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BackgroundPsoriatic arthritis (PsA) can manifest with different musculoskeletal (MSK) features. Ultrasound (US) optimizes the assessment of the different MSK features in PsA. However, there is no consensus on which MSK sonographic lesions and what locations should be evaluated by US.ObjectivesTo examine the prevalence and distribution of key sonographic MSK lesions in patients with PsA.MethodsThis study included two prospectively recruited PsA cohorts. Cohort 1 included 158 consecutive PsA patients and cohort 2 included 94 patients with active PsA prior to initiation of therapy. All underwent a comprehensive US assessment, including both gray scale (GS) and power Doppler (PD) of 50 joints, 40 tendons and 14 entheses. The following sonographic lesions were assessed by two sonographers blinded to clinical data: I. Inflammatory lesions - Synovitis, tenosynovitis, peritenonitis and enthesitis and II. Structural lesions - erosions and bone proliferations. Presence/Absence of these lesions was determined based on previously suggested definitions by OMERACT (when available) or other publication and their prevalence by joint/tendon site was reported.ResultsIn cohort 1, mean ± SD age was 52.7 ± 13 and 55.7% were females. In cohort 2, mean ± SD age was 47.5 ± 13.2 and 48.8% were females. The most prevalent locations of the inflammatory lesions in both cohorts were (Figure 1): Synovitis (small joints) – MCP2 (cohort 1: 11%, cohort 2: 27%), MCP 3 (cohort 1: 7%, cohort 2: 26%), IP1 (cohort 1: 5%, cohort 2: 25%) PIP 3 (cohort 1:3%, cohort 2: 16%), MTP 1 (cohort 1: 31%, cohort 2: 35%), MTP2 (cohort 1: 23%, cohort 2: 30%), MTP3 (cohort 1: 14%, cohort 2: 22%); Synovitis (medium-large joints) – wrist (cohort 1: 27%, cohort 2: 30%) and knee (cohort 1: 13%, cohort 2: 29%); tenosynovitis – 2ndfinger flexors (cohort 1: 2%, cohort 2: 12%) 3rdfinger flexor (cohort 1: 2%, cohort 2: 10%); extensor peritenonitis – MCP2 (cohort 1: 2%, cohort 2: 7%), MCP3 (cohort 1: 4%, cohort 2: 12%), PIP 3 (cohort 1: 3%, cohort 2: 13%), PIP4 (cohort 1: 2%, cohort 2: 12%); enthesitis – lateral epicondyle (cohort 1: 11%, cohort 2: 14%) and triceps (cohort 1: 7%, cohort 2: 20%); erosions – MCP1 (cohort 1: 4%, cohort 2: 5%), MCP2 (cohort 1: 6%, cohort 2: 7%), IP1 (cohort 1: 2%, cohort 2: 2%) PIP2 (cohort 1: 2%, cohort 2: 1%), MTP5 (cohort 2: 4%); bone proliferations – MCP1 (cohort 1: 12%, cohort 2: 7%), MCP2 (cohort 1: 10%, cohort 2: 17%), MCP3 (cohort 1: 5%, cohort 2: 17%), IP1 (cohort 1: 25%, cohort 2: 41%), PIP2 (cohort 1: 10%, cohort 2: 16%), PIP3 (cohort 1: 14%, cohort 2: 26%), DIP2 (cohort 1: 23%, cohort 2: 42%), DIP3 (cohort 1: 18%, cohort 2: 42%) and DIP5 (cohort 1: 29%, cohort 2: 49%).ConclusionThis descriptive study provides comprehensive information on the most commonly affected sites for key inflammatory and structural domains in PsA. This information can inform efforts to develop reduced sonographic score to diagnose or monitor disease activity in PsA.Figure 1.Prevalence and distribution of sonographic inflammatory lesions in PsAREFERENCES:NIL.Acknowledgements:NIL.Disclosure of InterestsNone Declared.