Epidemiology and risk of juvenile idiopathic arthritis among children with allergic diseases: a nationwide population-based study.

BACKGROUND: Epidemiological research reveals that the incidence of allergic diseases and that of autoimmune diseases have been increasing in parallel, raising an interest in a potential link between the two disorders. However, the relationship between Th2-mediated allergic disease and Th1-mediated juvenile idiopathic arthritis (JIA) remains unclear. This population-based case-control study was aimed at investigating the development of childhood-onset allergic diseases and the subsequent risks of JIA.

METHODS: We included 329 children with JIA diagnosed between 2000 and 2008, and 1316 age- and sex-matched controls. The odds ratios of developing JIA were calculated to determine an association with preexisting allergic diseases.

RESULTS: The incidence rate of JIA in Taiwan between 2000 and 2008 was 1.33 cases per 100,000 children/year according to the International League of Associations for Rheumatology (ILAR) criteria. The children with a single allergic disease had an increased risk of JIA, with adjusted odds ratios of developing JIA of 1.44 for allergic conjunctivitis (95 % confidence interval [CI], 1.07-1.95), 1.50 for allergic rhinitis (1.15-1.96), and 1.44 for asthma (1.00-2.10). The adjusted odds ratios increased with the number of concurrent allergic diseases from 1.50 (95 % CI, 1.12-2.01) for those with only one allergic disease to 1.72 (1.24-2.38) for those with at least two allergic diseases. The adjusted odds ratios of those with at least two allergic diseases increased to 1.84 (95 % CI, 1.19-2.86) for boys and 2.54 (1.42-4.54) for those older than 12 years. The children who made two or more medical visits for associated allergic diseases per year had an increased risk of JIA.

CONCLUSION: Children with onset of allergic diseases were at increased risk of developing JIA. The increased risk was associated with the cumulative effect of concurrent allergic diseases and frequency of seeking medical care. Further study to investigate the role of Th2-mediated allergic diseases that contribute to the development of Th1-mediated JIA is warranted.