What do we measure with 28-joint DAS in elderly patients? An explorative analysis in the NOR-DMARD study

OBJECTIVE: Insight into the influence of ageing on disease outcomes is limited. The objective of this study was to examine the potential effect of age on disease activity using the 28-joint DAS (DAS28) and its components in patients with RA. METHODS: Baseline data of DMARD-naïve patients with RA from the Norwegian Register of DMARDs were used. Linear regression explored the strength of the association between age (<45, 45–65 and >65 years) and each DAS28 component while accounting for education and gender. Adjusted predicted scores for DAS28 components and total DAS28 score were calculated for each age category. RESULTS: Baseline data from 2037 patients [mean age 55.2 years (s.d. 14.0), 68% females] were available. Regression models had to be stratified for gender (P for interaction <0.001); education was a significant covariate. Males >65 years of age with an intermediate level of education have a 56% higher ESR and 25% higher 28-joint swollen joint count as compared with their younger counterparts (<45 years). For females, corresponding differences were 51% and 27%, respectively. The age effect on the 28-joint tender joint count and patient global assessment was negligible. In patients with an intermediate education level, DAS28 was 5.0 vs 5.5 (10% increase) in the youngest vs oldest age groups, independent of gender. CONCLUSION: The age-related increase in ESR and 28-joint swollen joint count scores without a relevant corresponding increase in 28-joint tender joint count and patient global assessment might imply that age-related processes (e.g. soft tissue changes, physiological ESR increase) contribute to a higher DAS28 in elderly patients.