OP0237 THE MULTICENTRIC STUDY “DEUS”: DEFINING ENTHESITIS ON ULTRASOUND IN SPONDYLOARTHRITIS
Authors: A. DI Matteo, G. Smerilli, E. Cipolletta, F. Francioso, F. Salaffi, W. Grassi, E. Filippucci
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Enthesitis is the hallmark feature of spondyloarthritis (SpA). Given the inaccuracy of the physical examination, there has been growing interest into the use of imaging, and in particular ultrasound (US), for the evaluation of enthesitis in SpA. The Outcome Measures in Rheumatology (OMERACT) group has recently defined six US elementary lesions of enthesitis in SpA. However, subsequent studies revealed a high prevalence of some of these US lesions in non-inflammatory conditions (i.e., dysmetabolism, fibromyalgia) and healthy subjects, thus questioning the diagnostic power of the OMERACT definitions. Therefore, clarification of the discriminative value of the individual OMERACT US lesions for the detection of SpA-related enthesitis (i.e., differentiation from entheseal involvement occurring in non-inflammatory conditions) is needed. <h3>Objectives:</h3> To assess, in SpA, the diagnostic performance and associations with clinical features of the OMERACT US lesions of enthesitis, and a new US definition of active enthesitis developed by our group ("active enthesitis"). <h3>Methods:</h3> In this multecente study (20 rheumatology centres) SpA patients [psoriatic arthritis (PsA) and axial spondyloarthritis (AS)] and a control group [osteoarthritis (OA) and fibromyalgia (FBM)] were included. The OMERACT US lesions indicating inflammation [entheseal thickening, hypoechoic areas, and power Doppler (PD) signal at the enthesis] and "structural damage" (enthesophytes/calcifications and bone erosions) were considered. As previously described by our group [1], "active enthesitis" was defined as either PD grade ≥1 plus entheseal thickening and/or hypoechogenicity, or PD &gt;1. The patellar insertion of the quadriceps tendon, the patellar and tibial insertion of the patellar tendon, and the calcaneal insertion of the Achilles tendon and plantar fascia were evaluated by physical examination and US. In SpA patients, the associations between the US lesions of enthesitis and the SpA clinical and serological variables of disease activity and severity were explored. <h3>Results:</h3> We included 413 SpA patients (189 PsA, 224 AS) and 282 controls (144 OA, 138 FMB). In the univariate analysis, all the OMERACT US lesions were significantly associated with SpA, except for enthesophytes/calcifications (Figure 1). In the multivariate analysis, only PD at the enthesis (OR=8.77, 95%CI 4.40-19.20, p&lt;0.001) and bone erosions (OR=4.75, 95%CI 2.43-10.10, p&lt;0.001) remained significantly associated with a diagnosis of SpA, after adjustment for age and sex. When "active enthesitis" was considered in the multivariate analysis (entheseal thickening, hypoechoic areas and PD signal at the enthesis were collapsed and removed due to collinearity) this finding (OR=9.20, 95%CI 4.21-23.20, p&lt;0.001) and bone erosions (OR 5.22 2.70-11.0, p&lt;0.001) were significantly associated with SpA. The Achilles tendon was the only enthesis that showed a significant association with SpA (OR=1.93, 95%CI 1.30-2.88, p&lt;0.001) in the multivariate analyses. The following associations between the US lesions of enthesitis and SpA clinical features of disease activity/severity were found in the multivariate analysis: Entheseal thickening: US bone erosions at the enthesis. Hypoechoic areas: ASDAS, LEI, HAQ. PD at the enthesis: US bone erosions at the enthesis and HAQ. Enthesophytes/calcifications: US bone erosions at the enthesis. Bone erosions: none. "Active enthesitis": BASDAI, ASDAS, LEI, CRP, US bone erosions at the enthesis, HAQ. <h3>Conclusion:</h3> This large multicentre study revealed different diagnostic performances of the OMERACT US lesions of enthesitis in SpA patients. PD and bone erosions were the most discriminative US lesions for SpA. The Achilles tendon enthesis was the most informative site. Our newly proposed definition for "active enthesitis" improved specificity and clinical relevance of US enthesitis in SpA. Our data could improve the use of US in the assessment of entheseal involvement in SpA patients <h3>REFERENCES:</h3> [1] Di Matteo A et al. How normal is the enthesis by ultrasound in healthy subjects? Clin Exp Rheumatol 2020;38:472–8. <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> Andrea Di Matteo Janssen, Gianluca Smerilli Novartis, Edoardo Cipolletta: None declared, Francesca Francioso: None declared, Fausto Salaffi: None declared, Walter Grassi Accademia di Medicina, Galapagos, Biopharma, Janssen, UVET, Angelini Ethos, Emilio Filippucci Abbvie, Amgen, BMS, Janssen, Lilly, Novartis, Pfizer, UCB.