BACKGROUND: Axial involvement in psoriatic arthritis (axPsA) is associated with more severe disease and increased pain, yet no consensus definition of axPsA exists. This study aims to describe the occurrence and characteristics of MRI and radiographic sacroiliac joint (SIJ) involvement in a European PsA cohort. METHODS: Patients with a clinical diagnosis of PsA or of axial spondyloarthritis with psoriasis and available routine care SIJ MRIs were included from five European registries in the EuroSpA collaboration. SIJ MRIs and radiographs were centrally assessed for inflammatory and structural lesions, differential diagnoses, and globally evaluated for SpA-indicative findings. RESULTS: Among 581 PsA patients (mean age 45 years, 47% male), 31% exhibited SpA-indicative SIJ-MRI findings (MRI-axPsA). In MRI-axPsA patients, the most common lesions were bone marrow edema (BME) (69%), erosions (68%), and fat lesions (58%), generally present bilaterally. BME ≥ 1 cm, inflammation in an erosion cavity, capsulitis, fat lesions ≥ 1 cm, backfill, and ankylosis were observed almost exclusively in MRI-AxPsA patients. Differential diagnoses included osteitis condensans ilii (8%), probable strain-related BME (11%) and degenerative disease (16%). Among 259 patients with radiographs, 29% met the radiographic mNY criteria for ankylosing spondylitis and 38% had SpA-indicative MRI findings. Male sex, HLA-B27 positivity, elevated CRP and history of inflammatory back pain (but not current back pain) were independently associated with MRI-detected axial involvement. CONCLUSION: In this large European cohort, one-third of routine care PsA patients had axial involvement, based on global SIJ MRI assessment. The study supports incorporating MRI into the future definition of axPsA to enable early identification.

Center for Inflammation Research Molecular Immunology and Inflammation Unit VIB Ghent Ghent Belgium

Centre for Rheumatology Research Faculty of Medicine Landspitali University Hospital University of Iceland Reykjavik Iceland

COPECARE Copenhagen Center for Arthritis Research Center for Rheumatology and Spine Diseases Rigshospitalet Glostrup DK 2600 Denmark

DataScience Group Swiss Clinical Quality Management in Rheumatic Diseases Zürich Switzerland

Department of Diagnostic Imaging Sheba Medical Center Tel Hashomer affiliated with School of Medicine Tel Aviv University Tel Aviv Israel

Department of Internal Medicine and Pediatrics Ghent University Ghent USA

Department of Internal Medicine Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark

Department of Radiology and Diagnostic Imaging University of Alberta Edmonton Canada

Department of Radiology Brandenburg Medical School Rüdersdorf bei Berlin Berlin Germany

Department of Radiology Charité Universitätsmedizin Berlin Humboldt Universität zu Berlin Freie Universität Berlin Campus Mitte Berlin Germany

Department of Radiology Copenhagen University Hospital Herlev Gentofte Herlev Denmark

Department of Radiology National Institute of Geriatrics Rheumatology and Rehabilitation Warsaw Poland

Department of Rheumatology and Immunology Inselspital University Hospital Bern Bern Switzerland

Department of Rheumatology University Hospital of Zurich University of Zurich Zurich Switzerland

Department of Rheumatology University Medical Centre Ljubljana Ljubljana Slovenia

Faculty of Medicine University of Ljubljana Ljubljana Slovenia

Institute of Radiology UMC Ljubljana Ljubljana Slovenia

Institute of Rheumatology Department of Rheumatology 1st Faculty of Medicine Charles University Prague Czech Republic

Rheumatology Department Geneva University Hospital Geneva Switzerland

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Navarro-Compán V, et al. Axial spondyloarthritis. Ann Rheum Dis. 2021;80(12):1511–21. PubMed

Rudwaleit M, et al. The assessment of spondyloarthritis international society classification criteria for peripheral spondyloarthritis and for spondyloarthritis in general. Ann Rheum Dis. 2011;70(1):25–31. PubMed

Coates LC et al. GRAPPA treatment recommendations: 2021 update. J Rhuematol, 2022;Jun;49(6 Suppl 1):52-54. doi: 10.3899/jrheum211331.Epub 2022 Mar 15. PMID: 35293339.

