P0533 Extremely Rare Case of Isolated Colonic Inflammatory Cap Polyps in a Patient with Known Long-Standing Ulcerative Colitis

Abstract Background Inflammatory cap polyp (ICP) is a very rare benign colonic polyp, with fewer than one hundred reported cases worldwide, of uncertain origin. Typically found in adults around fifty years old, it affects the rectum or sigmoid colon. In its more common form (i.e., multiple ICP referred to as cap polyposis), it can mimic inflammatory bowel disease (IBD) due to symptoms like rectal bleeding, abdominal pain, and weight loss. Multiple forms of ICP can also be associated with severe hypoproteinaemia, as highlighted in a report employing scintigraphy with Tc-99m-labeled DTPA. Methods A 73-year-old H. pylori-negative woman with long-standing ulcerative colitis (diagnosed in 2016) and Alzheimer’s disease, under treatment with vedolizumab 300 mg every eight weeks, was referred to our digestive endoscopy unit for an endoscopic re-evaluation of her condition. The examination revealed severe pancolitis (E3 according to the Montreal classification, Mayo endoscopic score 3 at the rectum). During the endoscopic procedure, two sessile polypoid formations (0-Is according to the Paris classification), measuring approximately 10 and 8 mm, were en bloc resected using hot snare polypectomy, one from the transverse colon and the other from the descending colon (Figures A-D). Histological assessment confirmed the diagnosis of ICP due to erosive surface changes and granulation tissue with a “capping” morphology. Results In the context of the rarity of ICP, those associated with known IBD are indeed anecdotal. Moreover, the already reported cases that are clinically comparable to IBD have generally been associated with cap polyposis rather than isolated ICP. When subjected to thorough diagnostic evaluation, these cases have typically ruled out the diagnosis of IBD, revealing cap polyposis as merely a mimicking factor with a similar clinical presentation. In any case, our situation involves the rarer occurrence of isolated ICPs within the context of a long-standing, already-established diagnosis of ulcerative colitis and with an atypical (non-rectal) localisation. In the only reported case available in an IBD patient, it was a cap polyposis. Conclusion In conclusion, this case highlights that, although exceedingly rare, ICP can be associated with known IBD and, in addition to mimicking an IBD-like clinical picture (especially in the form of cap polyposis), it can also occur outside the typical location of the left colon. Furthermore, ICP may coexist in an isolated form without forming polyposis as isolated ICP. References Mason M, Faizi SA, Fischer E, Rajput A. Inflammatory cap polyposis in a 42-year-old male. Int J Surg Case Rep. 2013;4(3):351-353. doi:10.1016/j.ijscr.2012.12.0142. Batra S, Johal J, Lee P, Hourigan S. Cap Polyposis Masquerading as Inflammatory Bowel Disease in a Child. J Pediatr Gastroenterol Nutr. 2018;67(3):e57. doi:10.1097/MPG.00000000000013433. Valdés Delgado T, Barranco Castro D, Argüelles Arias F. Cap-Polyposis: A Cause of Treatment Failure in Ulcerative Colitis. Inflamm Bowel Dis. 2022;28(7):e108-e109. doi:10.1093/ibd/izac023

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