Study Case — A Schnauzer with Cholestatic Disease

Mindy R. Stelling, DVM; Bruce E. LeRoy, DVM, PhD, Heather Tarpley, DVM, and K. Paige Carmichael, DVM, PhD.

Class of 2005 (Stelling), Department of Pathology (LeRoy, Tarpley, Carmichael), College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7388

Signalment - Canine, Miniature Schnauzer, male, 13 year-old

Presenting problems - 10-day history of vomiting and lethargy

Medical history - Icterus

Laboratory Data -

Ultrasound Findings - Ultrasonography revealed a hyperechoic normal-sized liver, a hyperechoic right lobe of the pancreas with well-defined hypoechoic areas, and a dilated gallbladder with sludging present.

Radiograph Findings - Radiographs were within normal limits. There was no evidence of cholelithiasis.

1. Mildly decreased BUN and creatinine concentrations. A decreased BUN concentration can be due to a decrease in liver urea production, a decrease in protein intake, or from diuresis. The transient and mild nature of the decrease in both BUN and creatinine are most likely due to diuresis that was performed by the RDVM prior to referral.

2. Markedly elevated alkaline phosphatase activity. ALP is a membrane-bound enzyme, and is not commonly released into the serum with hepatic necrosis or cell injury. In this dog, the increase in serum ALP is most likely due to an increase in production of the hepatic isoform of alkaline phosphatase by the hepatocytes as a result of the increased intrabiliary pressure associated with cholestasis. Cholestasis also causes solubilization of the ALP molecules, contributing to the increase in the serum ALP activity. The increase in production develops slowly, with usually 24 hours before an increase in serum ALP is detected. Maximal enzyme activity is usually found after about 4-7 days. The half-life of the hepatic isoform of ALP in the dog is approximately 72 hours, therefore the serum activity may remain elevated for days beyond resolution of cholestasis. Levamisol testing may be useful to confirm that the principle isoform present is hepatic alkaline phosphatase.

3. Markedly elevated ALT activity. ALT is found in the cytoplasm of hepatocytes. Hepatocyte injury or necrosis will result in extracellular leakage of the enzyme. Leakage of ALT is detected in the serum much earlier than an increase in production of ALP, usually within a few hours of the insult. The highest ALT activity levels are seen with acute, massive hepatocellular injury. Lower levels may be attributed to more chronic diseases. ALT is a specific marker of hepatocellular injury in the dog, although occasionally severe muscle damage may also increase serum ALT activity. The half-life of ALT in the dog has been estimated to be 40-60 hours.

4. Mild sodium and chloride abnormalities. The electrolyte abnormalities in this patient were very mild. The three biochemical profiles demonstrated that the sodium and chloride concentrations were low or low-normal. These abnormalities can most likely be attributed to vomiting with loss of sodium and chloride and subsequent volume depletion leading to ADH release and increased water resorption by renal collecting ducts. Fluid lost through vomiting is usually iso- or hypotonic, and the response to volume depletion causes increased renal retention of water and/or increased water consumption which dilutes the remaining electrolytes.

5. Hypercholesterolemia. Cholesterol is produced primarily by the liver, and is either excreted in the bile unchanged or converted to bile acids. The increase in serum cholesterol in combination with the increase in serum ALT and ALP activities in this dog is most likely due to biliary obstruction causing a reflux of cholesterol into the serum, but dietary intake of cholesterol may also be contributing factor.

6. Bilirubinemia and icterus. Bilirubin is derived primarily from hemoglobin catabolism. Heme is converted to bilirubin in macrophages and excreted in a non-water soluble form (unconjugated) that is transported bound to albumin. Unconjugated bilirubin is transported to the hepatocyte through blood circulation, conjugated, and excreted into bile. An increase in serum bilirubin can result from an increase in production (hemolysis), intracellular disease (reduced hepatic functional mass or intrahepatic cholestasis), or a decrease in excretion (extrahepatic cholestasis). In this dog, the increase in bilirubin levels was attributed to extrahepatic cholestasis, most likely due to gall bladder obstruction caused by the sludge in the gallbladder seen on the ultrasound and histopathologic sections. Clinical observation of the increased bilirubin concentration (icterus) was noted in the yellow coloration of the skin, sclera, and mucous membranes.

