Multimorbidity Burden in Rheumatoid Arthritis: A Population-based Cohort Study

Abstract

ObjectiveTo estimate the prevalence and incidence of multimorbidity (MM) in a population-based cohort of patients with rheumatoid arthritis (RA) compared to subjects without RA.MethodsBetween 1999–2013, residents of Olmsted County, Minnesota with incident RA who met the 1987 American College of Rheumatology criteria were compared to age- and sex-matched non-RA subjects from the same population. Twenty-five chronic comorbidities from a combination of the Charlson, Elixhauser, and Rheumatic Disease Comorbidity Indices were included, excluding rheumatic comorbidities. The Aalen-Johansen method was used to estimate the cumulative incidence of MM (MM2+; ≥ 2 chronic comorbidities) or substantial MM (MM5+; ≥ 5), adjusting for the competing risk of death.ResultsThe study included 597 patients with RA and 594 non-RA subjects (70% female, 90% White, mean age 55.5 yrs). At incidence/index date, the prevalence of MM2+ was higher in RA than non-RA subjects (38% RA vs 32% non-RA, P = 0.02), whereas prevalence of MM5+ was similar (5% RA vs. 4% non-RA, P = 0.68). During follow-up (median 11.6 yrs RA, 11.3 yrs non-RA), more patients with RA developed MM2+ (214 RA vs 188 non-RA; adjusted HR 1.39, 95% CI 1.14–1.69). By 10 years after RA incidence/index, the cumulative incidence of MM2+ was 56.5% among the patients with RA (95% CI 56.5–62.3%) compared with 47.9% among the non-RA (95% CI 42.8–53.7%). Patients with RA showed no evidence of increase in incidence of MM5+ (adjusted HR 1.17, 95% CI 0.93–1.47).ConclusionPatients with RA have both a higher prevalence of MM at the time of RA incidence as well as increased incidence thereafter.