To quantify differences and determine the factors contributing to the difference in patient global assessment of rheumatoid arthritis (RA) disease activity (PtGA) between RA patients with multiple morbidities (RA-MM) and those with RA only.
We compared the PtGA between RA-MM patients and those with RA only, followed up in a longitudinal cohort (n = 1,040). In analyses performed on RA-MM patients (n = 575) and those with RA only (matched for swollen joint count, tender joint count, evaluator global assessment, and disease duration), the mean difference in PtGA (ΔPtGA) between the 2 groups was assessed. The contribution of patient characteristics to the explained variation of ΔPtGA in the matched cohort was calculated as semipartial R
RA-MM patients reported higher (or worse) PtGA, with an increased PtGA associated with more morbidities (P for linear trend < 0.01); this relationship remained significant after adjustment for disease activity, age, and disease duration. After matching 294 RA-MM patients to those with RA only, the pairwise comparison of mean PtGA (on a scale of 0-100 mm) was significantly higher (worse) for RA-MM patients (mean ± SD 30.5 ± 24.3) versus those with RA only (25.6 ± 22.9) (mean ΔPtGA 4.9 ± 26.7; P < 0.01 by paired t-test). Variables uniquely contributing to ΔPtGA were fatigue (18%), pain (17%), and modified Health Assessment Questionnaire scores (9%).
In RA patients with multiple morbidities, the perception of RA disease activity as measured by the PtGA might be impacted by the burden of multiple diseases in one individual. RA-MM patients have higher (worse) levels of PtGA scores compared to patients with RA only. The difference in PtGA is mainly explained by differences in fatigue and pain.