Gossec L, et al. EULAR recommendations for the management of psoriatic arthritis with Pharmacological therapies: 2023 update. Ann Rheum Dis. 2024;83(6):706–19. PubMed PMC

Taylor W, et al. Classification criteria for psoriatic arthritis: development of new criteria from a large international study. Arthritis Rheum. 2006;54(8):2665–73. PubMed

Baraliakos X, et al. Secukinumab in patients with psoriatic arthritis and axial manifestations: results from the double-blind, randomised, phase 3 MAXIMISE trial. Ann Rheum Dis. 2021;80(5):582–90. PubMed PMC

Deodhar A, et al. Guselkumab in patients with active psoriatic arthritis who were biologic-naive or had previously received TNFα inhibitor treatment (DISCOVER-1): a double-blind, randomised, placebo-controlled phase 3 trial. Lancet. 2020;395(10230):1115–25. PubMed

Kavanaugh A, et al. Efficacy and safety of ustekinumab in psoriatic arthritis patients with peripheral arthritis and physician-reported spondylitis: post-hoc analyses from two phase III, multicentre, double-blind, placebo-controlled studies (PSUMMIT-1/PSUMMIT-2). Ann Rheum Dis. 2016;75(11):1984–8. PubMed

Alascio L et al. Axial disease in psoriatic arthritis: A challenging domain in clinical practice. Diagnostics (Basel), 2024;14(15).

Poddubnyy D, et al. Axial involvement in psoriatic arthritis cohort (AXIS): the protocol of a joint project of the assessment of spondyloarthritis international society (ASAS) and the group for research and assessment of psoriasis and psoriatic arthritis (GRAPPA). Ther Adv Musculoskelet Dis. 2021;13:1759720x211057975. PubMed PMC

Poddubnyy D, et al. Axial involvement in psoriatic arthritis: an update for rheumatologists. Semin Arthritis Rheum. 2021;51(4):880–7. PubMed

Mease PJ, et al. Influence of axial involvement on clinical characteristics of psoriatic arthritis: analysis from the Corrona psoriatic arthritis/spondyloarthritis registry. J Rheumatol. 2018;45(10):1389–96. PubMed

Aydin SZ, et al. Axial psoriatic arthritis: the impact of underdiagnosed disease on outcomes in real life. Clin Rheumatol. 2018;37(12):3443–8. PubMed

Poddubnyy D. Managing psoriatic arthritis patients presenting with axial symptoms. Drugs. 2023;83(6):497–505. PubMed PMC

Feld J, et al. Axial disease in psoriatic arthritis and ankylosing spondylitis: a critical comparison. Nat Rev Rheumatol. 2018;14(6):363–71. PubMed

Feld J, et al. Axial disease in psoriatic arthritis: the presence and progression of unilateral grade 2 sacroiliitis in a psoriatic arthritis cohort. Semin Arthritis Rheum. 2021;51(2):464–8. PubMed

Gladman DD, et al. Differences in the expression of spondyloarthropathy: a comparison between ankylosing spondylitis and psoriatic arthritis. Clin Invest Med. 1993;16(1):1–7. PubMed

Braga MV, et al. Prevalence of sacroiliitis and acute and structural changes on MRI in patients with psoriatic arthritis. Sci Rep. 2020;10(1):11580. PubMed PMC

Diaz P, et al. Characterising axial psoriatic arthritis: correlation between whole spine MRI abnormalities and clinical, laboratory and radiographic findings. RMD Open. 2022;8(1):e002011. PubMed PMC

Furer V, et al. Prevalence of nonradiographic sacroiliitis in patients with psoriatic arthritis: A Real-life observational study. J Rheumatol. 2021;48(7):1014–21. PubMed

Felbo SK, Terslev L, Østergaard M. Imaging in peripheral and axial psoriatic arthritis: contributions to diagnosis, follow-up, prognosis and knowledge of pathogenesis. Clin Exp Rheumatol. 2018;36(5):24–34. PubMed

Diekhoff T, et al. Comparison of MRI with radiography for detecting structural lesions of the sacroiliac joint using CT as standard of reference: results from the SIMACT study. Ann Rheum Dis. 2017;76(9):1502–8. PubMed

Alle G, et al. Patient profiles in randomized controlled trials versus a Real-World study in psoriatic arthritis: scoping review and metaanalysis. J Rheumatol. 2025;52(2):138–44. PubMed

https://eurospa.eu.

Maksymowych W et al. Validation of SPARCC MRI-RETIC e-tools for increasing scoring proficiency of MRI sacroiliac joint lesions in axial spondyloarth. RMD Open, 2024;10(1).

Hadsbjerg AEF et al. Effect of online training on the reliability of assessing sacroiliac joint radiographs in axial spondyloarthritis: A randomized, controlled study. J Rheumatol, 2024.

Rudwaleit M, et al. The development of assessment of spondyloarthritis international society classification criteria for axial spondyloarthritis (part II): validation and final selection. Ann Rheum Dis. 2009;68(6):777–83. PubMed

Maksymowych WP, et al. MRI lesions in the sacroiliac joints of patients with spondyloarthritis: an update of definitions and validation by the ASAS MRI working group. Ann Rheum Dis. 2019;78(11):1550–8. PubMed

Lambert RG, et al. Defining active sacroiliitis on MRI for classification of axial spondyloarthritis: update by the ASAS MRI working group. Ann Rheum Dis. 2016;75(11):1958–63. PubMed

Linden SVD, Valkenburg HA, Cats A. Evaluation of diagnostic criteria for ankylosing spondylitis. Arthr Rhuem. 1984;27(4):361–8.

