MRI Lesion Combinations in the Sacroiliac Joint Improve Diagnosis of Axial Spondyloarthritis

Sacroiliac joint
Sacroiliac joint
Researchers investigated the diagnostic utility of different combinations of sacroiliac joint MRI lesions to differentiate axial spondyloarthritis from other conditions.

Assessment of MRI lesion combinations in the sacroiliac joint (SIJ) may improve the ability to differentiate axial spondyloarthritis (axSpA) from other conditions, according to study results published in Rheumatology.

Bone marrow edema of the SIJ is one of the hallmark features used in the classification of axSpA, but it is also associated with other conditions. In this study, the investigators aimed to determine whether the presence of fat lesions in combination with bone marrow edema in the joint space may be useful in the identification of axSpA.

Data from 204 participants (58.8% women; mean age, 33.2 years) were obtained from the Danish prospective cross-sectional MASH study. The study included 41 patients with axSpA, 25 patients with lumbar disc herniation, 46 women with postpartum buttock/pelvic pain, and healthy control groups. Bone marrow edema, fat lesions, and erosion in the SIJ were assessed by MRI, according to the Spondyloarthritis Research Consortium of Canada MRI definitions.

Bone marrow edema adjacent to the joint space was present among all groups, but was observed most frequently in patients with axSpA (63.4%) followed by women with postpartum pain (43.5%). The edema score was highest in patients with axSpA (mean, 5.0) vs all other groups (P <.01 for all).

Bone marrow edema adjacent to fat lesions or erosion were only present in patients with axSpA and women with postpartum pain; however, cutoff scores ≥3 (fat lesions) and ≥4 (erosion) were exclusive to axSpA.

Fat lesions at the joint space were also present in almost all groups, but were observed most frequently in the axSpA group (68%), with the group with healthy men showing the next highest prevalence (10%). Fat lesions at sites of erosion were exclusively observed in patients with axSpA.

Researchers noted that the relatively small size of the axSpA patient group represented a limitation of the study and may have potentially influenced the strength of the results.

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They concluded that bone marrow edema and fat lesions at the SIJ space were frequent in axSpA as well as other conditions, which reduces diagnostic potential. In comparison, fat lesions at sites of erosion, bone marrow edema adjacent to fat lesions, and other factors above certain thresholds were exclusive to axSpA.

“Assessment of lesion combinations may thus improve the diagnostic utility of MRI for differentiating axSpA from other conditions,” they added.


Seven S, Østergaard M, Morsel-Carlsen L, et al. The utility of magnetic resonance imaging lesion combinations in the sacroiliac joints for diagnosing patients with axial spondyloarthritis. A prospective study of 204 participants including post-partum women, patients with disc herniation, cleaning staff, runners and healthy persons [published online April 2, 2020]. Rheumatology (Oxford). doi:10.1093/rheumatology/keaa096