POS0297 SACROILIAC JOINT INVOLVEMENT IN PSORIATIC ARTHRITIS – MRI, RADIOGRAPHIC AND CLINICAL FINDINGS IN 581 EUROPEAN ROUTINE CARE PATIENTS

Background:
Axial involvement in psoriatic arthritis (axPsA) is associated with more severe disease and worse pain compared to PsA with isolated peripheral disease. However, a consensus on the definition of axPsA has yet to be reached.
Objectives:
This study aims to describe the occurrence and characteristics of MRI and radiographic sacroiliac joint (SIJ) involvement in a European cohort of patients with PsA.
Methods:
Patients with a clinical diagnosis of PsA (clin-PsA) or axial spondyloarthritis with psoriasis (axSpA+Pso), who had available routine care SIJ MRIs and clinical data, were included from five European registries in the EuroSpA collaboration: Danbio (Denmark), SCQM (Switzerland), ATTRA (Czech Republic), ICEBIO (Iceland), and biorx.sl (Slovenia). SIJ MRIs and radiographs were centrally evaluated by two expert readers for inflammatory and structural lesions, differential diagnoses, and a global assessment of whether the overall appearance of the SIJ MRI was indicative of spondyloarthritis (SpA), i.e., inflammatory axial disease. In case of disagreement, the MRIs were adjudicated by a third reader, an expert musculoskeletal radiologist, member of the Assessment of SpondyloArthritis International Society (ASAS) MRI Group.
Results:
Of the 581 included patients (clin-PsA: n=373; axSpA+Pso: n=208), 47% were male, with a mean age of 45 years. At the time of MRI examination, 76% had not received biologic treatment.
MRI findings in the overall population
In 31% of patients, global assessment of MRI was indicative of SpA (“MRI-axPsA group”), while 69% were assessed as negative for SpA (“MRI-noAxPsA group”). Inflammatory SIJ lesions indicative of axSpA were present in 21% of patients, and structural lesions indicative of axSpA in 28%; 76% of patients had both types of lesions. Common differential diagnoses included osteitis condensans ilii (8%), probable strain-related bone marrow oedema (BME) (11%), and osteoarthritis/degeneration (16%). In 35% of patients, the SIJ MRI was normal, showing neither SpA-related lesions nor differential diagnostic conditions. A total of 259 patients had available radiographs. Of these, 29% met the radiographic component of the modified New York criteria (r-mNYc) for ankylosing spondylitis, while 38% had an MRI indicative of SpA. Radiographic SIJ involvement in patients fulfilling the r-mNYc was predominantly bilateral (90.5%). The MRI-AxPsA patients showed distinct clinical characteristics compared to those without such findings (MRI-NoAxPsA group), as they were younger (mean age 41 years versus 46 years), predominantly male (70% vs. 30%), HLA-B27 positive (55% vs. 27%), and more frequently had nail psoriasis (69% vs. 47%), uveitis (13% vs. 6%), and inflammatory back pain (69% vs. 43%), as well as elevated CRP levels (with a mean (SD) of 13(16) vs.7(12) mg/L). Despite these differences, BASDAI and BASDAI-spinal pain scores were similar across groups, as was the time since diagnosis.
Findings in the subgroup of PsA patients with MRI-detected axial involvement (MRI-axPsA group)
In these patients, MRI findings were predominantly bilateral, with the most common lesions being BME (69%), erosion (68%), and fat lesions (58%). Deep subchondral BME (≥1 cm in depth), inflammation in an erosion cavity, capsulitis, deep fat lesions (≥1 cm in depth), backfill, and ankylosis were observed almost exclusively in this group (Figure 1). Frequencies of sclerosis and BME, but not other MRI findings, were significantly higher in female patients from the MRI-axPsA group, regardless of the clinical diagnosis (clin-PsA vs. axSpA+Pso). Inflammatory lesions, particularly BME, were significantly more frequent in younger MRI-axPsA patients (<35 years: 86%; 35-45 years: 74%; >45 years: 54%; p=0.01), as were erosions (81% vs. 71% vs. 55%, respectively; p=0.01). In contrast, ankylosis was more frequent in older patients >45 years (10% vs. 15% vs. 38%; p=0.01). Among MRI-axPsA patients, age and sex were similar regardless of clinical diagnosis (clin-PsA or axSpA+Pso). However, peripheral arthritis, dactylitis, and nail psoriasis were more frequent in the clin-PsA subgroup, whereas uveitis, enthesitis, inflammatory back pain, and HLA-B27 positivity were more prevalent in the axSpA+Pso subgroup.
Various definitions of axial involvement in PsA
Various clinical, radiographic, and MRI-based definitions of axial involvement in PsA were applied and compared (Table 1), using the overall MRI findings indicative of SpA as the reference (Table 1, 5. MRI ‘global' definition). No clinical or radiographic axPsA definitions performed similarly as this MRI definition.
Conclusion:
In this large European cohort, approximately one-third of routine care patients with PsA had an SIJ MRI indicative of SpA. Among patients with available radiographs, 29% showed radiographic sacroiliitis meeting the r-mNY criteria, of which 38% also had MRI lesions indicative of SpA, i.e., inflammatory axial disease. The findings of this study suggest that clinical and radiographic assessments alone are insufficient for the early identification of axial involvement in routine care of patients with PsA, highlighting the important role of MRI in detecting axial involvement in these patients.