Michelena X, et al. Characterising the axial phenotype of psoriatic arthritis: a study comparing axial psoriatic arthritis and ankylosing spondylitis with psoriasis from the REGISPONSER registry. RMD Open. 2022;8(2):e002513. PubMed PMC

Ciurea A et al. Characterisation of patients with axial psoriatic arthritis and patients with axial spondyloarthritis and concomitant psoriasis in the SCQM registry. RMD Open, 2023;9(2).

Regierer AC et al. Comparison of patients with axial PsA and patients with AxSpA and concomitant psoriasis: an analysis of the German register RABBIT-SpA. RMD Open, 2023;9(1).

Williamson L, et al. Clinical assessment of sacroiliitis and HLA-B27 are poor predictors of sacroiliitis diagnosed by magnetic resonance imaging in psoriatic arthritis. Rheumatology (Oxford). 2004;43(1):85–8. PubMed

Poggenborg RP, et al. Head-to-toe whole-body MRI in psoriatic arthritis, axial spondyloarthritis and healthy subjects: first steps towards global inflammation and damage scores of peripheral and axial joints. Rheumatology (Oxford). 2015;54(6):1039–49. PubMed

Diekhoff T, et al. Reporting sacroiliac joint imaging performed for known or suspected axial spondyloarthritis: assessment of spondyloarthritis international society recommendations. Radiology. 2024;311(3):e231786. PubMed

Jadon DR, et al. Axial disease in psoriatic arthritis study: defining the clinical and radiographic phenotype of psoriatic spondyloarthritis. Ann Rheum Dis. 2017;76(4):701–7. PubMed PMC

Queiro R, et al. Psoriatic spondyloarthropathy: a comparative study between HLA-B27 positive and HLA-B27 negative disease. Semin Arthritis Rheum. 2002;31(6):413–8. PubMed

Castillo-Gallego C, et al. Magnetic resonance imaging assessment of axial psoriatic arthritis: extent of disease relates to HLA-B27. Arthritis Rheum. 2013;65(9):2274–8. PubMed

Deodhar A, Gill T, Magrey M. Human leukocyte antigen B27-Negative axial spondyloarthritis: what do we know?? ACR Open Rheumatol. 2023;5(7):333–44. PubMed PMC

Carvalho PD, et al. Axial involvement according to ASAS criteria in an observational psoriatic arthritis cohort. Acta Reumatol Port. 2017;42(2):176–82. PubMed

Chandran V. Psoriatic spondylitis or ankylosing spondylitis with psoriasis: same or different? Curr Opin Rheumatol. 2019;31(4):329–34. PubMed

Queiro R, et al. Clinically asymptomatic axial disease in psoriatic spondyloarthropathy. A retrospective study. Clin Rheumatol. 2002;21(1):10–3. PubMed

Feld J, et al. Is axial psoriatic arthritis distinct from ankylosing spondylitis with and without concomitant psoriasis? Rheumatology (Oxford). 2020;59(6):1340–6. PubMed

Proft F, et al. Early identification of axial psoriatic arthritis among patients with psoriasis: a prospective multicentre study. Ann Rheum Dis. 2022;81(11):1534–40. PubMed PMC

Christiansen AA, et al. Limited reliability of radiographic assessment of sacroiliac joints in patients with suspected early spondyloarthritis. J Rheumatol. 2017;44(1):70–7. PubMed

Maksymowych WP, Østergaard M. What constitutes a positive MRI for clinical trial recruitment of psoriatic arthritis patients with axial involvement?? J Rheumatol. 2022;49(6 Suppl 1):72–4. PubMed

Maksymowych WP, et al. Features of axial spondyloarthritis in two multicenter cohorts of patients with psoriasis, uveitis, and colitis presenting with undiagnosed back pain. Arthritis Rheumatol. 2025;77(1):47–58. PubMed PMC

Baraliakos X, et al. MRI lesions of the spine in patients with axial spondyloarthritis: an update of lesion definitions and validation by the ASAS MRI working group. Ann Rheum Dis. 2022.

Maksymowych WP, et al. Data-driven definitions for active and structural MRI lesions in the sacroiliac joint in spondyloarthritis and their predictive utility. Rheumatology (Oxford). 2021;60(10):4778–89. PubMed

Østergaard M. MRI of the sacroiliac joints: what is and what is not sacroiliitis? Curr Opin Rheumatol, 2020;32(4).

Kwok TSH, et al. Isolated axial disease in psoriatic arthritis and ankylosing spondylitis with psoriasis. Ann Rheum Dis. 2022;81(12):1678–84. PubMed