Background: Adults with juvenile idiopathic arthritis (JIA) carry the burden of cumulative disease activity over years. Like adult-onset inflammatory joint diseases (IJDs) such as rheumatoid arthritis, axial spondyloarthritis and psoriatic arthritis, JIA is characterized by chronic autoimmune joint inflammation [1]. These adult-onset IJDs have been associated with an increased risk of major comorbidities like cardiovascular disease (CVD) [2-5], chronic kidney disease (CKD) [6,7] and type 2 diabetes mellitus (DM) [8,9], which often co-occur due to overlapping predisposing factors. Existing knowledge show an increased mortality [10-12] and associations between inflammation and cardiovascular comorbidities, CKD and type 2 DM in adults with IJDs [13]. To our knowledge, no previous study has explored the risk of these comorbidities and all-cause mortality in adults with JIA compared to matched comparators.

Objectives: This population-based study assesses comorbidities, autoimmune conditions and all-cause mortality in (1) adults with 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 (≥ 18 years) 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 when registered with the 2 ^nd JIA diagnosis in adulthood. We compared 5-year retrospective comorbidity prevalences and prospective all-cause mortality in (1) adults with JIA versus comparators and (2) adults with JIA with versus without recent DMARD exposure.

Results: Adults with JIA (N = 2932) and comparators (N = 29 097) had similar age (mean age 27.3 years) gender distribution (female gender 70.8%), and centrality index, due to matching. In the adult JIA population, DMARDs had been dispensed or administered during the last year in 52.3%. There was a higher prevalence in adults with JIA than comparators of ischemic heart disease excluding myocardial infarction (JIA vs. comparators (%): 1.0 vs. 0.6), hypertension (3.6 vs. 1.4) and chronic kidney disease (0.5 vs. 0.2), as well as the autoimmune conditions 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) ( table 1 ). Prospective all-cause mortality was higher in JIA than comparators (mortality rate 2.4 vs. 1.8 per 1000 person-years) ( figure 1 ). In adult JIA, neither prevalences of comorbidities and autoimmune conditions, nor all-cause mortality, were affected by recent DMARD exposure.

Conclusions: Focusing on comorbidities and all-cause mortality, this population-based study adds knowledge on long-term outcomes in adult JIA, showing that this patient group has a higher comorbidity burden and all-cause mortality and underscores the need for integrated care throughout adulthood.

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Acknowledgments: NIL.

Disclosure of Interests: Imane Bardan: None declared, Lene Maria Sundbakk: None declared, Joe Sexton: None declared, Tore K. Kvien Grünenthal Pharma, Janssen, Sandoz, AbbVie: board membership, AbbVie, Janssen, Sandoz, UCB Pharma, AbbVie, Galapagos, Novartis, Øyvind Molberg: None declared, Eirik Kristianslund: None declared, Sella Aarrestad Provan: None declared, Anna-Birgitte Aga AbbVie, Eli Lilly, Novartis, Pfizer.