SAT0589 Replacing Radiographic Sacroiliitis by Structural Lesions on MRI of the Sacroiliac Joints: Impact on the Classification of Patients According to the Asas Axial SPA Criteria
Authors: P. Bakker, R. van den Berg, Z. Ez-Zaitouni, M. van Lunteren, M. de Hooge, K. Fagerli, M. Turina, M. van Oosterhout, R. Ramonda, T. Huizinga, M. Reijnierse, F. van Gaalen, D. van der Heijde
Journal: Annals of the Rheumatic Diseases (2015)

<h3>Background</h3> Conventional radiography is the most common used method to detect structural lesions in the sacroiliac joints (SIJ) in axial SpondyloArthritis (axSpA). However, reliability is a problem. Besides inflammatory lesions on MRI, which are used to define a positive MRI in the ASAS criteria, structural lesions are visible on MRI. <h3>Objectives</h3> To investigate the impact of replacement of x-rays by structural lesions on MRI on the ASAS axSpA classification of patients. <h3>Methods</h3> Patients in the SPACE cohort (chronic back pain: ≥3 months, ≤2 years, onset &lt;45 years) with (suspicion of) axSpA underwent MRI and X-rays of the SIJs. Three well-calibrated readers, blinded for patient characteristics, read all available baseline MRI-SI (ASAS definition) and X-SI (mod New York). MRI-SI and X-SI were considered positive if 2/3 readers agreed. In addition, MRI T1-weighted images (viewed simultaneously with STIR) were assessed on the presence of structural lesions (in each of the quadrants of each SIJ). Lesions were marked present if 1 lesion was seen on ≥2 consecutive slices. Mean scores of 2 out of 3 agreeing readers (based on ASAS definition) were used. Earlier, we proposed cut-offs to define a positive MRI-SI based on structural lesions (MRI-SI-struct) based on &lt;5% presence among no-SpA patients. These proposed cut-offs are: erosions ≥3, fatty lesions ≥3, fat lesions and/or erosions ≥5. Patients were classified according to the ASAS axSpA-criteria and grouped in the different arms, using the various definitions of MRI-SI-struct instead of X-SI. <h3>Results</h3> For this analysis 294 patients with complete imaging data were included. Using the cut-off for fatty lesions and/or erosions ≥5, classification did not change in 275+3+8 (286) patients (97.3%) (table). In the remaining 8 patients, 5 patients (1.7%) would not be classified axSpA if only MRI-SI-struct was performed, while 3 patients (1.0%) would be additionally classified as axSpA. Furthermore, an additional 8 patients would be classified by different arms. Very similar results were found when replacing X-rays by the definition of a positive MRI-SI-struct for the presence of fatty lesions or erosions alone (both cut-off of &gt;3), and for the scores of the 2 readers individually. <h3>Conclusions</h3> The replacement of x-rays by assessment of structural lesions on MRI does not lead to a different ASAS axSpA classification in the majority of the patients;. These data are promising, however, this is in a cohort of patients with a relatively low number of patients fulfilling the axSpA criteria and in the early phases of the disease. Therefore these data need to be confirmed in patients with established disease. <h3>Disclosure of Interest</h3> None declared