The responsiveness of health status measures in patients with rheumatoid arthritis: Comparison of disease-specific and generic instruments

Objective. To compare the responsiveness of 2 disease-specific questionnaires, the Modified Health Assessment Questionnaire (MHAQ) and the Arthritis impact Measurement Scale (AIMS') with corresponding dimensions (physical function, mental health, pain, and fatigue) in a generic health status measure [the MOS Short Form-36 (SF-36)] in patients with rheumatoid arthritis (RA). Methods. Within the framework of an observational study, a prospective cohort of 595 patients with RA from a community based patient register responded to a questionnaire at baseline and after 2 years' followup. Changes in patient global disease activity assessed on a categorical verbal rating scale (range 1-5) were used as external indicator of improvement or deterioration. Responsiveness was evaluated with standardized response means (SRM), calculated as mean change score divided by the standard deviation of the mean change score. Results. Changes in patient global disease activity were classified as much better (n = 33), slightly better (n = 108), no change (n = 291), slightly worse (n = 108), and much worse (n = 20). There were no significant differences in responsiveness between SF-36 and the disease-specific measures within the same dimensions of health. The SRM of the tools within the dimension of pain (AIMS2 and SF-36) were moderate (0.5-0.8) to large (> 0.8) consistently in both directions (improvement and deterioration). The physical function subscales detected the same pattern, but the magnitude of the gradients was smaller. The fatigue and mental health subscales did not show any clear and consistent pattern of change. Conclusion. In patients with RA, there was no difference in responsiveness of subscales from SF-36 and disease-specific instruments when using changes in patient assessed global disease activity as an external indicator of change in health status. The dimension of pain was most sensitive to changes in patient assessed global disease activity followed by physical function, fatigue, and mental health.