Systemic lupus erythematosus features in rheumatoid arthritis and their effect on overall mortality

Objective. Features of systemic lupus erythematosus (SLE) are commonly observed in patients with rheumatoid arthritis (RA). However, their frequency and clinical significance are uncertain. We examined the frequency of SLE features in RA and their effect on overall mortality. Methods. We assembled a population-based incidence cohort of subjects aged ≥ 18 years first diagnosed with RA [1987 American College of Rheumatology (ACR) criteria] between 1955 and 1995. Information regarding disease characteristics, therapy, comorbidities, and SLE features (1982 ACR criteria) were collected from the complete inpatient and outpatient medical records. Cox regression models were used to estimate the mortality risk associated with lupus features. Results. The study population comprised 603 subjects with incident RA (mean age 58 yrs, 73% women) with a mean followup time of 15 years. By 25 years after RA incidence, ≥ 4 SLE features were observed in 15.5% of the subjects with RA. After adjustment for age and sex, occurrence of ≥ 4 SLE features was associated with increased overall mortality [hazard ratio (HR) 5.54, 95% confidence interval (CI) 3.59-8.53]. With further adjustment for RA characteristics, therapy, and comorbidities, the association weakened but remained statistically significant (HR 2.56, 95% CI 1.60-4.08). After adjustment for age, sex, RA characteristics, therapy, and comorbidities, thrombocytopenia (2.0, 95% CI 1.2, 3.1) and proteinuria (1.8, 95% CI 1.3, 2.6) were significantly associated with mortality. Conclusion. SLE features were common in RA, given sufficient observation time. Subjects with RA who developed ≥ 4 SLE features had an increased risk of death. Proteinuria and thrombocytopenia were individually associated with an increased mortality risk. The Journal of Rheumatology