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

The study investigates the best method to diagnose equine dysautonomia, a deadly yet unexplained disease in horses that affects the digestive system. The research establishes that examination of 1cm long, formalin-fixed ileum biopsies offers a reliable method for diagnosis, demonstrating 100% accuracy in distinguishing the disease from similar gastrointestinal conditions.

Background of the Research

• The study focuses on equine dysautonomia, often called ‘grass sickness’. It’s a fatal disease in horses which impairs gastrointestinal mobility and results in symptoms similar to colic due to deterioration in the autonomic nervous system.
• Due to the similarity in symptoms, it is difficult to distinguish between grass sickness and colic. At present, the examination of ileal biopsies (sample tissues from the lowest part of the small intestine) retrieved through laparotomy (surgical incision into the abdominal cavity) is the most effective method to diagnose grass sickness ante-mortem (before death). However, the effectiveness of this method had not been critically evaluated before this study.

Key Findings of the Research

• After conducting postmortem simulations of biopsies from 23 cases of grass sickness and 11 cases of colic, the study found that formalin-fixed ileal biopsies of 1-cm length had 100% sensitivity and specificity for the diagnosis of grass sickness. This suggests that examining a small, specific piece of tissue from the ileum using this method can correctly and consistently identify the disease.
• The research showed that using larger biopsy samples or evaluating tissue from other regions of the small intestine (like the jejunum) neither added value nor improved accuracy.
• Comparatively, cryostat sections of ileum (thin slices of frozen tissues) of equivalent size also showed 100% sensitivity but only 73% specificity, meaning 27% of the cases could be wrongly categorized, potentially leading to unwarranted euthanasia.
• The research concluded that in spite of a somewhat slower return of results, formalin-fixed ileal biopsies of 1-cm provide a more accurate and reliable diagnosis for grass sickness than the alternative methods.