S1178 Appendiceal Histologic Inflammation Correlates with the Extent of Active Colitis in Patients with Ulcerative Colitis

Introduction: There are emerging data to suggest that the appendix may be a priming site for pathogenesis in ulcerative colitis (UC) and curious findings that appendectomy may prevent UC or even provide some clinical benefit in active UC. However, the relationship and clinical relevance of active appendiceal disease and colonic disease extent is not known. Here we describe the correlation between appendiceal histological inflammation and the pattern of colonic histological activity. Methods: We performed a retrospective study of 275 UC patients who had colectomy, resection of the cecum, or right-hemicolectomy from 2000-2023 for medically refractory disease, neoplasia, or other (Figure 1). Pathology reports were reviewed for histologic involvement of the appendix (HIA) and pattern of histologic disease activity in colectomy specimens. Histologic involvement was categorized: appendix involved with active disease, appendix with fibrous obliteration or mucosal atrophy, or appendix without diagnostic abnormality. 15 patients whose appendix was not noted in the pathology report were excluded. Pattern of histologic activity was categorized into 4 groups according to the extent of colon involved: pancolitis, extensive colitis (disease extending beyond the splenic flexure but excluding cecum), left-sided colitis or proctosigmoiditis, or proctits. Demographic and clinical data were recorded. Results: 260 patients (111 pancolitis, 56 extensive colitis, 53 left-sided colitis or proctosigmoiditis, 2 proctitis) were analyzed. Active HIA was found to significantly correlate with active colitis regardless of extent (P=0.004) (Table 1). There was a significant correlation between active appendiceal disease and colonic extent of UC for pancolitis (P=0.00003) and left-sided colitis (P=0.003), but not for proctitis (P=0.502) nor for extensive colitis (P=0.751). Conclusion: Our data show that the presence of appendiceal inflammation correlates with the histologic activity of the colon and also associates with pancolitis or left-sided colitis. These findings are of interest and will inform additional studies of the clinical significance of appendiceal involvement and disease progression.Figure 1.: Flow-chart detailing patient inclusion description. Other indication for surgery include adenocarcinoma (n=2), inability to tolerate biologic therapies (n=1), colonic perforation (n=1), right colon mass (n=1), sigmoid colon cancer (n=1). Table 1. - Pathological findings of appendiceal involvement, stratified by histological extent of disease Active disease (n = 237) Pancolitis (n=111) Extensive colitis (n=56) Left-sided colitis and proctosigmoiditis (n=53) Proctitis (n=2) Appendix involved with active disease 99 (41.7) 61 (55.0) 20 (35.7) 10 (18.9) 0 Appendix with fibrous obliteration or mucosal atrophy 80 (33.8) 28 (25.2) 22 (39.3) 24 (45.3) 1 (50.0) Appendix without diagnostic abnormality 58 (24.5) 22 (19.8) 14 (25.0) 19 (35.8) 1 (50.0)