Diagnosing feline small bowel disease: Do noninvasive tests make the cut?
Why they did it
Clinical signs of small bowel disease, especially weight loss and chronic or recurrent vomiting, are extremely common in cats. Previous studies have reported that chronic enteritis, specifically inflammatory bowel disease (IBD) and alimentary lymphoma, are common causes of small bowel disease in cats. In this retrospective case series, the authors sought to determine the prevalence of histologic abnormalities in cats with clinical signs of small bowel disease, identify the most common underlying causes and compare the accuracy of noninvasive diagnostic methods for differentiating among them.
What they did
Researchers evaluated medical records from cats examined for possible small bowel disease between July 2008 and November 2013. Compatible clinical signs included:
• Vomiting three or more times a month for at least three consecutive months
• Small bowel diarrhea lasting at least three weeks
• Losing at least 0.5 kg (1.1 lb) within the past six months.
In addition to clinical signs, cats included in the study had ultrasonographic evidence of intestinal wall thickening (≥ 0.3 cm in any location or ≥ 0.28 cm in two or more locations) and had full-thickness biopsy samples obtained from at least three small intestinal sites. Cats were classified as having segmental disease if an ultrasonographic examination revealed some measurements of wall thickness ≥ 0.28 cm and other measurements of wall thickness ≤ 0.25 cm.
Cats with suspected or proven hyperthyroidism were excluded. Given concerns for feline triaditis complex, pancreatic and hepatic biopsy samples were obtained in addition to intestinal biopsy samples in some cats.
Routine complete blood counts and serum chemistry profiles were performed in all cats and, in select cats, additional testing for serum feline pancreatic lipase (fPL) activity, cobalamin concentrations, and activity of the S-phase-speciï¬c protein thymidine kinase (TK) was also measured. Serum TK activity has been used in recent studies as a biomarker for lymphoma in cats, although whether serum TK activity can be used to differentiate gastrointestinal lymphoma from IBD remains unclear.
All biopsy samples were evaluated by a panel of four board-certified veterinary pathologists using standardized guidelines for the classification of intestinal disease. Results were considered ambiguous if changes were limited to only the epithelium and villi or in cases where T-cell mucosal infiltrates and architectural changes raised suspicion of lymphoma. These samples were submitted for testing with a polymerase chain reaction (PCR) assay for antigen receptor rearrangement.
What they found
The researchers included 300 cats (median age 11 years) with suspicion of small bowel disease. Among these, 249 (83%) had some degree of intestinal wall thickness of ≥ 0.28 cm and other measurements of wall thickness ≤ 0.25 cm, placing them in the segmental disease classification; 288 (96%) had histologic abnormalities, with chronic enteritis (n = 150) and lymphoma (n = 124) being most common. Of the 124 cats with lymphoma, small cell lymphoma was diagnosed in 107 of them. The authors identified more than one disease process in 33% (99/300) cats.
TK. Of the 31 cats in which it was measured, serum TK activity was above the reference range in 11 cats, but only six were found to have lymphoma based on histopathology. Eight cats with a histologic diagnosis of lymphoma had TK activity within the reference range. Thus, the overall sensitivity and specificity of TK activity in detecting lymphoma in cats with small bowel disease was determined to be 55% and 60%, respectively.
fPL. The serum fPL concentrations were found to be within the reference range in four of five cats found to have pancreatic lymphoma and in two of five cats with histologically confirmed pancreatic inflammation. Among the 126 cats with normal or nodular hyperplasia findings on pancreatic biopsies, 17 had presurgical fPL concentrations above the reference range.
Cobalamin. Serum cobalamin concentration was low in only two of the 78 cats in which it was measured—one cat had chronic enteritis and the other had lymphoma.
This study’s results suggest that cats with clinical signs of chronic small bowel disease and ultrasonographic intestinal thickening should undergo detailed diagnostic testing because they are likely to have clinically important and treatable disease. It is important to note that because only cats with ultrasonographic evidence of small intestinal thickening were included, the prevalence of chronic enteritis or lymphoma in cats with supportive clinical signs and normal ultrasonographic findings, is unknown.
The authors note that, while clinicopathologic testing is useful in identifying concurrent disease and gauging organ health, “our data indicated that serum TK activity, serum fPL concentration, serum cobalamin concentration, and results of preoperative CBC and serum biochemical proï¬les cannot reliably be used to differentiate intestinal lymphoma from chronic enteritis in cats suspected to have chronic small bowel disease.” Further, given that many cats had segmental disease based on ultrasonographic findings, full-thickness biopsy samples obtained via laparotomy or laparoscopy may be preferred over endoscopic biopsy samples to obtain a diagnosis.
Norsworthy GD, Estep JC, Hollinger C, et al. Diagnosis of chronic small bowel disease in cats: 100 cases (2008–2012). J Am Vet Med Assoc 2013;243(10):1455-1461.
Link to abstract: http://avmajournals.avma.org/doi/abs/10.2460/javma.243.10.1455