Risk of developing autoimmune and immune mediated disease following a diagnosis of myocarditis - a Danish nationwide...

Myocarditis is a severe condition characterized by myocardial inflammation. It is currently unknown if patients with myocarditis are at higher risk of developing autoimmune or immune mediated disease compared to the general population.

To estimate short- and long-term risk of developing autoimmune or immune mediated disease in patients with a first-time diagnosis of myocarditis.

We conducted a nationwide register-based cohort study using Danish national administrative registers. Endpoints were incidence of a composite of 35 autoimmune and immune-mediated diseases and all-cause mortality.

A total of 2671 patients with myocarditis between 2002 and 2020 in Denmark were matched on age and sex (1:5) with background population controls (n = 13,355). Median age was 46 years (Q1-Q3: 28-67), and 69.7 % were men. The 10-year cumulative incidence of autoimmune or immune-mediated disease was 7.2 % in the myocarditis cohort and 2.9 % in controls. The adjusted hazard ratio (HR) for autoimmune or immune-mediated disease ≤180 days of follow-up was 10.29 (95 % CI: 6.14-17.23) for patients with myocarditis versus controls, and 2.45 (95 % CI 2.02-2.97) >180 days (median follow-up time 9.4 years [Q1-Q3: 5.4-14.6]). Female patients with myocarditis had a 10-year cumulative incidence of autoimmune or immune-mediated disease of 10.7 %, compared to 4.4 % in controls. Corresponding figures for male patients with myocarditis were 5.6 % versus 2.2 % for male controls. All-cause mortality at 10 years was 26.7 % in the myocarditis group and 13.0 % in controls.

Patients with myocarditis had a significantly higher incidence of autoimmune and immune-mediated disease.