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 vs without recent disease-modifying anti-rheumatic drug (DMARD) exposure. Methods: We included adults who, between 2009 and 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 second JIA diagnosis in adulthood. We compared 5-year retrospective comorbidity prevalences in descriptive analyses and prospective all-cause mortality in [1] adults with JIA vs comparators and [2] adult JIA with vs 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), coeliac 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 with population controls.