Endoscopic Digestive Biopsies and their Clinical Usefulness in Horses

Presentation Description / Summary: The evaluation of gastro-intestinal (GI) biopsies is a multistep process that includes the review of a complete history including the horse’s diet and then the examination of the corresponding histology slides. Diagnostic parameters like hypoproteinemia with hypoalbuminemia, ultrasound findings of increased thickness of the small intestinal wall, and inconstant alterations of glucose or D-xylose absorption tests in combination with intestinal histopathology, can be useful to localize disease to the intestinal tract in the horse. Gastrointestinal biopsy, collected via endoscope, laparotomy or laparoscopy are useful diagnostic tools when faced with various digestive conditions in horses. The easy-to-use gastro-duodenoscope-rectoscope for duodenal or rectal biopsy sampling has become popular as it is also minimally invasive. The histological interpretation by the pathologist however, remains a challenge as baseline numbers for immune cells present in normal/healthy horses is poorly documented in the literature. Although guidelines have been developed for the assessment of GI biopsies in small animals (dog and cat), a standardized approach for the interpretation of the equine GI biopsy remains to be documented. The gastrointestinal mucosal immune system is complex and balances the tolerance of food antigens and commensal organisms with an adequate response to pathogens. Very little is known about the effect of environmental allergens or different types of diets on the intestinal immune cell expression. The characterization and quantification of intestinal immune cells could not only be helpful to differentiate disease status from normal, but could also help identify external factors that potentially modify the number of immune cells throughout the gut. Also, GI biopsy histology may be used in a research context to evaluate the effects of environmental factors (dietary constituents, pathogens, microbiota, etc) that may influence the gut response. In a horse with GI inflammation, the immune cell encountered within the mucosa in decreasing order are lymphocytes, plasma cells, eosinophils, macrophages and neutrophils. Specific cell infiltrations in the small intestine permits their classification into lymphoplasmacytic enteritis, eosinophilic enteritis, granulomatous enteritis or neutrophilic enteritis. Systemic diseases may also have a digestive infiltration form like seen in equine asthmatic patients that are seemed to have more T-lymphocytes in their digestive mucosa compared to control horses (personal data). A more finetuned characterization/quantification of immune cells in the intestines would allow for a more accurate biopsy interpretation by the pathologist who can now distinguish between normal or abnormal bowel infiltrates. This will help the clinician in the therapeutic/preventative management of the patient and may even provide a prognostic factor.