Prevalence of Co-existing Autoimmune Disease in Rheumatoid Arthritis: A Cross-Sectional Study.

INTRODUCTION: Many autoimmune diseases, including rheumatoid arthritis (RA), share common mechanisms; however, population-based studies of the magnitude of multiple autoimmune diseases in patients with RA have not been performed.

METHODS: We conducted a cross-sectional study using a US administrative healthcare thcare claims database to screen for prevalence of multiple autoimmune diseases in patients with RA and osteoarthritis (OA). Each patient diagnosed with RA between January 1, 2006 and September 30, 2014 was age- and sex-matched with five patients with OA. The prevalence of 37 pre-specified autoimmune diseases during the 24-month period before and after RA or OA diagnosis was compared.

RESULTS: Overall, 286,601 patients with RA and 992,838 matched patients (from 1,421,624 records) with OA were evaluated. During the baseline period, at least one and more than one autoimmune diseases were identified in 24.3% and 6.0% of patients with RA compared with 10.5% and 1.4% of patients with OA, respectively. Highest prevalence rates for patients with RA were for systemic lupus erythematosus (3.8% versus 0.7% for OA) and psoriatic arthritis (3.2% versus 0.4%). Highest odds ratios (ORs) comparing RA with OA were for the prevalence of ankylosing spondylitis (OR 8.0; 95% CI 7.6, 8.5) and psoriatic arthritis (OR 7.8; 95% CI 7.6, 8.1).

CONCLUSION: Patients with RA have more concurrent autoimmune diseases than patients with OA. These data suggest that the interrelationship between RA and other autoimmune diseases, and outcomes associated with the occurrence of multiple autoimmune diseases, may play an important role in disease understanding, management, and treatment decisions.

FUNDING: Bristol-Myers Squibb.