Screening for comorbid autoimmune disease should be considered in children with ANA positive juvenile idiopathic arthritis - results from the south-Swedish juvenile idiopathic arthritis cohort.

Background: There is no consensus or clinical guidelines for screening routines of autoimmune disease in individuals with juvenile idiopathic arthritis (JIA), since results are conflicting whether the risk for such conditions is increased or not among individuals with JIA. The aim of this study was to investigate if the frequency of comorbid autoimmune conditions is increased after JIA diagnosis in a validated population-based JIA cohort in southern Sweden.

Methods: Autoimmune comorbidities were evaluated in a pre-existing population-based JIA cohort of 302 participants, constituting of individuals diagnosed with a validated JIA diagnosis 2000-2010 in southern Sweden. The comorbidities were determined through analysis of diagnosis codes registered after the JIA diagnosis and until 2019. With the use of a reference population of 1510 age- and sex matched individuals, hazard ratios (HR) were calculated with Cox proportional models.

Results: During the study period, 7.7% of the JIA cohort received an autoimmune diagnosis after their JIA diagnosis. Individuals with JIA had an increased risk of autoimmune diseases in general (HR 4.11, 95% CI 2.13-7.91) within the first 7 years of disease, as well as separately for coeliac disease (HR 5.24, 95% CI 1.76-15.65) and hypothyroidism (HR 3.74, 95% CI 1.14-12.30) compared to the reference population. Antinuclear antibody (ANA) positivity was associated with a significantly increased risk of comorbid autoimmune disease in the JIA cohort, with HR 6.21 (95% CI 1.64-23.55) for ANA positive individuals.

Conclusions: Individuals with JIA have a significantly increased risk of being diagnosed with an autoimmune condition after receiving their JIA diagnosis compared to matched references. ANA positivity is associated with a further increased risk. Our results emphasize awareness in physicians of additional autoimmune disorders in individuals with JIA and advocate serological screening of autoimmune conditions during follow-up.