This study identifies baseline predictors of future activity limitation in rheumatoid arthritis (RA). To reinforce the utility of instruments assessing functional ability/activity limitation, we used reference data from healthy referents.
This study includes 189 patients (69% women) with recent-onset RA (onset of joint swelling not more than 12 months at diagnosis) in a prospective cohort ("the Swedish TIRA project") during 27 months from 1996 through 1998. Regular followups were done for a period of 5 years, and 123 healthy persons (50% women) were recruited as referents. Hand function was assessed by the "grip ability test (GAT)" and "signals of functional impairment" (SOFI). Grip force was measured with the electronic device Grippit. Activity limitation was assessed with the Swedish version of the Health Assessment Questionnaire (HAQ).
Throughout the study and for both sexes, GAT, grip force, SOFI-hand, and HAQ were significantly different for the patients compared to healthy referents. In the healthy referents, HAQ was mainly related to age and GAT, whereas in RA HAQ was most obviously linked to grip force. Five years after diagnosis only 8% of HAQ outcome was explained by the baseline measures: HAQ, grip force, SOFI-lower limb, sex, walking speed, and GAT.
Our study provides valuable reference data for several functional ability and activity limitation measures. The HAQ score was explained by different variables in healthy referents compared to patients with RA. Five years after diagnosis only 8% of HAQ outcome was explained by the variables assessed at inclusion.