POS0635 RELIABILITY OF ELEMENTARY ULTRASONOGRAPHIC LESIONS IN PSORIATIC ARTHRITIS AND DEVELOPMENT OF AN ATLAS: RESULTS OF THE ECHO-APACHE STUDY

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Background: Synovitis, tenosynovitis, enthesitis, and dactylitis are key lesions in psoriatic arthritis (PsA). Ultrasound is useful for evaluating them, but its role for diagnosis and follow-up is still unclear. Objectives: To assess the intra- and inter-reader reliability of the classic elementary lesions in PsA (synovitis, tenosynovitis, enthesitis) and dactylitis according to OMERACT definitions among expert sonographers participating in the APACHE cohort. 2. To assess the usefulness of a training in images interpretation. 3. To establish an ultrasound atlas of typical lesions in PsA. Methods: APACHE is a French multicentre prospective cohort of very early peripheral PsA (<1 year) followed in a standardized manner for 10 years (Clinical trial.gov NCT03768271). An ancillary ECHO-APACHE study was conducted to analyze the reliability of ultrasound lesions in PsA. The data analyzed consisted of images of synovitis, tenosynovitis, enthesitis, and dactylitis from patients with confirmed PsA, collected from 26 rheumatology centers in France in 2020. Ultrasound images were centralized, and high-quality images were selected by 4 experts. The image readings were performed to evaluate the elementary lesions of PsA according to OMERACT. Dactylitis was defined by soft tissue edema or thickening and an elementary lesion among synovitis, tenosynovitis, enthesitis and paratendinitis. For step 1, in each participating center (N=26), one expert sonographer scored two times a set of images, and intra- and inter reliability (compared to a reference sonographer) were assessed. For step 2, a videoconference training session, with the implementation of new images by the centers and the inclusion of 4 new centers, was followed by a new phase of reproducibility evaluation between 2 sonographers blinded to each other in each center: one experienced sonographer and one less experienced sonographer (Co-APACHE). Step 3 included new training focused exclusively on images of dactylitis with 25 expert sonographers and 19 Co-APACHE, and a third exercise with images of dactylitis was proposed. Intra- and inter-reader reliability were assessed using the Light Kappa coefficient based on an average of Cohen's kappas. Results: 29 centers participated between 2020 and 2024. In step 1, 51 images out of 160 were selected by the experts (10 synovitis, 13 enthesitis, 14 tenosynovitis, 14 dactylitis). In step 2, 91 images out of 178 were selected (19 synovitis, 20 enthesitis, 22 tenosynovitis, and 30 dactylitis). In step 3, 32 images of dactylitis were evaluated. Before training, intra-reader reliability was good for synovitis, tenosynovitis and enthesitis lesions, and inter-reader reliability was moderate, or even poor for dactylitis (Table 1). Reliability in step 2 improved after videoconference training for all items except dactylitis (Table 1). The results of step 3 were moderate to good (Table 1). The project enabled the production of an atlas of typical ultrasound images of PsA. Conclusion: Training is an essential prerequisite to achieve good intra- and inter-reader reliability in the assessment of ultrasound lesions of PsA, particularly dactylitis. The creation of an ultrasound atlas is a valuable tool for the diagnosis and ultrasound monitoring of PsA. REFERENCES: NIL . Table 1Intra- and inter-reader reliability of elementary lesions in PsA. Red: kappa ≤0.4 (Poor); Orange: kappa 0.4-0.6 (Moderate); Green: kappa >0.6 (Good/Excellent).SonographerStep 1Step 2Step 3Intra-readerInter-readerIntra-readerInter-readerIntra-readerInter-readerSynovitisB mode SynovitisReferent0.50[0.38-0.65]0.32[0.15-0.56]0.81[0.68-0.89]0.72[0.54-0.84]Co-Apache0.80[0.67-0.90]0.69[0.53-0.82]PD SynovitisReferent0.80[0.59-0.9]0.70[0.33-0.92]0.90[0.85-0.95]0.84[0.74-0.92]Co-Apache0.87[0.81-0.93]0.79[0.69-0.89]TenosynovitisB mode TenosynovitisReferent0.63[0.50-0.70]0.49[0.33-0.68]0.66[0.54-0.75]0.55[0.42-0.67]Co-Apache0.72[0.64-0.8]0.65[0.55-0.74]PD TenosynovitisReferent0.51[0.39-0.62]0.40[0.26-0.55]0.83[0.61-0.93]0.76[0.51-0.89]Co-Apache0.82[0.65-0.92]0.77[0.60-0.90]EnthesitisB mode EnthesitisReferent0.73[0.64-0.82]0.60[0.43-0.78]0.61[0.14-0.74]0.37[0.00-0.58]Co-Apache0.47[0.06-0.66]0.42[0.00-0.65]PD EnthesitisReferent0.62[0.54-0.74]0.47[0.28-0.72]0.81[0.73-0.90]0.59[0.44-0.75]Co-Apache0.76[0.63-0.87]0.59[0.43-0.74]DactylitisSoft tissue edema or thickening (B mode)Referent0.36[0.26-0.50]0.19[0.05-0.30]0.40[0.34-0.49]0.12[0.08-0.18]Co-Apache0.33[0.23-0.44]0.21[0.15-0.29]Soft tissue (PD)Referent0.41[0.32-0.55]0.22[0.13-0.36]0.49[0.36-0.66]0.27[0.13-0.44]Co-Apache0.46[0.32-0.61]0.35[0.21-0.57]B mode SynovitisReferent0.27[0.13-0.46]0.19[0.07-0.35]0.48[0.31-0.63]0.30[0.17-0.46]0.69[0.61-0.77]0.52[0.30-0.71]Co-Apache0.57[0.44-0.71]0.36[0.18-0.50]0.68[0.55-0.79]0.46[0.34-0.66]PD SynovitisReferent0.47[0.33-0.62]0.24[0.13-0.49]0.37[0.25-0.45]0.22[0.14-0.35]Co-Apache0.58[0.49-0.78]0.33[0.22-0.44]B mode TenosynovitisReferent0.36[0.22-0.53]0.19[0.08-0.33]0.33 [NA]0.00 [NA]0.80[0.71-0.87]0.68[0.00-0.85]Co-Apache0.00 [NA]-0.01 [NA]0.74[0.49-0.82]0.63[0.20-0.80]PD TenosynovitisReferent0.31[0.22-0.42]0.13[0.06-0.23]Co-ApacheB mode EnthesitisReferent0.17[0.08-0.33]0.04[0.00-0.10]0.47[0.39-0.54]0.25[0.18-0.35]0.80[0.71-0.85]0.67[0.25-0.68]Co-Apache0.45[0.36-0.54]0.27[0.18-0.40]0.70[0.61-0.79]0.58[0.25-0.65]PD EnthesitisReferent0.40[0.28-0.62]0.07[0.01-0.19]0.37[0.25-0.49]0.24[0.16-0.35]Co-Apache0.40[0.27-0.48]0.22[0.14-0.31]B mode ParatendinitisReferent0.70[0.60-0.78]0.57[0.03-0.57]Co-Apache0.61[0.51-0.70]0.42[0.02-0.50] Acknowledgements: NIL . Disclosure of Interests: None declared . © The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.

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