7. Bilirubinuria. An increase in bilirubin concentration in the urine occurs when the serum levels are increased. Canines have a low renal threshold for bilirubin, and their kidneys can conjugate and excrete bilirubin, therefore bilirubinuria may be evident before bilirubinemia. In normal canines, there may be a trace amount of bilirubinuria present if the urine is concentrated.

8. Sludge in the Gallbladder. The sludge in the gallbladder seen on ultrasound is consistent with hepatobiliary disease. Rule-outs for hepatobiliary disease include cholangitis, cholangiohepatitis, pancreatitis, mucocele, neoplasia, or a cholelith. The ultrasonographic and radiographic patterns of the gallbladder were not thought to be consistent with a cholelith or neoplasia. A mucocele may be present, although the characteristic "kiwi fruit" sign was not observed. Pancreatitis was thought to be less likely since the amylase and lipase activities were within reference intervals.

Treatment - A cholecystectomy and a liver biopsy (Figures 1 and 2) were performed on 6/10/04, and no obvious stones or masses were found upon removal. Histologic findings were indicative of chronic hepatitis and extrahepatic biliary outflow obstruction.

Figure 1. H&E-stained section of the liver. Note the highly heavy infiltrations of inflammatory cells (arrowheads) and the proliferating bile ducts (arrows).	Figure 2. H&E-stained section of gall bladder. The luminal epithelium is proliferating in a papillary pattern. There is marked lymphoplasmacytic inflammation in the lamina propria (arrows).

An abdominal tap and blood chemistry were performed post operatively on 6/11/04.

Abdominocentesis -

Color/Clarity - red/cloudy

Nucleated Cell Count - 7,100 cells/ul

Protein - 3.9 g/dl

Differential - 59% Neutrophils, 8% lymphocytes, and 33% mononuclear cells.

Neutrophils are non-degenerate, no microorganisms seen

Diagnosis - exudate characterized by suppurative inflammation

Biochemical profile (partial) -

Test 6/11/04 Reference Range

ALP 4100 H (12-122 U/L)

ALT 464 H (12-108 U/L)

Cholesterol 647 H (129-264 mg/dl)

Bilirubin 11.5 H (0.0-0.2 mg/dl)

Interpretation - The abdominocentesis revealed suppurative inflammation of the peritoneal cavity, which is a common finding after abdominal surgery. No microorganisms were found in the fluid, and the neutrophils were not degenerate, therefore the inflammation was thought to be due to normal post-surgical inflammation and not reflective of clinically significant peritonitis.

The biochemical profile demonstrated that both the ALT and ALP values are still elevated 24 hours post-op as expected according to their half-lives. ALT has a shorter half-life than ALP, thus the serum level of ALT is expected to decline sooner than ALP. The cholesterol and bilirubin are still elevated, but should decline over the next few days as well.

Case Summary - The increased ALP activity and bilirubin concentration were suggestive of cholestatic disease, and the increased ALT activity was indicative of hepatocellular disease. Although both processes are occurring simultaneously, the massive increase in serum ALP activity followed by the increase in serum ALT activity is extremely suggestive of primary biliary disease. Biliary tract disease can cause subsequent hepatocellular damage and an increase in ALT activity. In this dog, the material in the gall bladder was presumed to have caused extra-hepatic cholestasis, which over time resulted in chronic hepatitis. The patient did not improve after surgery, and was euthanized.

References

Sodikoff CH: Laboratory Profiles of Small Animal Diseases: A Guide to Laboratory Diseases. St. Louis, Mosby-Year Book, Inc., 1995, pp. 3-11.

Thrall MA, Baker DC, et al: Veterinary Hematology and Clinical Chemistry, New York, Lippincott Williams & Williams, 2004, pp. 355-376.

Acknowledgment

Schnauzer Dog painting by John Robertson, from the Street Cred. Art website, is copyrighted and used with permission.

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