This large retrospective study identified subclinical IBD in FIT positive patients undergoing screening colonoscopy. The incidence rate within this group was higher than previously reported with CD being the most common subtype of IBD diagnosed.
The incidence of IBD is highest in the third and fourth decades of life, but can occur at any age.10 Several studies have reported a bimodal distribution of IBD, with 10–30% new diagnosis of IBD occurring at an older age in the population.11–13 The proportion of incidental endoscopic and histologic colitis in patients presenting for screening colonoscopies was 0.6% likely due to inclusion of microscopic colitis, ischemic colitis, and SCAD in the original cohort. The true proportion of patients with subclinical IBD in our study was comparable to 0.35% as reported in a Spanish cohort screened for FIT positivity.6 Other studies, with different methodologies, reported a wide range of 0.01–3% incidence of IBD in asymptomatic patients.4,5,7,14–16 Canada continues to have one of the highest rates of IBD in the world,2,10,17 including the highest incidence and prevalence of CD,18,19 which could also explain the higher incidence of IBD in the current study. The total incidence of IBD in populations screened in a FIT program followed by colonoscopy has been studied by a Spanish group,6 and the comparison of our results to the previous study are outlined in Table 3.
Table 3
Data comparison between studies comparing IBD incidence from FIT screening programs
| Rodriguez-Lago et al. | Bedi et al. |
n | 110 | 191 |
Median age | 57 | 58 |
Smoking history (%) | 10 | 12 |
Ulcerative Colitis (%) | 71.8 | 30.4 |
Crohn's Disease (%) | 21.8 | 57.1 |
IBDU (%) | 6.4 | 12.5 |
UC distribution | | |
Proctitis (%) | 32 | 25.8 |
Left-sided (%) | 33 | 37.9 |
Extensive/pancolitis (%) | 35 | 36.2 |
CD distribution | | |
Ileal (%) | 42 | 14.7 |
Colonic (%) | 37 | 45 |
Ileocolonic (%) | 21 | 40.3 |
Upper gastrointestinal tract (%) | 0 | 0 |
Perianal (%) | 0 | 0 |
TI intubation (%) | 38 | 71.2 |
Any treatment (%) | 73.6 | 64.9 |
Oral Mesalamine (%) | 57.2 | 48.7 |
Rectal Mesalamine (%) | 30.9 | 17.8 |
Steroids (%) | 14.5 | 18.3 |
Azathioprine (%) | 5.5 | 6.8 |
Methotrexate (%) | 0.9 | 2.6 |
Biologic (%) | 1.8 | 17.8 |
Surgery (%) | 1.8 | 2.1 |
Follow-up period, median (months) | 25 | 25 |
Male predominance has been established for IBD in the older population and is consistent with the sex distribution in our study.4,7,20 Global variation in the incidence of subclinical IBD in this age category remains unknown. Whilst the incidence of IBD is increasing worldwide, European and North American countries still have a higher prevalence of IBD, as compared to Asian, African, and South American countries.10 The incidence rates of IBD in immigrant populations in Canada to those in children of immigrants who were either born in Canada or moved to Canada at a very young age have been investigated. It was reported that although the risk of IBD in immigrants is low, it was increased in children who were born in Canada or moved there at a young age.21 Our study offers a unique perspective as BC, Canada, is home to a wide ethnic diversity with high immigration rates from all over the world. This is likely attributable to the collective effects of genetic factors, environmental triggers, microbiome and diet, and innate and adaptive immunity in the development of IBD.
IBD is classified into UC, CD, and IBDU based on the distinctive endoscopic and histological findings. UC has been identified as the most common IBD subtype in the older population, especially amongst those with subclinical disease.4–7,12,22 Contrary to published literature, our study demonstrated a higher incidence of subclinical CD compared to UC in this group. This is consistent with the findings by Coward et al., who compared rates of CD and UC, in all ages, across various Canadian provinces, and found higher rates of CD compared to UC.23 The proportion of colonoscopies with terminal ileal intubation was high, possibly prompted by findings of segmental colitis, thus leading to a confirmation bias, in the diagnosis of ileitis. However, it is possible that cases of isolated ileitis went undetected in patients who did not have ileal intubation during colonoscopy. Significantly, the incidence of patients diagnosed with IBDU is similar to rates reported in literature.
Most patients in our study with CD were found to have colonic CD, and pancolitis was present in almost the same proportion of patients as left-sided colitis in those with UC. This is consistent with findings of Li et al. who performed polygenetic risk scores (PRS) for patients with CD across various ages and demonstrated low PRS scores for older patients.24 They also noted that patients with late onset CD diagnosis were more likely to have colonic CD, with a distinct disease location, disease behaviour, and management compared to younger patients diagnosed with CD.24 Therefore, late onset CD could be a distinct disease milieu, which may be more similar to pancolonic UC diagnosis in older patients.
Treatment recommendations for patients with symptomatic IBD have been well-established.25–28 However, little is known regarding the role of treatment or appropriate monitoring in patients with subclinical disease, especially in older patients. Early initiation of disease modifying therapy, such as, anti-tumour necrosis factor or other biologic agents, has been beneficial in slowing further disease progression and symptom resolution.29 Our study had a lower treatment initiation rate of 65% compared to 88% in a similar study performed by Rodrigues-Lagos et al (Table 3).6 This may be due to a lack of guidelines and drug efficacy trials for treatment of older patients with IBD, who may be more prone to adverse effects from various medications.30 Benchimol et al. studied the management of older patients with IBD in Canada, USA, UK, and Denmark and attributed the variability to patient or physician preference, concerns about adverse events and poly-pharmacy, differences in quality of care, adherence to clinical guidelines, or pharmaceutical industry marketing.31 Bernstein et al. studied younger patients with IBD and showed a higher comorbidity burden in those with IBD compared to matched controls.32 This indicates that the management of potentially co-morbid older patients with an initial subclinical IBD diagnosis is likely more nuanced than for patients with clinically symptomatic disease. Additionally, 8 patients in our study required 2 or more biologics, with 2 patients requiring 4 biologics for disease management. In addition to medical management, 4 patients required surgical intervention for IBD related stricture or medically refractory colitis in our study. This is substantial given that 3 of the 4 patients who required surgery did not have any symptoms at the time of screening colonoscopy. It is unclear whether early advanced medical treatment could have avoided the need for surgical intervention in those patients.
Strengths and Limitations:
The strengths of this study include the relatively large sample size and ethnic diversity of the study population. The limitations include a retrospective study design, a retrospective characterization of IBD subtype that may not capture disease evolvement over time, and inability to review the entire cohort of BCCSP patients diagnosed with colitis. As BC does not have a common electronic medical record available for research purposes, it was not feasible to involve all 130 colonoscopy sites. Exclusion of sites from smaller or remote communities introduces potential bias as patient characteristics and management may differ. Finally, lack of demographic data and information regarding generational residency in Canada or North America limited the evaluation of role of genetics in IBD incidence.