SAT0532 MRI DETECTS SUBCLINICAL PLANTAR FASCIA AND ACHILLES TENDON ENTHESITIS IN PATIENTS WITH PSORIATIC ARTHRITIS, PSORIASIS AND ANKYLOSING SPONDYLITIS

Background Enthesitis is thought to be a key feature driving the development of spondyloarthritis, although head-to-head studies in patients with psoriasis (Pso) versus psoriatic arthritis (PsA) are scarce. In PsA and ankylosing spondylitis (AS) patients the plantar fascia and Achilles tendon are among the entheseal structures most frequently affected clinically. MRI allows for objective detection of enthesitis in patients with rheumatic diseases. Objectives To assess the frequency of MRI-detected enthesitis at the plantar fascia and Achilles tendon in Pso, PsA and AS patients. Methods The cross-sectional observational ‘EXTEND-UP’ study* included patients with Pso (diagnosed by a dermatologist, PsA excluded by rheumatologist), PsA (fulfilling CASPAR criteria) and AS (fulfilling ASAS criteria). With the exception of two PsA patients, no study participants received DMARDs. Study participants were included regardless of the presence/absence of clinically-suspect enthesitis (nail blanching pressure on enthesis). Clinicians were blinded to the MRI-scan results. 3 Tesla MRI-scans of both ankles were performed and evaluated by one observer with over four years of experience in musculoskeletal MRIs, who was blinded to diagnosis and clinical examination. MRI-defined enthesitis was scored following the OMERACT MRI definitions for PsA. Results This study evaluated a total of 79 ankles from 13 Pso patients, 15 PsA patients and 12 AS patients. The MRI-scan of one ankle was not assessable for enthesitis because of suboptimal fat suppression. Overall, MRI-defined enthesitis either at the plantar fascia and/or Achilles tendon was detected in 30% (9/30) of PsA ankles, compared to 8% (2/26) of Pso ankles (p Conclusion This study shows a substantial incidence of MRI-detected plantar fascia and Achilles tendon enthesitis in PsA, occurring more frequently compared to PsO. The clear discrepancy between clinically-suspect enthesitis and MRI-defined enthesitis, even at prototypical sites, warrants caution before using clinical evaluation of enthesitis as part of clinical decision-making or trial outcome measures. Disclosure of Interests Nienke J. Kleinrensink: None declared, Emmerik Leijten: None declared, Wouter Foppen Grant/research support from: WF has received research grants from NovoNordisk and Pfizer. All were paid to the institution. Paid instructor for: WF has received paid instructor fees from Pfizer. All were paid to the institution., Suzanne C. Diepstraten: None declared, Nanette L. Vincken: None declared, Pim de Jong: None declared, Timothy R. Radstake: None declared