COMMENTARY

How Should We Define Sacroiliitis?

Kevin Deane, MD, PhD

Disclosures

April 28, 2016

Associations Between Spondyloarthritis Features and Magnetic Resonance Imaging Findings: A Cross-Sectional Analysis of 1,020 Patients With Persistent Low Back Pain

Arnbak B, Grethe Jurik A, Hørslev-Petersen K, et al
Arthritis Rheumatol. 2016;68:892-900

Study Summary

In this study, Arnbak and colleagues evaluated the relationship between clinical and laboratory features of spondyloarthritis and magnetic resonance (MR) findings of the spine and sacroiliac joints in 1020 patients with persistent low back pain in Denmark who were referred to a spine center.

MR findings for sacroiliitis were defined according to the Assessment of SpondyloArthritis international Society (ASAS), which scores bone marrow edema, fatty marrow deposition, erosions, and sclerosis. Each of these findings was determined to be "present" if there was a minimum of two lesions seen on a single image slice or one lesion seen on two consecutive image slices.

The authors found that 217 of 1020 patients (21%) had sacroiliitis of any type on MR. When broken down by degree of bone marrow edema, 91 of 217 participants (42%) had a "low score" for bone marrow edema, defined as bone marrow edema in <25% of subcortical bone, 58 of 217 (27%) had a medium bone marrow edema score, and 68 of 217 (31%) had a high bone marrow edema score.

Of the clinical and laboratory factors, HLA-B27 positivity and preceding infection were associated with a high bone marrow edema score. A medium score was associated with peripheral arthritis and increasing age but was negatively associated with inflammatory back pain. The only clinical feature associated with a low score was increasing age. Other ASAS clinical features, including elevated C-reactive protein, enthesitis, and inflammatory bowel disease, were not significantly associated with MR sacroiliitis.

The authors concluded that because there were not strong associations between most of the clinical and laboratory features and MR findings, especially with the milder findings of sacroiliitis, the minimum requirements for defining sacroiliitis should be investigated further.

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