Sacroiliac damage on MRI in axial spondyloarthritis and chronic back pain, women with postpartum back pain, runners and healthy subjects

Objective To investigate the extent and performance of structural lesions in sacroiliac joints on MRI (MRI-SI) in patients with axial spondyloarthritis (axSpA), chronic back pain, postpartum back pain, runners and healthy subjects. Methods MRI-SIs in 172 subjects, including 47 patients with diagnosed axSpA fulfilling the Assessment of SpondyloArthritis international Society (ASAS) criteria, 47 patients with chronic back pain, 7 women with postpartum back pain, 24 runners and 47 healthy individuals, were scored by two well-trained readers for erosions, fatty lesions, sclerosis and ankylosis, using an adjusted Spondyloarthritis Research Consortium of Canada scoring method. In addition, cut-off values proposed by the Imaging workgroups of Leiden and the ASAS were tested. Results Of the axSpA patients, 37 (79%) had structural lesions. Most frequently reported structural lesions were erosions in 35 (75%) patients and fatty lesions in 19 (40%) patients. Erosions and fatty lesions were uncommon in chronic back pain, runners and healthy individuals. There was a statistically significant difference in the prevalence of erosions, fatty lesions and ankylosis between axSpA and chronic back pain. Ankylosis was rare in both groups. Comparing axSpA to non-axSpA, Leiden cut-off definitions were more specific than ASAS cut-offs. Conclusions Structural changes resembling axSpA may occur in individuals who do not have axSpA, but at a lower rate than inflammatory changes. Erosions and fatty lesions are most specific. Using cut-off definitions for these structural lesions results in good discrimination between axSpA and non-axSpA. In axSpA, structural lesions primarily occur in concordance with ongoing inflammation.