Evaluation of formalin-fixed ileum as the optimum method to diagnose equine dysautonomia (grass sickness) in simulated intestinal biopsies.

Equine dysautonomia, or grass sickness, is a frequently fatal disease of unknown etiology, manifested as poor gastrointestinal motility and colic as a result of degenerative changes in the autonomic nervous system. Examination of ileal biopsies collected at laparotomy is currently the best antemortem diagnostic method to distinguish equine dysautonomia from colic cases, which can present with similar signs, but their value has not been previously critically evaluated. Using simulated biopsies collected postmortem from 23 cases of equine dysautonomia and 11 of colic, the sensitivity and specificity of 1-cm long, formalin-fixed ileal biopsies was 100% for the diagnosis of equine dysautonomia. There was therefore no advantage to using larger biopsies or examining jejunum either in addition to or instead of ileal biopsies. Furthermore, although cryostat sections of ileum, 1-cm long, had a sensitivity of 100%, the specificity was only 73%, meaning that 27% of cases would have been misclassified, resulting in unnecessary euthanasia. Increasing the size of the cryostat or examining jejunum in addition to ileum cryostat sections did not significantly improve the specificity. Results of the current study indicate that in diagnostic practice, 1-cm long, formalin-fixed biopsies are likely to be the most suitable for accurate diagnosis, despite the slower turnaround time compared with cryostat sections.