Multimorbidity burden in rheumatoid arthritis: A population-based cohort study

Objective. To estimate the prevalence and incidence of multimorbidity (MM) in a population-based cohort of patients with rheumatoid arthritis (RA) compared to subjects without RA. Methods. Between 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. Results. The 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). Conclusion. Patients with RA have both a higher prevalence of MM at the time of RA incidence as well as increased incidence thereafter.