Background/Purpose: Multimorbidity is associated with increased risk of adverse outcomes in patients with rheumatoid arthritis (RA). Multiple studies have suggested increased burden of multimorbidity in patients with RA, but the extent of this increase and whether this excess in multimorbidity changes over time has not been well characterized.

Methods: In this retrospective, population-based cohort study, residents of a geographically well-defined area who met 1987 ACR criteria for incident RA in 1999-2013 were identified from a comprehensive medical record linkage system.  Age and sex-matched non-RA comparators were selected from the same underlying population. Index date for each non-RA comparator corresponded to an incidence date of a matching patient with RA. Their medical records were then reviewed for 25 chronic comorbidities from a combination of the Charlson Comorbidity Index, Elixhauser Comorbidity Index, and Rheumatic Disease Comorbidity Index at index date and after index date. Rheumatic comorbidities were not included. Aalen-Johansen methods were used to estimate the cumulative incidence of multimorbidity (presence of 2 or more chronic comorbidities) or severe multimorbidity (5 or more) adjusted for the competing risk of death. Cox proportional hazards models with adjustment for age, sex, obesity (body mass index ≥30 kg/m²) at index date, and calendar year were used to compare the rate of development of multimorbidity or severe multimorbidity between the RA and non-RA cohorts.

Results: A total of 597 patients with incident RA (70% female; 90% Caucasian, 3% African-American; mean age 55.5 years) and 594 non-RA (70% female; 91% Caucasian, 3% African-American; mean age 55.4 years) were studied. By incidence/index date, RA patients had an increased prevalence of multimorbidity compared to non-RA subjects (38% RA vs. 32% non-RA, p=0.021) while prevalence of severe multimorbidity was similar (5% RA vs. 4% non-RA, p=0.68). The mean number of comorbidities (excluding rheumatic) by index date were 1.4 in RA patients and 1.2 in non-RA subjects. During follow-up (median 10.2 years RA patients, 10.3 years non-RA), RA subjects also showed an increased incidence of multimorbidity (214 RA vs. 188 non-RA; adjusted hazard ratio (HR): 1.41; 95% confidence interval (CI): 1.16–1.72). By 10 years after RA incidence/index, the cumulative incidence of multimorbidity among those without multimorbidity at index was 56% among the RA patients (95% CI: 51-62%) compared with 48% among the non-RA (95% CI: 43-54%; see figure). RA patients showed some increase in incidence of severe multimorbidity (167 RA vs. 139 non-RA; adjusted HR: 1.21; 95%CI: 0.96-1.51).

Conclusion: Patients with RA have both a higher prevalence of multimorbidity by the time of RA incidence as well as increased incidence thereafter. Studies investigating the underpinnings and implications of these findings are underway.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/prevalent-and-incident-multimorbidity-in-rheumatoid-arthritis-a-population-based-cohort-study/