Inflammatory bowel disease-specific findings are common morphological changes in the ileal pouch with ulcerative colitis

Why inflammation is common in ileal pouches with ulcerative colitis (UC) is unclear. We therefore clarified the morphological changes in pouches and afferent limbs (AL) of patients with UC and explored the relationship between these findings. We evaluated the morphological findings (histological and endoscopic inflammation as the Pouchitis Disease Activity Index [PDAI] histology subscore [hPDAI] and endoscopy subscore [ePDAI], inflammatory bowel disease [IBD]-specific findings using the IBD score [S(IBD)], colonic metaplasia using the colonic metaplasia score [CMS], and goblet cell [GC] ratio) in the pouch and AL of patients with UC. A total of 261 pouchoscopies were analyzed. The pouch body had a higher hPDAI (p < 0.001), S(IBD) (p < 0.001), CMS (p < 0.001), GC ratio (p < 0.001), and ePDAI (p < 0.001) than the AL. The hPDAI was correlated with the S(IBD) (Spearman’s coefficient r = 0.538; p < 0.001), CMS (r = 0.687; p < 0.001), and the ePDAI (r = 0.552; p < 0.001), but not with GC ratio (r = 0.175; p < 0.001) or the pouch usage duration (r = −0.057; p = 0.107). The incidence of histological inflammation was higher in specimens showing basal plasmacytosis with severe mononuclear cell infiltration (BP) than in those without BP (odds ratio [OR] 6.790, p < 0.001), BP was commonly found with crypt hyperplasia (OR 3.414, p < 0.001) and the crypt length correlated with neutrophil infiltration (r = 0.469; p < 0.001). Histological inflammation, colonic metaplasia, the GC ratio, endoscopic inflammation, and IBD-specific findings were commonly present in the pouch than in the AL. Histological inflammation occurs with IBD-specific findings and colonic metaplasia, and these signify endoscopic inflammation.