Evaluation of ASAS Definition for Active Sacroiliitis on Magnetic Resonance Imaging: Correlation with Clinical and Serologic Features of Spondyloarthritis and the Clinical Diagnosis of Axial Spondyloarthritis

Purpose or Learning Objective: To evaluate the relevance of magnetic resonance imaging findings of active sacroiliitis in our institution according to the Assessment of SpondyloArthritis International Society definition in relation to the final diagnosis of spondyloarthritis based on its classification criteria for axial spondyloarthritis.

Methods or Background: The study enrolled 100 patients over a period of 3 years who were evaluated for sacroiliitis with the standard magnetic resonance imaging protocol. Each patient underwent evaluation of Assessment of SpondyloArthritis International Society classification criteria sets. Normal distribution of continuous variables was tested by the Kolmogorov-Smirnov test, and the data were presented as the mean plus or minus the standard deviation. To test differences between the groups, we used a t test for independent groups or the Mann-Whitney test, depending on the normality of distribution. All statistical values were considered significant at P < 0.05. The diagnostic validity of magnetic resonance imaging was assessed using receiver operating characteristic analysis. The correlation analyses were expressed by the Spearman or Pearson correlation coefficient.

Results or Findings: A total of 97% of the patients were referred for magnetic resonance imaging of the sacroiliac joints by a rheumatology specialist, and 50.5% of them met the classification criteria for sacroiliitis. Furthermore, 63.3% of the patients met the imaging arm criteria; 36.7% met the clinical arm criteria. Among the patients with active sacroiliitis confirmed by magnetic resonance imaging-, 76% had a history of inflammatory back pain; 36% were HLA (human leukocyte antigen)-B27 positive. Conversely, 17.9% of the patients with a positive magnetic resonance imaging for active inflammation did not meet inflammatory back pain criteria, and 12.1% of patients with inflammatory back pain exhibited high short tau inversion recovery signal suggestive of sacroiliitis but did not fulfill the magnetic resonance imaging criteria for active inflammation. There was a strong correlation between positive magnetic resonance imaging findings for active sacroiliitis and the final diagnosis of spondyloarthritis based on the classification criteria, with a statistically significant P value (P < 0.0001), a sensitivity of 100%, and a specificity of 78% for an area under the curve of 0.865. A weak positive correlation was observed between inflammatory back pain (P = 0.01) and positive magnetic resonance imaging for sacroiliitis. The correlation with HLA-B27 was very weak.

Conclusion: With appropriate patient selection, considering clinical and serologic features of spondyloarthritis, primarily inflammatory back pain, magnetic resonance imaging is highly reliable to assess active sacroiliitis.

Publication History

Article published online:
02 June 2025