Performance of the Assessment in Spondyloarthritis International Society Classification for Axial and Peripheral Spondyloarthritis in an Established Clinical Cohort: Comparison with Criteria Sets of Amor and the European Spondylarthropathy Study Group

Objective.To evaluate the performance of the Assessment in Spondyloarthritis International Society (ASAS) criteria (axial or peripheral) against the Amor and European Spondylarthropathy Study Group criteria in established spondyloarthritis (SpA).Methods.Rheumatologist-diagnosed patients with SpA were retrospectively classified according to the different criteria sets. Clinical characteristics of patients fulfilling all 3 criteria were compared with those who did not, by nonparametric statistics.Results.ASAS classified 90% of the 231 patients, with 169 (73%) fulfilling all 3 criteria sets. Multivariate analysis showed the 62 patients not fulfilling all criteria sets were older at symptom onset (p < 0.001) and less likely to have inflammatory back pain (p < 0.001), peripheral arthritis (p < 0.001), or elevated C-reactive protein levels (p = 0.034).Conclusion.ASAS criteria can be used in established disease.