Objective To assess the relationship between a decrease in disease activity score (DAS) and functional ability during 5 years of DAS-steered treatment in recent-onset rheumatoid arthritis (RA) patients, taking into account absolute DAS levels and follow-up duration.
Methods Data from the BeSt study were used, in which treatment was aimed at achieving DAS ≤2.4. The longitudinal relationship between 3-monthly measured DAS and health assessment questionnaire (HAQ) score was assessed using linear mixed modelling during 5 years of treatment, with DAS and HAQ 3 months earlier, change in DAS in last 3 months (delta DAS), time (log-transformed) and their interactions as determinants.
Results Predictors for HAQ were: previous DAS, delta DAS, ln time, the interaction previous DAS×delta DAS, and previous HAQ. The interaction ln time×delta DAS was non-significant, indicating that the association between delta DAS and HAQ was independent of follow-up duration. A decrease from a higher DAS was associated with a smaller HAQ decrease than for a similar decrease from a lower DAS, indicating a non-linear relationship between DAS and HAQ.
Conclusion At any time during 5 years of follow-up, a decrease in DAS was associated with a better functional ability. The magnitude of HAQ improvement depends on the DAS decrease and on the absolute DAS level.
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EvdK and NBK contributed equally to this study.
Funding This study was sponsored by the Dutch College for Health Insurances with additional funding provided by Schering-Plough and Centocor.
Ethics approval This study was conducted with the approval of all participating centres.
Competing interests TWJ, CFA and BACD received speaker fees of less than $US5000 per year from pharmaceutical companies. The authors, not the sponsors, were responsible for the study design, the collection, analyses and interpretation of all data, the writing of this article and the decision to publish.
Provenance and peer review Not commissioned; externally peer reviewed.