes seen in hepatocutaneous syndrome.
A recent study by Outerbridge et al. found that the plasma amino-acid concentrations of dogs with this condition were significantly lower than those of dogs with acute or chronic hepatitis. The cause of the deficient amino-acid concentration is not fully understood, but treatment is aimed at managing underlying disease.
Current therapy consists of either Aminosyn II (8.5%) or Aminosyn (10%). These are both amino-acid solutions that are administered intravenously at a dose of 24 ml/kg as a slow infusion. Encephalopathy can develop with rapid administration.
Frequency of administration can range from daily to weekly, depending on the response to therapy. Nutrition should be managed by supplementation of protein (often in the form of eggs) and calories. Fatty acids may be given as well as zinc and niacin. Antibiotics should be considered if secondary skin infection is present.
A gallbladder mucocoele is described as an enlarged and immobile gallbladder with fine striations (wagon-wheel appearance) visible on ultrasound. Small-breed dogs (Cocker Spaniels and Shetland Sheep Dogs) as well as geriatric dogs are over-represented. Clinical signs are generally non-specific but may include decreased appetite, vomiting and abdominal pain. Clinicopathologic abnormalities may include elevations in alkaline phosphatase, bilirubin and potentially alanine aminotransferase (ALT). Histopathological findings typically include biliary stasis and mucosal hyperplasia, which may be involved in the formation of a mucocoele. Patients present typically due to secondary effects of the mucocoele (complete or partial obstruction of the gallbladder), so it may be possible for a mucocoele to be found incidentally or to resolve on its own prior to diagnosis. However, due to the association with obstruction and even gallbladder inflammation and necrosis, cholecystectomy is considered the treatment of choice.
Evaluating the risk
Recent studies suggest that the prognosis may be guarded for the immediate post-operative period, although those that survive the early post-operative period generally have a good long-term prognosis. Risk factors include increasing age, gamma-glutamyltransferase activity, preanesthetic heart rate, blood urea nitrogen (BUN), phosphorus and bilirubin concentrations. It was found that the use of biliary diversion procedures was a risk factor for death, as was concurrent or resulting pancreatitis.
Hepatic portal vein hypoplasia, or microvascular dysplasia (MVD), is a congenital disorder associated with abnormal microscopic hepatic portal circulation. The defect results from abnormal embryologic development of the portal vasculature.