Objective: Comorbidities have been reported to influence physical function, but it is not clear which activities are predominantly impaired, or which other domains of health status are affected in addition to physical function. In this study, we investigated the impact of comorbidities on individual activities of daily living, and other aspects of quality of live in patients with RA.
Methods: In 380 patients with established RA, we quantified comorbidity levels according to the age-adjusted Charlson Comorbidity Index (CCI(A)) and functional disability by serial measures of the HAQ over 1 year. In a subset of 185 patients, we assessed quality of life using Short Form-36 (SF-36). To analyse the relationship between comorbidities, different activities of daily living and health status, we divided patients into four subgroups of CCI(A) and performed analysis of variance (ANOVA) and multivariable general linear regression models adjusted for gender, disease duration and disease activity.
Results: ANOVA showed significant (P < 0.03) increase of disability within each domain of HAQ with increasing level of comorbidity. Similar results were observed using the physical component score (P = 0.003) of the SF-36 and its domains, whereas mental component score (P = 0.31) and its domains were unaffected by comorbidities. In a sub-analysis stratifying patients into different levels of disease activity, we found increase in almost all domains of HAQ within respective groups of CCI(A).
Conclusions: Activities of daily living represented by HAQ are equally affected by comorbidities. More generally, health status was only affected with respect to its physical but not its mental domains.