Adults with juvenile idiopathic arthritis carry a heavier comorbidity load

Design

nationwide register-based matched cohort study, 1:10 matching by age, sex and county

Population

2,932 adults with juvenile idiopathic arthritis and 29,097 general population comparators, Norway 2009 to 2024

Primary outcome

five-year comorbidity prevalence and prospective all-cause mortality

Effect

hypertension 3.6% vs 1.4%; type 1 diabetes 1.7% vs 0.7%; mortality 2.4 vs 1.8 per 1,000 person-years

A Norwegian registry study identified adults with at least two specialist contacts carrying a juvenile idiopathic arthritis code between 2009 and 2024, matching each of 2,932 cases to ten population comparators by age, sex and county - 29,097 in all - and comparing five-year comorbidity prevalence and prospective all-cause mortality.

The differences were consistent and mostly cardiometabolic or autoimmune: hypertension 3.6% against 1.4%, ischaemic heart disease excluding myocardial infarction 1.0% against 0.6%, chronic kidney disease 0.5% against 0.2%, type 1 diabetes 1.7% against 0.7%, coeliac disease 1.4% against 0.7%, autoimmune thyroiditis 0.3% against 0.1% and autoimmune alopecia 0.4% against 0.1%. All-cause mortality was 2.4 per 1,000 person-years against 1.8. Within the juvenile arthritis group, recent DMARD exposure made no difference to comorbidity prevalence or to mortality.

The second finding is as useful as the first. The excess is not explained by being on treatment - which is the reassurance patients most often want and the suspicion clinicians most often carry - so it is more plausibly a consequence of the disease, its inflammation and its cumulative glucocorticoid exposure. In practice these are patients who transition out of paediatric care in their late teens and often out of systematic follow-up altogether. Blood pressure, renal function, glucose and a low threshold for a second autoimmune diagnosis belong in the adult review, and somebody has to own it.

• Measure blood pressure and renal function at every adult review in juvenile arthritis, not just joints
• Keep a low threshold for coeliac disease, type 1 diabetes and thyroid disease in this group
• Do not attribute the comorbidity excess to DMARD exposure - it did not differ by treatment
• Name who is responsible for cardiometabolic screening at transition from paediatric care
• Record cumulative glucocorticoid exposure where it is knowable; it plausibly drives part of this

Why it matters

The comorbidity excess did not differ by DMARD exposure, which shifts the explanation from the treatment to the disease.

Don't overread it

Registry-based and retrospective for comorbidity; more frequent specialist contact in the arthritis group inflates detection of any coded diagnosis.

The statistics, in plain English

The absolute differences are small because these conditions are uncommon in young adults - hypertension at 3.6% against 1.4% is a 2.2 percentage point difference, meaning roughly one extra case per 45 patients. The mortality difference, 2.4 against 1.8 per 1,000 person-years, is similarly modest in absolute terms but consistent in direction. Comorbidity here comes from five years of retrospective diagnostic codes, so it partly measures how often these patients see specialists, and patients under rheumatology follow-up get more tests than population comparators.

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