Bakker PA, et al. - Experts sought to assess the utility of adding structural MRI lesions of the sacroiliitis (SI) joints to the imaging criterion of the Assessment of SpondyloArthritis International Society (ASAS) axial SpA (axSpA) criteria and the utility of replacement of radiographic sacroiliitis by structural MRI lesions in patients with chronic back pain of a short duration. Findings suggested that in most of the patients with early disease onset, no difference in ASAS axSpA classification was noted on assessment of structural lesions (fatty lesions and erosions) with MRI-SI instead of or in addition to conventional radiographs. In the ASAS axSpA classification of patients, structural lesions (fatty lesions and erosions) could be used reliably in the ASAS axSpA classification of patients, as both addition and replacement of radiographs of the SI joints.