Association of rheumatoid arthritis with allergic diseases: A nationwide population-based cohort study.

BACKGROUND: Low-grade inflammation conditions, e.g., type 2 diabetes, have been shown to be associated with an increased risk of rheumatoid arthritis (RA). However, the association between other chronic inflammatory conditions, e.g., asthma, allergic rhinitis, and atopic dermatitis, is still unclear.
OBJECTIVE: To investigate the risk of RA in patients with allergic diseases, including asthma, allergic rhinitis, and atopic dermatitis, by using a nationwide health claims database.
METHODS: The Taiwan National Health Insurance Research Database was used to assemble a cohort of 170,570 patients ages 20 years old and older diagnosed with allergic diseases, including asthma, allergic rhinitis, or atopic dermatitis. A comparison cohort of 170,238 patients was constructed from the same data base, with frequency matching for sex, 10-year age group, and year of insurance enrollment. Cox proportional hazards regression analyses were conducted to assess the association between the allergic diseases and incident RA.
RESULTS: Asthma (adjusted hazard ratio [AHR] 1.67, [95% confidence interval {CI}], 1.32-2.62) and allergic rhinitis (AHR 1.62 [95% CI, 1.33-1.98]) were significantly associated with the incident RA. These associations remained significant even after excluding patients who had concurrent diagnoses of asthma and allergic rhinitis. Patients with more than one allergic disease had an increased risk of developing RA (AHR 1.98 [95% CI, 1.50-2.62]). Subgroup analysis further indicated that middle-aged and elderly female patients with more than one allergic disease exhibited a high risk of developing RA.
CONCLUSION: Significant associations between common allergic diseases and incident RA was found in this population-based cohort study. Our findings provided support to the hypothesis that allergic diseases and RA might share a similar underlying etiologic pathway related to chronic inflammatory responses.