Autoimmune Thyroid Diseases and Microscopic Colitis: A Nationwide Matched Case-Control Study in Sweden

Context Microscopic colitis (MC), comprising collagenous colitis (CC) and lymphocytic colitis (LC), is an inflammatory condition of the colon, characterized by watery diarrhea. Previous studies suggest an association between autoimmune thyroid diseases (AITDs) (Hashimoto thyroiditis and Graves disease) and MC; however, large-scale histology studies are lacking.Objective To assess the association between AITDs and future onset of MC.Methods We conducted a nationwide, matched case-control study. Patients with biopsy-confirmed MC diagnosed between 2006 and 2017 were identified through the population-based histopathology cohort ESPRESSO. Data on AITDs and covariates were retrieved from Swedish national health care registers. Odds ratios (ORs) for MC associated with prior AITDs were estimated using conditional logistic regression. Sibling comparisons were performed to minimize shared genetic and environmental confounding.Results Among 10 301 MC cases and 48 712 controls, AITDs were significantly more prevalent in MC patients (12.0%) than in controls (7.8%), yielding an adjusted OR of 1.65 (95% CI 1.54-1.77). This association was attenuated but remained significant in sibling analyses (OR 1.26; 95% CI 1.11-1.43) The association was stronger in patients diagnosed with MC before age 50 (OR 2.41; 95% CI 2.02-2.89). Subgroup analyses revealed no difference between CC and LC or between sexes.Conclusion Individuals with AITDs are at an increased risk of developing MC. That this association was robust across various subgroups may be indicative of shared underlying mechanisms. Our findings highlight the importance of being vigilant of gastrointestinal symptoms in patients with AITDs and that patients with persistent symptoms despite achieving euthyroidism should be evaluated for MC.