Enthesitis indices identify different patients with this characteristic in axial and peripheral spondyloarthritis and also in psoriatic arthritis: ASAS-PerSpA data

BACKGROUND: In axial spondyloarthritis (axSpA), peripheral SpA (pSpA) and psoriatic arthritis (PsA), enthesitis is a hallmark clinical feature that can be assessed by the SPARCC index, LEI, MASES and MEI. These indices evaluate different locations, which may identify different numbers of patients with enthesitis among SpA subtypes. Thus, the aim of this study was to evaluate whether the proportion of patients with at least one enthesitis across these three most prevalent SpA subtypes differs according to the index used and to evaluate the level of agreement among indices in detecting patients with enthesitis. METHODS: A total of 4185 patients (2719 axSpA, 433 pSpA and 1033 PsA) from the international and cross-sectional ASAS-PerSpA study were included. The proportion of patients with enthesitis identified by the indices was evaluated across the three diseases. Pairwise agreement between indices was computed using Cohen’s kappa. RESULTS: The prevalence rates of patients with at least one enthesitis according to the MEI, MASES, SPARCC index and LEI were 17.2%, 13.5%, 10.7%, and 8.3%, respectively. In axSpA, the indices that identified the most patients with enthesitis were the MEI and MASES (98.7% and 82.4%, respectively); in pSpA and PsA, the indices that identified the most patients with enthesitis were the MEI and SPARCC index (MEI: 100% and SPARCC: 84.6%; MEI: 97.3% and SPARCC: 77%, respectively). In the total population, the MASES vs. MEI showed the strongest agreement (absolute agreement 96.3%; kappa: 0.86); similar results were obtained in axSpA patients (97.3%; 0.90). In pSpA and PsA patients, the SPARCC vs. MEI (97.2%; 0.90 and 95.4%; 0.83, respectively) showed the strongest agreement. CONCLUSIONS: These results suggest that the prevalence of patients with enthesitis across SpA subtypes differs depending on the disease and the index used. The MEI and MASES appeared best for assessing enthesis in SpA and axSpA, while the MEI and SPARCC index appeared best for assessing enthesitis in pSpA and PsA.