Cigarette smoking and risk of undifferentiated peripheral inflammatory arthritis: a propensity score matching analysis.

The present study investigated the association between smoking and undifferentiated peripheral inflammatory arthritis (UPIA) compared with healthy controls. Data were derived from the Connective Tissue Diseases Research Center Undifferentiated Arthritis (CTDRC-UA) cohort, which includes patients older than 16 years with persistent inflammatory arthralgia or arthritis for more than two weeks who do not fulfill classification criteria for any established rheumatic disease. A current smoker was defined as an individual actively smoking at study entry, while past smokers were those who had quit; both groups were categorized as ever smokers. After propensity score matching, 413 UPIA patients were compared with 413 matched controls. The prevalence of ever smoking was similar between UPIA and controls (9.3% vs. 9.4%). Multivariate analysis adjusted for age, sex, marital status, body mass index, and educational level showed no significant association between smoking and UPIA risk (OR 0.81, 95% CI 0.43-1.54, p = 0.523). During a median follow-up of 39 months, patients exhibited three disease trajectories: self-limited disease, progression to another rheumatic disease, or persistent undifferentiated arthritis. Smoking status did not differ significantly across these outcome groups. These findings suggest that smoking is not a universal risk factor for UPIA and does not substantially influence disease outcomes, underscoring the heterogeneity of UPIA and its complex gene-environment interactions. Future prospective studies with detailed exposure assessment should address current limitations-particularly in defining and quantifying smoking exposure-before integrating these results into broader evidence syntheses.