Postmortem diagnosis of idiopathic hyperammonemia in a horse

Lyndi L. Gilliam, Todd C. Holbrook, Julie E Dechant, Bill J. Johnson

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


A 6-year-old Quarter Horse stallion was referred to Oklahoma State University Veterinary Medical Teaching Hospital for evaluation of abdominal pain that developed after breeding activity earlier in the day. The horse developed diarrhea and progressively worsening neurologic signs (circling, ataxia, head pressing) within 22 hours of presentation and was subsequently euthanized due to severe self-destructive behavior. Antemortem biochemical and hematologic abnormalities included hypocalcemia but no evidence of hepatic disease. Idiopathic hyperammonemia and encephalopathy were suspected; cerebrospinal fluid (CSF) and aqueous humor were collected 10 hours postmortem for ammonia analysis using a colorimetric assay. Results were compared with those of 6 horses that also had been euthanized, for diseases unrelated to encephalopathy. Ammonia also was measured in plasma samples obtained antemortem. Ammonia concentrations in plasma (958 μmol/L), CSF (1566 μmol/L) and aqueous humor (1018 μmol/L) samples from the stallion were markedly increased compared to those in the 6 unaffected horses (plasma, 9-43 μmol/L; CSF, 370-532 μmol/L; aqueous humor, 70-483 μmol/L). Since the acute nature of hyperammonemic encephalopathy often does not provide sufficient time for an antemortem diagnosis, postmortem analysis of CSF and aqueous humor ammonia concentrations may be a useful alternative for documenting hyperammonemia in horses.

Original languageEnglish (US)
Pages (from-to)196-199
Number of pages4
JournalVeterinary Clinical Pathology
Issue number2
StatePublished - Jun 2007


  • Encephalopathy
  • Equine
  • Horse
  • Hyperammonemia

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • veterinary(all)


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