Background: We wanted to estimate the incidence of irritable bowel syndrome (IBS) and functional dyspepsia (FD) in the general population, and the detection of colorectal tumor (CRT) and inflammatory bowel disease (IBD) after the diagnosis of IBS and FD.
Methods: Patients aged 20-79 years newly diagnosed with IBS (N = 2956) or FD (N = 9900), together with a comparison cohort randomly sampled from the general source population, were followed-up during a mean time of 3 years.
Results: We found an overall incidence of 10.3 per 1000 person-years for FD and 2.6 per 1000 person-years for IBS. There was a greater prevalence of depression, stress, fatigue, and pain disorders among IBS and FD patients than in the general population. During the 1st year after a diagnosis of IBS the cumulative risk of detecting CRT was close to 1% in IBS patients. After the 1st year the risk of CRT in IBS patients was close to that in the general population. We found a significantly increased risk of detecting IBD among patients initially diagnosed as having IBS (relative risk (RR), 16.3; 95% confidence interval (CI), 6.6-40.7), which was constant during all the follow-up period. No association was found between dyspepsia and CRT, or IBD.
Conclusion: IBS and FD shared some comorbidity features, yet demographics and incidence rates were different. Unlike the detection of colorectal tumor, the excess risk of IBD after an initial diagnosis of IBS was cumulatively increased during all the follow-up period. The continuously increased risk of IBD detection in IBS patients favors a true association between IBS and IBD.