The Rheumatoid Arthritis Foot Disease Activity Index-5 (RADAI-F5) is a valid and reliable tool for the assessment of foot disease activity in patients with rheumatoid arthritis (RA), according to a study published in Arthritis Care and Research.

Currently, there is no widely used, validated and clinically feasible method for the assessment of foot disease activity in RA. Accordingly, study investigators developed and aimed to validate a new concise measure of foot disease activity.

In total, 142 patients with RA (72.5% female) completed the RADAI-F5, a self-administered 5-item patient reported outcome measure that assessed global disease activity in the foot. Additionally, patients also self-completed the Foot Function Index (FFI), 28 joint count Disease Activity Score (DAS28-ESR), as well as the Foot Impact Scale impairment/footwear (FIS-IF) and activity/participation (FIS-AP) restriction subscales. The RADAI-F5 was completed at baseline as well as 1 week and 6 months from baseline. Over the 6-month period, the psychometric properties of the assessments were examined in terms of construct validity, content validity, and longitudinal validity, internal consistency, 1-week reproducibility, and responsiveness.

Patients in the study presented with a mean age of 55 years and a median RA disease duration of 10 months. The investigators found strong positive correlations for the mRADAI-5 (rs = 0.789; 95% CI, 0.73-0.85; P <.001), FFI (rs = 0.713; 95% CI, 0.62-0.79; P <.001) and FIS-IF (rs = 0.695; 95% CI, 0.66-0.82; P <.001). These findings, according to the researchers, confirmed construct validity. In terms of construct validity, there were also moderate positive correlations with the FIS-IF (rs = 0.69; 95% CI 0.66-0.82; P ≤.001) and FIS-AP (rs = 0.48; 95% CI, 0.37-0.63; P <.001) subscales.


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In addition, the RADAI-F5 had high internal consistency (Cronbach’s Alpha=0.90) and very good reproducibility at week 1 (ICC=0.868; 95% CI, 0.80-0.91; P ≤.001; smallest detectable change=2.69). Approximately 82% of respondents said the instrument was relevant and easy to understand, further confirming content validity of the RADAI-F5.

A limitation of this retrospective study was the lack of standardized medical care across all participants, which may limit the ability to infer direct benefits of the RADAI-F5 with specific therapeutic regimens for RA.

RADAI-F5 “is recommended for use by rheumatologists and/or rheumatology nurse specialists alongside composite global disease activity indices and Allied Health Professionals such as podiatrists and physiotherapists involved in delivering non-medical foot care in RA,” wrote the investigators.

Reference

Hoque A, Gallagher K, McEntegart A, et al. Measuring inflammatory foot disease in rheumatoid arthritis: development and validation of the Rheumatoid Arthritis Foot Disease Activity Index-5 [published online May 20, 2020]. Arthritis Care Res (Hoboken). doi: 10.1002/acr.24259