Lower Socioeconomic Status is Associated with a More Severe Course of Rheumatoid Arthritis; a 7-year Follow-Up Study.

OBJECTIVES: There is a strong association between low socioeconomic status (SES) and rheumatoid arthritis (RA) outcomes. Yet the association of SES with disease activity and SDFR on the long term, within a contemporary, well-treated cohort and potential mechanisms underlying this association are not fully explored. We therefore investigated long-term disease outcomes in RA and studied SES-related mediators that contribute to the impact of SES on RA severity. METHODS: 789 RA-patients from the Leiden Early Arthritis Clinic were followed for 7 years. SES was defined as educational attainment, categorized as low, intermediate or high. Over time we assessed RA severity using disease activity score-44 (DAS44), the percentage of patients achieving Boolean remission, and the chance of achieving SDFR (sustained absence of synovitis after discontinuing DMARDs ≥1 year). We performed mediation analyses on the association between SES and DAS44 at diagnosis, using patient delay, BMI, smoking and work-related physical strain as potential mediators. RESULTS: At diagnosis and over time, low SES patients compared to high SES patients had higher DAS44 (β=0.37,95%CI:0.18-0.56,p<0.001, β=0.36,95%CI:0.22-0.49,p<0.001), achieved Boolean remission less often (OR=0.52,95%CI:0.37-0.75,p<0.001), yet had a similar chance of achieving SDFR (HR=1.0,95%CI:0.7-1.5,p=non-significant). The higher DAS44 in patients with low SES was not mediated by patient delay, BMI, smoking or work-related physical strain. CONCLUSION: RA-patients with low SES maintained higher DAS44 throughout the disease course and were less likely to achieve Boolean remission. General SES-related factors (patient delay, BMI, smoking and work-related physical strain) did not explain the association with SES, leaving the SES-related causal factor still unknown.