The impact of area-level socioeconomic status on disease outcomes in rheumatoid arthritis: results from an Australian longitudinal inception cohort study

Objective Socioeconomic status (SES) is associated with differences in health outcomes for individuals with rheumatoid arthritis (RA). We aimed to determine the impact of area-level SES on RA disease activity, disability, quality of life, and biologic/targeted synthetic disease-modifying antirheumatic drug (b/tsDMARD) use in individuals with early RA managed within a protocolised, treat-to-target (T2T), longitudinal observational cohort study. Methods Adult patients with RA diagnosed after June 2003 were included. SES was defined as quintiles of Index of Relative Social Advantage and Disadvantage based on residental address at baseline. Covariates included baseline age, sex, smoking status, body mass index and the Rheumatic Disease Comorbidity Index. Longitudinal multivariable random effects regression models were constructed with restricted cubic splines examining non-linear responses in outcome variables. Biologic/targeted synthetic DMARD use was examined using time-to-event models for recurrent events. Results Of 255 participants, 67% were female with mean age 54 years and 68% had seropositive disease. There was an ordered trend across SES quintiles, such that higher quintiles were associated with lower Disease Activity Score in 28 joints-CRP (p = 0.026), lower modified Health Assessment Questionnaire (p = 0.001) and higher Short-Form-36 Physical Component Score p<0.001). SES quintile was not significantly associated with b/tsDMARD initiation or switching. Conclusion Disadvantageous SES was associated with higher disease activity, disability and poorer quality of life. Our results suggest an inequity in health outcomes for RA patients despite T2T management within a universal healthcare system.