Equine Liver Biopsy: Interpreting a Mixed Pattern
A 14-year-old Quarter Horse mare presents with weight loss over 6 weeks, icterus, and photosensitization on unpigmented muzzle skin. Serum biochemistry: GGT 210 U/L (ref 5-25), ALP 480 U/L (ref 80-220), AST 640 U/L (ref 200-400), SDH 45 U/L (ref 1-15), total bilirubin 95 umol/L with direct fraction 70 umol/L, bile acids 88 umol/L (ref <15), albumin 22 g/L (ref 26-37), globulins 48 g/L (ref 25-45). Ultrasound shows a small, hyperechoic liver with a nodular surface and no biliary dilation. A percutaneous liver biopsy is submitted. The pathologist must integrate the clinical picture with histology before signing out.
1. Using the biochemistry, predict the expected histologic pattern and explain how the enzyme and bilirubin data constrain your interpretation.
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The biochemistry indicates cholestasis plus hepatocellular injury plus portosystemic shunting with chronicity:
- GGT and ALP markedly elevated → cholestatic injury (biliary or canalicular).
- SDH and AST elevated → hepatocellular damage; SDH is liver-specific and short half-life, so it confirms active injury.
- Direct hyperbilirubinemia → impaired excretion, consistent with cholestasis or hepatocellular failure.
- Elevated bile acids + hypoalbuminemia + hyperglobulinemia → reduced functional mass and shunting; the low albumin argues for chronic disease.
Predicted histology: a chronic, likely fibrosing/bridging process - periportal fibrosis with bile duct proliferation, canalicular bile plugs, and hepatocellular degeneration. The photosensitization supports impaired biliary excretion of phylloerythrin.
Constraint: the absence of biliary dilation on ultrasound argues against extrahepatic obstruction; the nodular small liver favors chronic fibrosis/cirrhosis or chronic active hepatitis rather than acute toxic injury (which would show more diffuse necrosis with less fibrosis). The pathologist should not call this 'acute hepatitis' - the albumin and bile acid data demand a chronic interpretation.
2. The biopsy shows marked periportal fibrosis, bile duct proliferation, and bridging necrosis with scattered neutrophils. How do you reconcile this with the clinical picture, and what etiologies would you rank?
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Reconciliation: the histology matches the biochemical prediction of chronic cholestatic/fibrosing liver disease. Bridging necrosis with neutrophilic infiltrate and bile duct proliferation indicates ongoing active injury superimposed on chronic fibrosis.
Ranked differentials for an adult horse with this pattern:
- Pyrrolizidine alkaloid toxicity (Senecio, Crotalaria) - classic for bile duct proliferation, fibrosis, and megalocytosis; ask about pasture exposure and look for megalocytes.
- Chronic active hepatitis / immune-mediated - less common in horses but reported; bridging necrosis with lymphocytes/plasma cells.
- Cholangiohepatitis - neutrophilic infiltrate and duct proliferation fit; consider ascending biliary infection, though no dilation seen.
- Theiler's disease / viral hepatitis - usually more acute, but consider if recent equine serum exposure.
- Iron overload / hepatic necrosis from toxins (e.g., alsike clover, panicum) - check for pigment.
What I would add to the report: comment on presence/absence of megalocytes (supports pyrrolizidine), stain for iron (Prussian blue), and note that the small nodular liver plus low albumin indicates an irreversible, guarded prognosis. Recommend pasture investigation and client discussion of euthanasia versus supportive care.