Inflammation of Sacroiliac Joint in Axial Spondyloarthritis vs Healthy Participants

This article is part of Rheumatology Advisor’s 2017 in-depth coverage of ACR, which took place in San Diego, CA. Our staff will be reporting on the latest treatment advancements and research initiatives for spondyloarthritis. Click here to read more of Rheumatology Advisor‘s conference coverage.

SAN DIEGO — Findings from a study presented at the 2017 American College of Rheumatology (ACR)/Association of Rheumatology Health Professionals (ARHP) Annual Meeting showed that a high percentage of healthy participants with known mechanical strains on the sacroiliac joint (SIJ) had inflammation of the sacroiliac joint shown on magnetic resonance imaging (MRI) scan, according to the ASAS (Assessment of SpondyloArthritis International Society)/OMERACT (Outcome Measures In Rheumatology Clinical Trials) definition. The researchers also characterized inflammation present in healthy participants vs inflammation present in participants with axial spondyloarthritis (axSpA).

“Inflammation shown on MRI of the sacroiliac joint (MRI-SI) is prevalent in axSpA (±30%) but the specificity is not well known,” the researchers wrote. “Hence we compared MRI-SI of healthy individuals and those with known mechanical strain acting upon SIJ.”

For this study, 172 participants had their MRI-SI scored by 3 trained, blinded readers. The 172 participants included 47 healthy participants, 47 age- and gender-matched axSpA patients (with a confirmed positive MRI by central readers) from the SPondyloArthritis Caught Early (SPACE) cohort, 47 age- and gender-matched chronic back pain patients (irrespective of MRI results) from the SPACE cohort, 7 women with postpartum back pain, and 24 frequent runners.

The readers scored the MRIs according to the ASAS/OMERACT and SPARCC (Spondyloarthritis Research Consortium of Canada) definitions, and MRIs were considered positive when at least 2 of the 3 readers agreed. SPARCC scores reported in the study are the mean SPARCC scores from all 3 readers.

The 3 readers agreed 75.6% to 79.9% of the time on the presence or absence of bone marrow edema (BME), (Cohen’s κ 0.48-0.59), and the SPARCC scores correlated well (ICCs 0.824-0.964).

The presence of positive MRI-SI was as follows:

• Healthy volunteers: 11 out of 47 (23.4%)
• Positive axSpA patients: 43 out of 47 (91.5%)
• Patients with chronic back pain: 3 out of 47 (6.4%)
• Patients with postpartum back pain: 4 out of 7 (57.1%)
• Runners: 3 out of 24 (12.5%)

The mean (SD) SPARCC scores were 1.7 (2.4) in healthy participants, 20.9 (13.7) in positive axSpA patients, 0.8 (1.4) in patients with chronic back pain, 4.5 (6.3) in patients with postpartum back pain, and 0.8 (1.1) in frequent runners.

When a SPARCC score ≥2 was used as the cut-off for positivity, the following participants were declared positive:

• Healthy volunteers: 12 out of 47 (25.5%)
• Positive patients with axSpA: 46 out of 47 (97.9%)
• Patients with chronic back pain: 5 out of 47 (10.6%)
• Patients with postpartum back pain: 4 out of 7 (57.1%)
• Runners: 4 out of 24 (16.7%)

When a SPARCC score ≥5 was used as a cut-off for positivity, the following participants were declared positive:

• Healthy volunteers: 4 out of 47 (8.5%)
• Positive patients with axSpA: 41 out of 47 (87.2%)
• Patients with chronic back pain: 1 out of 47 (2.1%)
• Patients with postpartum back pain: 2 out of 7 (28.6%)
• Runners: 0 out of 24 (0%)

“Deep,” or extensive BME-lesions (increase in signal ≥1 cm from the articular surface) were not found in healthy volunteers, patients with chronic back pain, or runners, but were found in 38 out of the 47 positive patients with axSpA (80.9%) and in 1 out of 7 women with postpartum back pain (14.3%).

The researchers concluded that they found the following characteristics of inflammation: a substantial percentage of healthy individuals had a positive MRI-SI according to the ASAS/OMERACT definition; high SPARCC scores (≥5) rarely occurred in healthy individuals, patients with chronic back pain, or runners; and “deep” or extensive lesions seemed to be an exclusive characteristic of sacroiliitis in patients with axSpA.

de Winter J, de Hooge M, van de Sande M, et al. A positive MRI of the sacroiliac joints is not specific for axial spondyloarthritis but frequently occurs in healthy individuals. Presented at: ACR/ARHP 2017 Annual Meeting; November 3-8, 2017; San Diego, California. Abstract 1831.