The definitive diagnosis of IBD is obtained by histological examination of intestinal biopsies. Endoscopic biopsies are our first choice except when ultrasound examination has identified focal lesions in parts of the small intestine (that could not be reached with the endoscope) or raised a suspicion of other intra-abdominal abnormalities (especially in the liver or pancreas) that require multiple organ biopsies. We recommend endoscopic examination of the small and large intestine every time it is possible since in the authors’ experience some cases of colitis are observed without any suggesting clinical signs and small intestinal IBD can be observed with large bowel signs. When this “small and large approach” is not possible, the selection of the endoscopy procedure is made according to the clinical signs and history.
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As stated above, we use a parasiticide treatment (especially against giardia and whipworms) before admitting the dog for endoscopy. We have identified cases with negative fecal screening for giardia but where giardia trophozoites were observed on a fresh biopsy crushed in saline under a microscope coverslip. This approach is complementary to classical fecal screening and should be made in all cases.
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There is no typical pattern of the intestinal mucosa in IBD, it can range from normal to increased granularity and friability (Figure 6) with sometimes congestion or ulcers or a cobblestone appearance. The colonic mucosa in IBD ranges from normal to demonstrating a lack of submucosal vessels, or it may have a cobblestone appearance (Figure 7). Sometimes, focal proliferation can be observed, especially in eosinophilic enteritis. However, in one third to one half of the IBD cases, the mucosa is normal especially in cases exhibiting colitis. Furthermore, there is no correlation between the severity of the endoscopic findings and histological and clinical findings.
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Figure 6. Endoscopic view of the duodena mucosa in a dog with IBD. The presenting complaint was chronic vomiting. The duodenal mucosa was highly granular and very friable during biopsies. The histological diagnosis was moderate lymphocytic plasmacytic enteritis.
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Figure 7. Endoscopic view of the colon in a dog with chronic colitis. The presenting complaint was relapsing vomiting with occasional haematemesis. Signs of large bowel diarrhea with hematochezia have been observed for the 4 weeks preceding presentation. Note the lack of visualization of submucosal blood vessels and the digested blood adherent on the colonic wall. The final diagnosis was eosinophilic enterocolitis. The condition of the dog dramatically improved with an exclusion diet and one month of metronidazole treatment. No relapse has been observed after 2 years of follow-up.
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Histological diagnosis of IBD is quite challenging and strong interaction between the clinician and the pathologist is recommended to maximize the chances of a successful outcome. In order to increase the representivity of the samples, numerous multiple site biopsies (8 to 12) at each level are required.
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There is no clear consensus about IBD staging and recently an international group of experts has been created to obtain a world-wide standard for intestinal histological evaluation in dogs and cats (WSAVA Gastrointestinal Standardization Group). If the sample is appropriate, differentiation between IBD and tumors is usually possible. However, in cases with a heavy inflammatory infiltrate, the confident differential between lymphoma and severe lymphocytic plasmacytic enteritis can be difficult, particularly if the pathologist is working with endoscopic biopsy samples. The IBD is usually staged as mild (only infiltration of the lamina propria without fibrosis or architectural changes), moderate (infiltration of the lamina propria and moderate architectural changes of the mucosa) and severe (severe infiltration and architectural changes as villous atrophy, fusion or collapse, severe glandular hyperplasia or loss, fibrosis, ulcerations) (Figures 8 and 9). Generally, histology can classify IBD as lymphoplasmacytic, eosinophilic or (rare) the granulomatous form. Histiocytic colitis or eosinophilic granulomas can be also identified. Intestinal histology can help to rule out irritable bowel syndrome since the colonic biopsies are normal in this condition.
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Until recently, no clear correlation had been found between histology and clinical presentation in IBD. However, Jergens et al (see further reading) have developed a clinical index, the Canine IBD Activity Index, which correlates histological staging and some serum acute phase proteins. These observations promise a more standardized clinical staging of IBD for clinical studies but the prognostic value of this index remains to be determined.
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The main challenge in making a definitive diagnosis of IBD is to rule-out all cases of intestinal inflammation, since if they are diagnosed, it cannot be IBD. It is quite impossible to reach this condition in practical cases. However, the clinician should be sure that the main possible causes have been ruled out, and especially intestinal parasitism.
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Generally speaking, the histological grading of enteritis has no prognostic value on the outcome and IBD. Furthermore, the prognosis is quite good since the condition is not life-threatening. The protein-losing enteropathies and eosinophilic enteritis with deep intestinal wall infiltration carry the worst prognosis. Histiocytic colitis is given a very guarded to poor prognosis.
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Figure 8. Duodenal mucosa from a dog with lymphoplasmacytic enteritis (courtesy of M. Henroteaux). Moderate lymphoplasmacytic duodenitis with normal crypt/villus ratio and preserved epithelial differentiation. (Hematoxilin Eosin, x 400).
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Figure 9. Colonic mucosa from a dog with lymphoplasmacytic colitis (courtesy of M. Henroteaux). Severe chronic lymphoplasmacytic colitis with architectural distortion of the lower half of the crypts showing dilatation and indentation associated with highly regenerative signs. (Hematoxilin Eosin, x 200).
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