Validation of the ReXSPA (Reductive X-ray Score for Psoriatic Arthritis) index in patients with Psoriatic Arthritis of the RAPSODIA cohort

Abstract

There are many scores available to measure radiographic joint damage in patients with Psoriatic Arthritis (PsA), but most of them were developed for Rheumatoid Arhtritis and then modified for PsA. These scores do not evaluate juxtaarticular bone proliferation. The aim of our study was to validate the Reductive X-Ray Score for Psoriatic Arthritis (ReXSPA), which was recently developed to be used in observational cohorts. Methods: A cross-sectional study was carried out. Consecutive patients ≥18 years old with sA according to CASPAR criteria were included. All patients underwent X-rays of the hands and feet in an anteroposterior view. Two blind readers for the clinical characteristics of the patients and previously trained, scored them by Sharp van der Heijde modified for PsA (PsA-SvdH) and ReXSPA indexes. Time to read and calculate both scores were measured. Results: A total of 66 patients were included, half of them were female, median (m) disease duration of 8 years (IQR: 4-14.3). 132 X-Rays were scored according to PsA-SvdH [m 35 (IQR: 16.3-72.5)] and ReXSPA [m 22 (IQR: 7-46.3)]. Time to read was significantly shorter for ReXSPA than PsA-SvdH [mean 5.8±2.1 vs mean 7.5±2.5 minutes, p<0.0001], as well as, time to calculate them [mean 26.5±14.7 vs mean 55.3±38.3 seconds, p<0.0001]. The correlation between both indexes was excellent (Rho: 0.93). In the multivariate analysis, using both radiographic scores as dependent variable, association of each of the indices with disease duration was observed, and ReXSPA also had association with age. Conclusion: The ReXSPA index has shown validity and a very good correlation with PsA-SvdH. It is quicker to read and to calculate than PsA-SvdH. Subsequent longitudinal evalua-tions will allow demonstrating the validity of these findings.