Comment on the use of self-reporting instruments to assess patients with rheumatoid arthritis: the longitudinal association between the DAS28 and the VAS general health.

Objective: Recently, the use of patient self-reporting instruments instead of clinical, objective measurements to assess rheumatoid arthritis (RA) patients was proposed. This assumes a constant association between disease activity and the self-reporting instruments. The objective was to explore the association (in time) between disease activity and patient perception of general health, disease activity, pain, and functional disability in patients with RA.
Methods: Data of 624 newly diagnosed RA patients who completed 3 years of followup were analyzed. Cross-sectional linear regression models and longitudinal regression models were estimated, with a visual analog scale (VAS) measuring general health (VAS-GH; 0 = best, 100 = worst) as a dependent variable and the Disease Activity Score (DAS28) without the VAS-GH as an independent variable. Other dependent variables were VAS disease activity, pain, and the Health Assessment Questionnaire.
Results: The DAS28 and VAS-GH were significantly associated in RA patients (P < 0.001). However, the explained variance was low (6.7%). From diagnosis to 3 years after the diagnosis, the intercept decreased given the same regression coefficient. The longitudinal regression model showed that the VAS-GH improved during disease course independent of a change in DAS28. Analyses on the other outcome parameters showed similar results.
Conclusion: Patients' perception of health can be different with equal disease activity, depending on the moment in the disease course. Furthermore, our results indicate that self-reported measures on functionality, disease activity, and general health cannot substitute for objective measures of disease activity in RA in longitudinal studies; subsequently, both need to be measured.