Results of histopathology, immunohistochemistry, and molecular clonality testing of small intestinal biopsy specimens from clinically healthy client-owned cats

Abstract

Background: Histopathology, immunohistochemistry, and molecular clonality testing are metrics frequently used to diagnose chronic enteropathy (CE) in cats. However, normal values for these metrics have been based mainly on samples from cats that were relatively young, specific pathogen-free, or both. Objectives: To describe results of histopathology, immunohistochemistry, and clonality testing of endoscopically-derived biopsy specimens of the upper small intestinal tract from a cohort of clinically healthy client-owned cats. Animals: Twenty clinically healthy client-owned cats ≥3 years of age. Methods: Tissue specimens were collected from the stomach and duodenum and evaluated single blinded by a board-certified pathologist. In addition, samples were evaluated by routine immunohistochemistry and clonality testing. Cats were followed after the procedure for signs of CE. Results: Integrated results from histopathology, immunohistochemistry, and clonality testing were interpreted as consistent with small cell lymphoma (SCL; n = 12), emerging SCL (n = 1), lymphocytic enteritis (n = 6), and pseudoclonality (n = 1). On follow-up, 3 cats eventually developed clinical signs of CE, of which 2 were euthanized 295 and 654 days post-endoscopy. The remaining 17 cats did not show clinical signs of CE after a median of 709 days (range, 219-869 days). Conclusions and Clinical Importance: Intestinal biopsy specimens from clinically healthy client-owned cats commonly had abnormal findings on histopathology, immunohistochemistry, clonality testing, or some combination of these without apparent clinical relevance. Current diagnostic metrics for diagnosing CE in cats may need modification to be applicable to the general population of cats.