Comorbidity and mortality in adults with juvenile idiopathic arthritis: a nationwide Norwegian register-based matched cohort study.

OBJECTIVES: This population-based study assesses comorbidities, autoimmune conditions and all-cause mortality in (1) adults with juvenile idiopathic arthritis (JIA) against general population comparators and (2) adults with JIA with versus without recent disease-modifying anti-rheumatic drug (DMARD) exposure. METHODS: We included adults who, between 2009-2024, had ≥ 2 specialist health contacts with a JIA-specific ICD-10 code in the mandatory Norwegian Patient Registry (NPR). Each case was matched randomly, by age, gender and county of residence, to 10 general population comparators at the time of receiving the 2nd JIA diagnosis in adulthood. We compared 5-year retrospective comorbidity prevalences in descriptive analyses and prospective all-cause mortality in (1) adults with JIA versus comparators and (2) adult JIA with versus without recent DMARD exposure. RESULTS: Adults with JIA (N = 2932) had higher prevalence than comparators (N = 29 097) of ischemic heart disease excluding myocardial infarction (JIA vs. comparators (%): 1.0 vs. 0.6), hypertension (3.6 vs. 1.4), chronic kidney disease (0.5 vs. 0.2), type 1 diabetes (1.7 vs. 0.7), celiac disease (1.4 vs. 0.7), autoimmune thyroiditis (0.3 vs. 0.1) and autoimmune alopecia (0.4 vs. 0.1). Prospective all-cause mortality was higher in JIA than comparators (mortality rate 2.4 vs. 1.8 per 1000 person-years). In adult JIA, prevalences of comorbidities and autoimmune conditions as well as all-cause mortality, was similar in those with and without recent DMARD exposure. CONCLUSION: In this study we found an increased 5-year retrospective prevalence of several comorbidities and increased all-cause mortality in adults with JIA compared to population controls.