Inflammatory Bowel Disease-Pathology



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Slide 59.   Pouchitis
There is considerable controversy over the nature and diagnosis of inflammation in ilea pouch anal anastomosis following total proctocolectomy.  Because the frequency of so-called “pouchitis” is considerably higher in patients with ulcerative colitis than in patients with non-inflammatory conditions requiring ileal retention reservoirs (such as familial adenomatous polyposis), inflammation in the former setting is often regarded as a manifestation of ongoing inflammatory bowel disease.  However, even in IBD patients, the causes of pouch inflammation are myriad, including both idiopathic (presumably IBD-related) and secondary process (including, but not limited to, infection, bacterial overgrowth, mechanical trauma/ischemia and de-novo inflammatory disease.  Because no one index of inflammation (clinical, endoscopic and histologic) provides a reproducible guide to management in these patients, various combinations of activities scores have been proposed.  The Pouch Disease Activity Index (PDAI) is one such approach.  The histologic score employed in this model emphasizes the degree of active inflammation and the extent of mucosal ulceration.  As this unit has emphasized, neither is selective for a particular disease process; hence, pouchitis, from a management point of view, is not evaluated in an etiologic context.  From a histologic point of view, pouchitis is a gradable phenomenon, based on extent of active crypt injury.  The image illustrates a mild degree of inflammation, to further emphasize the non-specific nature of this index.  Specific etiologies may be suggested from the pattern of crypt injury (acute self-limited, active chronic or ischemic), but even these characteristics lose disease selectivity in this clinical context.  Cultures of fecal material may nonetheless identify mucosal pathogens or evidence of overgrowth, while pre or post-anastomotic changes in non-reservoir mucosa may be useful in identifying features of ischemia.

It is important to determine, if possible, whether ongoing pouchitis after proctocolectomy for ‘ulcerative colitis’ represents recurrent disease (i.e., misdiagnosed Crohn’s disease) but, as already emphasized, this distinction remains problematic in endoscopic biopsies.  However, the classic stigmata of Crohn’s disease (epithelioid granulomas deep to mucosa and transmural lymphoid aggregates in areas uninvolved by aggressive mucosal injury) may be identified in surgically resected pouches.

Although chronic active pouchitis has been associated with colonic epithelial metaplasias, the overall risk for dysplasia in the ileal pouch anal anastomosis specimen does not approach that of ulcerative colitis.

Goldstein NS, Sanford WW, Bodzin JH: Crohn’s-like complications in patients with ulcerative colitis after total proctocolectomy and ileal pouch-anal anastomosis.  Am J Surg Pathol 1997; 21:1343-1353.

Petras RE: Role of the pathologist in evaluating chronic pouchitis.  In: Bayless TM, Hanauer SB, eds., Advanced Therapy of Inflammatory Bowel disease (Hamilton ON: BC Dekker, 2001), pp 229-232.

Shen B, Achkar J-P, Lashner BA, et al.: Endoscopic and histologic evaluation together with symptom assessment are required to diagnose pouchitis.  Gastroenterology 2001; 121:261-267.

Thompson-Fawcett MW, Marcus V, Redston M, et al.: Risk of dysplasia in long-term ileal pouches and pouches with chronic pouchitis.  Gastroenterology 2001; 121:275-281.