Introduction
Low grade dysplasia (LGD) is a key risk factor for development of high grade dysplasia (HGD) and colorectal cancer (CRC), in individuals with inflammatory bowel disease (IBD). Current clinical guidelines recommend that the detection of LGD should guide decision making, often leading to intensified surveillance or, in some cases, colectomy. As such, the detection of LGD in IBD imposes a considerable burden on both affected individuals and healthcare systems. The incidence, prevalence and treatment of IBD are continuously evolving. This may have influenced the incidence of IBD-related LGD and potentially its progression to HGD and CRC. Despite these developments, limited literature describes temporal trends in the incidence of IBD-related LGD, HGD and CRC, especially over the past decade, a period marked by the widespread use of biological therapies. Therefore, we aimed to utilize nationwide Danish health registers to describe trends over time in the incidence of IBD-related LGD, HGD and CRC.
Aims & Methods
We conducted a nationwide cohort study using data from Danish national health registers from 1990 to 2022. All Danish residents with a first-time diagnosis of either IBD, IBD-related LGD, HGD or CRC during this period were included. IBD-relation was established when a diagnosis of dysplasia or CRC was recorded within 180 days prior to, or at any time after, a first IBD diagnosis. HGD and/or CRC was defined as a composite endpoint, with the date assigned to the first occurring diagnosis if both were present. Incidence rates for IBD, IBD-related LGD, and HGD/CRC were calculated per 100,000 person years. Annual incidence rates and incidence rate ratios (IRRs) with 95 percent confidence intervals (CIs) were calculated using a Poisson approximation.
Results
During the study period, a total of 92,717 new cases of IBD, 8,406 cases of LGD, and 2,480 cases of HGD/CRC were identified.
The incidence of IBD per 100,000 person years increased markedly over time, rising from 30.36 in 1990 (95% CI: 28.89 to 31.91) to 59.71 in 2020 (95% CI: 57.76 to 61.73). A similar trend was observed for IBD-related LGD, with the incidence increasing from 0.33 (95% CI: 0.21 to 0.53) in 1990 to 10.41 (95% CI: 9.61 to 11.27) in 2020. For IBD-related HGD/CRC, the incidence rose from 0.12 (95% CI: 0.05 to 0.26) to 0.81 (95% CI: 0.61 to 1.07) in the same period. In the yearly incidence curves, the increase for both IBD and HGD/CRC appeared steady over time until a plateau was reached around 2008, whereas a distinct spike in LGD incidence was observed in 2014. This spike coincided with the introduction of a national CRC screening program in Denmark. Notably, the overall increase in IBD-related LGD far exceeded that of advanced dysplasia, with an IRR between 1990 and 2020 of 31.44 (95% CI: 28.01 to 35.28) for LGD, compared to 3.59 (95% CI: 3.35 to 3.85) for HGD/CRC.
Conclusion
The incidence of IBD, IBD related LGD, and IBD-related HGD/CRC has increased substantially in Denmark over the past 30 years. We observed a plateau in the incidence of IBD and IBD-related HGD/CRC within the last decade. Notably the overall increase in incidence was far more pronounced for IBD-related LGD, where we also observed a very notable spike in 2014, temporally aligned with the introduction of CRC screening in Denmark, this was not mirrored in the incidence of IBD-related HGD/CRC.