Differentiating inflammatory bowel disease (IBD) and alimentary small cell lymphoma (LSA), which are the predominant forms of chronic enteropathy in cats, is often challenging. Performing immunohistochemistry (IHC) and clonality testing (i.e., by PCR for antigen receptor rearrangement; PARR) as an adjunct to routine histopathological assessment may improve the diagnostic accuracy of endoscopic biopsy (EB) samples for making this differentiation. There is evidence to suggest that there is poor agreement between EB samples collected from the upper small intestines (USI) and the lower small intestines (LSI), and that both areas should be sampled in all patients. However, performing lower gastrointestinal endoscopy (LGE) along with upper gastrointestinal endoscopy (UGE) results in increased costs and anesthesia time compared to UGE alone. The goals of this study were to evaluate the diagnostic utility of IHC and clonality testing for the diagnosis of IBD and LSA in cats, to assess the level of agreement between EB samples from the USI and LSI, and to determine the diagnostic utility of procuring LSI samples.
A total of 62 cats with CE (gastrointestinal signs of > 3 weeks duration) were retrospectively (n = 19) and prospectively (n = 43) enrolled at the Veterinary Specialty Hospital, San Diego, CA. All cats had UGE and LGE performed with EB samples obtained from both sites. All cases were retrospectively or prospectively reviewed by a single board-certified pathologist (MRA) and were then categorized as “IBD”, “possible LSA”, “probable LSA”, or “LSA”. Samples were also submitted for IHC and clonality testing, as previously described.
Based on HE staining alone, 41/62 cats (66.1%) were classified as having IBD and 21/62 (33.9%) as having LSA. After consideration of IHC and clonality, 13/62 cats were classified as having IBD (21.0%) and 49/62 as having LSA (79.0%). Thirteen of 26 cases (50.0%) diagnosed as “IBD” and 15/15 cases (100%) diagnosed as “possible LSA” or “probable LSA” based on HE staining alone were subsequently diagnosed with LSA after the addition of IHC and clonality testing. Using Cohen’s Kappa statistic (k), agreement between USI and LSI samples was moderate (k = 0.65) based on HE staining alone, and also moderate (k = 0.68) after including IHC and clonality testing. For LSA cases diagnosed based on HE alone, there were 4/21 (19.0%) cases diagnosed from USI biopsy samples alone and 3/21 (14.3%) cases diagnosed from LSI biopsy samples alone. For LSA cases diagnosed after IHC and clonality, LSA was diagnosed in 7/49 cases (14.3%) from USI biopsy samples alone, but only 1/49 cases (2.0%) from LSI biopsy samples alone.
Our results show that the addition of IHC and clonality testing to HE staining increases the number of cases diagnosed with LSA. Further research is warranted to assess the diagnostic accuracy of IHC and clonality testing and to determine if a change in diagnosis correlates with patient outcome. Additionally, there was moderate agreement for the diagnosis of IBD and LSA in the USI and LSI. Samples from the LSI rarely added additional diagnostic information.
Internal Medicine Resident
Veterinary Specialty Hospital
Dr. Betty Chow grew up in Hong Kong, and received her veterinary degree from the University of Edinburgh, Scotland in 2010. She spent time in Hong Kong working under a VIN feline consultant before pursuing a small animal rotating internship at the University of Glasgow, Scotland from 2012-2013. She then flew across the pond for an internal medicine/oncology specialty internship at Mississippi State University from 2013-2014, and an internal medicine specialty internship at BluePearl Veterinary Partners in Grand Rapids, Michigan from 2014-2015, before starting her internal medicine residency at the Veterinary Specialty Hospital in San Diego in 2015. She enjoys many aspects of internal medicine, but has special interests in feline medicine, gastroenterology, and clinical nutrition.
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