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Background: Anti-TNFα agents have revolutionised management of chronic inflammatory diseases. Paradoxically, these agents might provoke development of de novo autoimmune diseases., Aim: To examine whether there is an increased risk of developing Crohn's disease (CD) and ulcerative colitis (UC) while under treatment with anti-TNFα agents for diseases other than inflammatory bowel disease (IBD) METHODS: A nationwide cohort study, based on Danish health registries, of all patients who utilised anti-TNFα agents for non-IBD indications. Included were patients, who had diseases for which anti-TNFα agent is indicated (rheumatoid arthritis, psoriasis/psoriatic arthritis, ankylosing spondylitis, others). The observation period for development of de novo IBD started from 2004. Exposed patients had received at least one dose of anti-TNFα., Results: In total 17 018 individuals with autoimmune diseases were exposed to anti-TNFα (the vast majority had infliximab, etanercept and adalimumab), and 63 308 individuals were not. Patients treated with etanercept had an increased risk of being diagnosed with CD and UC while under treatment, adjusted hazard ratio 2.0 [95% CI: 1.4-2.8] and 2.0 [95% CI: 1.5-2.8], respectively. The corresponding hazards ratios for infliximab were 1.3 [95% CI: 0.8-2.2] and 1.0 [95% CI:0.6-1.6], and for adalimumab 1.2 [95% CI: 0.8-1.8] and 0.6 [95% CI: 0.3-1.0]., Conclusions: Patients treated for autoimmune diseases with anti-TNFα had an increased risk of being diagnosed with CD or UC while under treatment with etanercept. The nature of this association is uncertain. This finding has relevance to clinical care and insights into common mechanisms of the pathophysiology of these diseases., (© 2019 John Wiley & Sons Ltd.)

Background: The relationship between appendectomy and Crohn's disease is controversial. A Swedish-Danish cohort study was conducted to assess the risk of developing Crohn's disease after an appendectomy., Methods: 709 353 appendectomy patients in Sweden (since 1964) and Denmark (since 1977) were followed for first hospitalisations for Crohn's disease to 2004. Standardised incidence ratios (SIR) served as relative risks., Results: Overall, 1655 Crohn's disease cases were observed during 11.1 million person-years of follow-up. Whereas appendectomy before the age of 10 years was not associated with the risk of Crohn's disease (SIR 1.00; 95% CI 0.80-1.25), the overall SIR of developing Crohn's disease was 1.52 (95% CI 1.45-1.59), being highest in the first 6 months (SIR 8.69; 95% CI 7.68-9.84). SIR diminished rapidly thereafter, with the risk of Crohn's disease reaching background levels after 5-10 years for Crohn's disease overall, as well as for Crohn's ileitis, ileocolonic Crohn's disease, Crohn's colitis and other/unspecified Crohn's disease. A long-term increased risk of Crohn's disease up to 20 years after the appendectomy was seen only in appendectomy patients without appendicitis or mesenteric lymphadenitis., Conclusion: The transient increased risk of Crohn's disease after an appendectomy is probably explained by diagnostic bias.