Is the Rheumatoid Arthritis Impact of Disease (RAID) score a meaningful instrument for other inflammatory rheumatic diseases? A cross-sectional analysis of data from the German National Database

Objective To analyse the performance of the rheumatoid arthritis impact of disease (RAID) score in patients with ankylosing spondylitis, polymyalgia rheumatica, systemic lupus erythematosus, primary Sjogren's syndrome, idiopathic inflammatory myositis and systemic sclerosis, as compared with rheumatoid arthritis (RA). Methods A total of 12 398 patients from the German National Database were included. For each diagnosis, we calculated age-adjusted/sex-adjusted partial correlation coefficients between RAID and patient global (PtGl) health, PtGl disease activity, physician global (PhGl) disease activity, Well-Being Index (WHO-5) and EuroQoL-5 Dimensions (EQ-5D). As a measure of agreement, the mean differences between the RAID and other outcomes were compared with the respective differences for RA. The effect of each diagnosis on the difference between RAID and the other scores was assessed with linear regression, with RA as the reference. Results Across all diagnoses, RAID correlated strongly with PtGl health (0.71-0.83), moderately to strongly with PtGl disease activity (0.59-0.79), WHO-5 (0.65-0.81) and EQ-5D (0.68-0.73) and weakly with PhGl disease activity (0.23-0.38). Mean differences were calculated for RAID and PtGl disease activity (0 to -0.6), PtGl health (-0.4 to -0.9), WHO-5 (-0.7 to -1.3), EQ-5D (1.1 to 1.7) and PhGl disease activity (1.4 to 2.2). Discrepancies between other scores and RAID were comparable to RA. Linear regression revealed no clinically relevant effect of any of the diagnoses on the difference between RAID and the other outcomes. Conclusion The RAID score performs comparably across all diagnoses investigated. This supports the use of RAID for measuring the impact also of other rheumatic diseases.