Comparison of internal and external responsiveness of the generic Medical Outcome Study Short Form-36 with disease-specific measures in rheumatoid arthritis

OBJECTIVE: To examine the comparative internal and external responsiveness of the generic Medical Outcome Study Short Form-36 Health Survey (SF-36) and disease-specific measures in patients with rheumatoid arthritis (RA). METHODS: Data were collected from 280 RA patients starting anti-tumor necrosis factor treatment. A total of 168 patients completed a questionnaire including the SF-36, the Arthritis Impact Measurement Scales 2 (AIMS2), the Health Assessment Questionnaire (HAQ), a visual analog scale for general health (VAS-GH), and an 11-point numerical rating scale for pain (NRS pain) at baseline and after 12 months. Internal responsiveness was evaluated with paired samples t-tests and standardized response means (SRM). External responsiveness was investigated with receiver-operating characteristic statistics and Spearman rank-order correlation coefficients. A health transition item was used as the external indicator of change. RESULTS: No significant differences in internal and external responsiveness were found between the SF-36 and disease-specific measures within the domains physical function, pain, and psychological function. In the domain social function, the SF-36 was more responsive than the AIMS2. In the domain general health, the SF-36 was less responsive (only internal) than the AIMS2 and VAS-GH. CONCLUSION: Our study showed comparable internal and external responsiveness of the SF-36 compared with disease-specific measures (AIMS2, HAQ, NRS pain) in all health domains, except social function and general health domains. The assumption that disease-specific measures are more responsive to detect intervention-related changes over time is not confirmed by our data.