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35 JANUARY/FEBRUARY 2018 ● TVPJOURNAL.COM CONTINUING EDUCATION Ultrasonographic examination allows fine-needle aspiration of focal wall thickening and enlarged lymph nodes to provide samples for cytologic analysis. Cats with ultrasonographic evidence of muscularis propria thickening are more likely to have lymphoma than IBD. 45 Endoscopy and Mucosal Biopsy Endoscopic examination with mucosal biopsy is essential to confirm a diagnosis of IBD and determine the extent of disease. The most widely reported endoscopic abnormalities seen with canine and feline IBD include mucosal friability, increased granularity, and mucosal erosions ( FIGURE 5 ). 7,33,46 The association between endoscopic lesions and disease activity in small animal IBD has been investigated to a limited extent. In separate investigations, endoscopic abnormalities of the duodenum of dogs with IBD did not always correlate with clinical indices of inflammation. 33,47 The presence of severe mucosal lesions of the duodenum, but not the colon, was associated with a negative outcome in one study. 33 In contrast to dogs, cats with IBD have endoscopic abnormalities that correlate to both clinical disease activity and histopathologic lesions at diagnosis. 6 Standard mucosal biopsies of the stomach and duodenum alone may miss more distal sites (eg, ileal mucosa) of cellular infiltration. Ileal biopsies should be obtained in all dogs and cats to increase diagnostic yield whenever gastroduodenoscopy or colonoscopy is performed, especially as lymphoma is an important differential diagnosis in cats. 36 The need to perform ileoscopy may be guided by the presence or absence of hypocobalaminemia, because cobalamin is absorbed in the ileum. Histopathology Definitive diagnosis requires histopathologic evaluation of biopsy specimens. The microscopic findings in IBD consist of minimal to pronounced inflammatory cell infiltration, often accompanied by varying degrees of mucosal architectural disruption. Unfortunately, biopsy interpretation is notoriously subjective, suffering from extensive interobserver variability, the technical constraints of specimen size, and procurement/processing artifacts inherent in evaluation of endoscopic specimens. 48 One recent effort to standardize the assessment of GI inflammation resulted in a histopathologic monograph that defines numerous morphologic and inflammatory features in endoscopic biopsies. 39 However, even with this standardized scheme, there was very poor agreement between pathologists, 49 resulting in the design of a simplified model for IBD, currently under review. 50 Recent studies indicate that changes in mucosal architecture, such as villous morphology and goblet cell mucus content, are related to the presence and severity of GI disease. These studies have used quantitative, observer-independent variables (eg, inflammatory cytokines, intestinal mucus) to identify histopathologic correlates of disease. 6 In cats with signs of GI disease, villous atrophy and fusion correlate with the severity of clinical signs and degree of proinflammatory cytokine upregulation in the duodenal mucosa. 6 Architectural changes in the gastric mucosa correlate with cytokine upregulation in dogs with lymphocytic gastritis. 51 In the colon, loss of mucus and goblet cells correlates with the severity of disease in dogs with lymphoplasmacytic and granulomatous colitis. 52 FIGURE 5. Endoscopic images of dogs with IBD consistent with ( A ) increased small intestinal friability, ( B ) increased small intestinal granularity, and ( C ) intestinal mucosal erosions. ( D ) Endoscopic image showing the advancement of biopsy forceps to obtain partial-thickness biopsy samples in a dog with inflamed GI mucosa and IBD. Courtesy of Dr. Albert Jergens. A C B D