The impact of comorbidities on the physical function in patients with rheumatoid arthritis

Objectives: To investigate the association of comorbidities with mobility limitation and functional disability in patients with rheumatoid arthritis and to identify which comorbidity indicator is the most appropriate to determine this association.

Methods: Sixty rheumatoid arthritis patients were enrolled in a cross-sectional study for a period of 11 months. Comorbidities were assessed using three indicators: (i) the total number of comorbidities; (ii) the Charlson comorbidity index; and (iii) the functional comorbidity index. Disease activity was assessed using the Disease Activity Score 28. Functional capacity was measured using the Health Assessment Questionnaire, and mobility was measured using Timed Up and Go Test and Five-Times-Sit-to-Stand Test. Statistical analysis was performed using a stepwise log-linear multiple regression with a significance level of 5%.

Results: In the final model, only comorbidity was associated with mobility limitation. The functional comorbidity index score explained 19.1% of the variability of the Five-Times-Sit-to-Stand Test (coefficient of determination [R(2)]=0.191) and 19.5% of the Timed Up and Go Test variability (R(2)=0.195). With regard to functional disability, the associated factors were comorbidity and disease activity, which together explained 32.9% of the variability of the Health Assessment Questionnaire score (adjusted R(2)=0.329).

Conclusion: Comorbidities were associated with mobility limitation and functional disability in rheumatoid arthritis patients. The functional comorbidity index proved to be an appropriate comorbidity indicator to determine this association.