Introduction: Incidentally diagnosed inflammatory bowel disease (IBD) can be found in asymptomatic individuals undergoing endoscopic examinations performed for various reasons such as colorectal cancer (CRC) screening. We aimed to characterize the prevalence of incidental IBD in individuals undergoing non-diagnostic colonoscopy and describe its clinical characteristics, disease course, and medium to long-term outcomes.

Methods: We conducted a retrospective cohort study including all asymptomatic adults who underwent colonoscopy for CRC screening or polyp surveillance between 2009 and 2023. Incidental IBD was considered any case with endoscopic and histologic findings suggestive of IBD. The endoscopic lesions considered to be suggestive of IBD were erythema, erosions, loss of vascular pattern, ulcerations, strictures, and/or pseudopolyps. On the other hand, the microscopic criteria were transmural inflammation, non-caseating granulomas, ulcers, crypt distortion and abscesses, cryptitis, Paneth cell metaplasia, and basal plasmacytosis. Additional clinical data regarding patient and disease characteristics was also collected. Tests for categorical variables were performed using the Fisher-Freeman-Halton Exact Test, while for quantitative variables the ANOVA and Kruskal-Wallis Test were utilized. All statistical analyses were conducted using R, with significance at p < 0.05.

Results: Out of 40,573 colonoscopies, a total of 60 patients with incidental IBD were identified: 40 patients (67%) with Crohn’s disease (CD), 10 (18%) with ulcerative colitis (UC), and 10 (18%) with IBD- unclassified (IBD-U). The mean age at diagnosis was 54.6 years, 52.8 years, and 55.7 years, respectively. There was a female predominance in UC compared to CD or IBD-U (70 vs. 48% and 60%, respectively). Most CD patients presented with ileal (L1) involvement and inflammatory (B1) behavior (98%), while 60% of UC patients exhibited extensive (E3) disease. UC and IBD-U patients had lower hemoglobin values than those with CD. Follow-up data was available from 27 patients (45%), after a mean follow-up of 27.9 ± 34.7 months in CD patients, 20% (N = 8) developed new-onset symptoms (diarrhea [38%], abdominal pain [37.5%], bloating [25%], fatigue [12.5%], weight loss [13%]), while only one patient (10%) with UC reported symptoms (diarrhea and abdominal pain). A total of 5 patients (8%) initiated medical therapy, in most cases after symptom onset. Two patients (5%) with CD received oral corticosteroids, one (3%) with CD received sulfasalazine, and two patients (20%) with UC were started on oral mesalamine. No hospitalizations or surgeries were noted.

Conclusions: In our experience, the prevalence of incidental IBD was 0.2% with two-thirds receiving a diagnosis of ileal CD with inflammatory behavior. A low proportion of patients developed symptomatic disease (20% for CD and 10% for UC) after 2 years of follow-up and generally had milder disease course.