Autoimmune pancreatitis associated with inflammatory bowel diseases: A retrospectively bidirectional case-control study in China.

Objectives: Autoimmune pancreatitis (AIP) is a rare and enigmatic immune-mediated inflammatory disease. We aimed to investigate the prevalence, characteristics, and associated factors of AIP-inflammatory bowel disease (IBD) in China.

Methods: A retrospective bidirectional case-control study was performed. The diagnoses of IBD and AIP were made based on the European Crohn's and Colitis Organization guidelines and the International Consensus Diagnostic Criteria. IBD controls were matched by age, sex, and IBD type at a ratio of 1:4, while AIP controls were matched by AIP types.

Results: The age-standardized prevalence of AIP-IBD patients in the IBD and AIP population were 292.0 and 8151.93 per 100 000 population, respectively. IBD patients had a higher risk of AIP compared to non-IBD patients (odds ratio 8.4, 95% confidence interval 4.7-14.9, P < 0.0001), and AIP patients had a higher risk of developing IBD compared to the general population in China. The mean age at diagnosis of IBD and AIP was 34.83 years and 40.42 years. IBD was diagnosed before AIP in seven cases. The median total IBD and AIP duration was 43.5 months and 13.5 months. Use of mesalamine and tuberculosis were associated with AIP in IBD patients (P = 0.031). And fecal occult blood test was associated with IBD in AIP patients (P = 0.008).

Conclusions: Most AIP-IBD patients had ulcerative colitis and type 2 AIP. IBD patients are more likely to develop AIP compared to the general population, and vice versa. Use of mesalamine and tuberculosis infection were associated with AIP, and fecal occult blood test was associated with IBD.