POS0038 ANATOMICAL DISTRIBUTION OF MRI LESIONS IN axSpA AND DIFFERENCES BETWEEN PATIENTS WITH AND WITHOUT PERIPHERAL INVOLVEMENT: RESULTS FROM THE ASAS CLASSIFICATION COHORT

Background: Magnetic resonance imaging (MRI) allows the visualization of both inflammatory and structural lesions of the sacroiliac joints (SIJ) and the spine, playing a pivotal role in the diagnosis and classification of axial spondyloarthritis (axSpA). However, there are limited data on the detailed anatomical distribution and variety of MRI lesions in axSpA, particularly among axSpA subgroups, namely between those with and without peripheral involvement. Objectives: To assess the prevalence and anatomical distribution of inflammatory and structural MRI lesions in patients with axSpA, and to compare these lesions between those with pure axial involvement and those with axial plus peripheral involvement. Methods: Data from the Assessment of SpondyloArthritis international Society Classification Cohort (ASAS-CC) were used. Patients with a clinical diagnosis of axSpA at baseline, undergoing SIJ and/or spinal MRI as part of the ASAS-CC study, were included. Peripheral involvement was defined as past or current presence of arthritis, dactylitis or enthesitis. Established ASAS definitions for inflammatory and structural MRI lesions of the SIJ and spine were applied. Investigated lesions are listed in Table 1 and the presence of a lesion was defined based on majority agreement among readers: ≥4/7 readers for SIJ lesions and ≥5/9 readers for spinal lesions. Agreement was based on the exact location at each SIJ quadrant or spinal discovertebral unit level. The frequency and anatomical distribution of inflammatory and structural lesions of the SIJ and spine were evaluated descriptively; axSpA patients with and without peripheral involvement were compared using the Chi-square or Fisher's Exact Test, as appropriate. Results: A total of 199 patients were diagnosed with axSpA at baseline and underwent MRI assessment. SIJ MRI data were available in all these patients (T2-weighted fat-suppressed T2WFS sequences in 199 patients, T1-weighted T1W sequences in 175 patients), while spine MRI data were available in 67 patients (cervical, thoracic and lumbar scans in 42, 40 and 67 patients, respectively, both for T2WFS and T1W sequences). The mean age was 30 years (SD 9.4), with 55% of patients being male. Arthritis, enthesitis, and dactylitis were reported in 49%, 43%, and 6%, respectively, while psoriasis was present in 9% of patients. Subchondral SIJ bone marrow oedema was present in 49% of all patients, with no preference between SIJ quadrants, and there was no significant difference between axSpA subgroups (Table 1). The prevalence of other inflammatory lesions ranged between 4 and 18%, with no significant differences between subgroups (Table 1). Erosions (35%) and fat deposition (22%) were the most frequently observed SIJ structural lesions, also with no significant differences between the subgroups. Erosions and sclerosis were more frequent in the ilium than the sacrum. Spinal bone marrow oedema, fat lesions and syndesmophytes/ankylosis were present in 34%, 19% and 5% of all patients, respectively, and frequencies were similar between subgroups (Table 1). Combined whole spine and SIJ imaging data were available in 40 patients for inflammatory lesions, and in 37 patients for structural lesions. MRI inflammatory lesions were present in both SIJ and spine in 18%, SIJ only in 37%, and spine only in 20% of the patients, with no significant differences between patients with and without peripheral involvement (Table 2). MRI structural lesions were present in both SIJ and spine in 19%, SIJ only in 30%, and spine only in 5% of the patients, with no significant differences between subgroups (Table 2). A sensitivity analysis excluding enthesitis from the definition of peripheral involvement yielded similar results. Conclusion: axSpA patients with and without peripheral involvement exhibit a similar MRI phenotype at the SIJ and spinal level. One-fifth of patients presented with MRI inflammatory lesions of the spine only, without SIJ inflammation, highlighting the importance of spinal MRI imaging in axSpA. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: Bayram Farisogullari: None declared, Stephanie Wichuk: None declared, Xenofon Baraliakos Abbvie, BMS, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Pfizer, Roche and UCB, Abbvie, BMS, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Pfizer, Roche and UCB, Iris Eshed: None declared, Manouk de Hooge UCB, Robert G Lambert: None declared, Mikkel Østergaard AbbVie, BMS, Boehringer Ingelheim, Celgene, Eli Lilly, Galapagos, Gilead, Hospira, Janssen, MEDAC, Merck, Novartis, Novo Nordisk, Orion, Pfizer, Regeneron, Roche, Sandoz, Sanofi, and UCB, AbbVie, BMS, Boehringer Ingelheim, Celgene, Eli Lilly, Galapagos, Gilead, Hospira, Janssen, MEDAC, Merck, Novartis, Novo Nordisk, Orion, Pfizer, Regeneron, Roche, Sandoz, Sanofi, and UCB, AbbVie, Amgen Inc., BMS, Merck, Celgene, and Novartis, Susanne Juhl Pedersen MSD, Pfizer, AbbVie, UCB, Novartis, AbbVie, UCB, Novartis, AbbVie, MSD, Novartis and Nordic Bioscience, Ulrich Weber Novartis, Eli Lilly, Walter P Maksymowych: None declared, Pedro Machado Abbvie, BMS, Celgene, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Orphazyme, Pfizer, Roche and UCB, Abbvie, BMS, Celgene, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Orphazyme, Pfizer, Roche and UCB.