Microscopic Colitis and Risk of Venous Thromboembolism: A Nationwide Matched Cohort Study.

Introduction: Inflammatory diseases have been associated with increased risk of venous thromboembolism (VTE). However, data on VTE are lacking in large population-based cohorts of microscopic colitis (MC).

Methods: This study included all Swedish adults with incident MC without prior VTE (1990-2017; n = 12,489; follow-up until 2021). MC and subtypes (collagenous colitis and lymphocytic colitis) were defined from prospectively recorded colorectal histopathology reports from all 28 pathology departments in Sweden. Individuals with MC were matched for birth year, sex, calendar year, and county with up to 5 general population reference individuals (n = 55,809) without prior MC. Sensitivity analyses included full sibling comparisons and stricter definitions of VTE requiring a primary diagnosis of VTE and a prescription of anticoagulant medication. Incidence rates and multivariable-adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) for VTE events were calculated using Cox proportional hazards modelling.

Results: Over a median of 10.0 years of follow-up, 755 (6.0%; 11.3/1,000 person-years) incident VTE events occurred in individuals with MC and 2,674 (4.8%; 8.6/1,000 person-years) in reference individuals. Individuals with MC had a higher overall relative risk of any VTE event compared with reference individuals (aHR 1.21, 95% CI 1.11-1.32) including higher risk of pulmonary embolism (aHR 1.23, 95% CI 1.08-1.40), deep vein thrombosis of the legs (aHR 1.16, 95% CI 1.03-1.32), and other VTE events (aHR 1.31, 95% CI 1.08-1.58). The results remained robust in sensitivity analyses.

Discussion: In this population-based study, individuals with MC had a 21% higher risk of VTE compared with reference individuals, equivalent to 1 extra VTE event for every 37 MC individuals followed for 10 years.