IBD patients at high myocarditis risk for up to 20 years

The risk of myocarditis appears to be elevated among patients with inflammatory bowel disease (IBD) for ≥20 years following diagnosis, suggests a study in Sweden. However, absolute risks remain low.

Patients with biopsy-confirmed IBD in Sweden (1969‒2017), general population reference individuals (n=391,344), and IBD-free full siblings (n=96,149) were included in this nationwide cohort study. Of the 83,264 patients with IBD, 24,738 had Crohn’s disease (CD), 46,409 had ulcerative colitis (UC), and 12,117 had unclassified IBD (IBD-U). Participants were followed until 2019.

The investigators used flexible parametric survival models to estimate the adjusted hazard ratios (aHRs) and cumulative incidence of outcomes, along with 95 percent confidence intervals (CI).

A total of 256 myocarditis cases (incidence rate [IR, 22.6 per 100,000 person-years) were recorded among IBD patients over a median follow-up of 12 years and 710 cases (IR, 12.9 per 100,000 person-years) in the general population (aHR, 1.55, 95 percent CI, 1.33‒1.81).

The myocarditis risk remained increased up to 20 years after the IBD diagnosis, which corresponded to one extra myocarditis case in 735 patients with IBD until then. Moreover, the risk increase occurred in both CD (aHR, 1.48, 95 percent CI, 1.11‒1.97) and UC (aHR, 1.58, 95 percent CI, 1.30‒1.93).

Notably, IBD showed a significant association with severe myocarditis (IR, 10.1 vs 3.5; aHR, 2.44, 95 percent CI, 1.89‒3.15), regardless of IBD subtypes (CD: aHR, 2.39, 95 percent CI, 1.43‒4.01; UC: aHR, 2.82, 95 percent CI, 1.99‒4.00; IBD-U: aHR, 3.14, 95 percent CI, 1.55‒6.33).

Similar results were observed in sibling comparison analyses.