O08 Development and validation of a new tool to assess inflammatory foot disease activity in RA: the Rheumatoid Arthritis Foot Disease Activity Index

Abstract

Abstract Background Rheumatoid arthritis (RA) commonly affects the feet, resulting in pain, walking difficulties, and disability. Omission of foot joints from the disease activity score-28 (DAS-28) may lead to underestimation of foot disease and suboptimal medical and non-medical management. Therefore, the overall objective of this study is to evaluate the measurement properties of the Rheumatoid Arthritis Foot Disease Activity Index-5 (RADAI-F5), a newly developed 5-item (0-10 numerical rating scale) patient-reported outcome measure (PROM) with a summary score (0-10) for measuring foot disease activity in people with RA. Methods Participants with RA recruited from NHS rheumatology outpatient clinics completed the RADAI-F5, a self-modified Rheumatoid Arthritis Disease Activity Index (mRADAI-5) which is a self-reported measure of global disease activity, the Foot function index (FFI), Foot Impact Scale impairment/footwear (FIS-IF) and activity/participation (FIS-AP) subscales. DAS-28 was also recorded for each participant whenever possible. Participants completed RADAI-F5 again at 1 week to allow evaluation of 1-week reproducibility. Construct validity was evaluated using Spearman’s rho to test a priori hypotheses for expected strength of associations between the RADAI-F5 and the alternative disease activity and foot-related disability scales at baseline. Internal consistency was evaluated using Cronbach’s alpha. One-week reproducibility was evaluated using the intraclass correlation coefficient (ICC), 90% smallest detectable change (SDC90), and 95% limits of agreement (LOA). Content validity was evaluated using 5-point Likert scales for readability and relevance. Results Of 142 respondents, 103 were female and 36 were males with a mean (SD) age of 55 years (12.5) and mean (SD) RA disease duration of 39 months (70.4). Mean (SD, range) RADAI-F5 scores for the sample were 5.02 (2.47, 9.2). Associations were largely consistent with a priori hypotheses for construct validity. Strong associations were observed between the RADAI-F5 and MRADAI-5 (0.789, CI 0.73-0.85), the FFI (0.713, CI 0.62-0.79) and FIS-IS (0.695, CI 0.66-0.82) (p < 0.001). Moderate associations were observed with the FFI-AP (0.478, p < 0.001, CI 0.37-0.63). A weak association was observed between the RADAI-F5 and the DAS-28 (0.379, p < 0.001, CI 0.26-0.57). The RADAI-F5 demonstrated high internal consistency (Cronbach’s Alpha=0.82), and floor and ceiling effects were both absent. The RADAI-F5 demonstrated good reproducibility (ICC=0.868, p < 0.001, CI 0.80-0.91) and the value for SDC90 was 2.26. The upper and lower bounds for 95% LOA were -2.57 to 2.80, with 97% of scores observed within these bounds. Content validity was confirmed with 82% and 84% of participants rating the instrument as relevant and easy to understand respectively. The median time for completion was 5 minutes. Conclusion The RADAI-F5 is a highly valid and reliable PROM for measuring foot disease activity in RA patients. Furthermore, the RADAI-F5 appears to be feasible for use in clinical practice and can be used as an adjunct to the DAS28 to measure foot disease activity. Disclosures A. Hoque: Grants/research support; Stipend from Versus Arthritis to complete the Versus Arthritis MSK internship 2019 at Glasgow Caledonian University.