Objective: To determine the most relevant radiological features in quantitative magnetic resonance imaging (MRI) of sacroiliac (SI) joints in patients with recent-onset ankylosing spondylitis (AS) versus patients with SI involvement due to other rheumatic diseases, or to degenerative SI pain.
Methods: We retrospectively analyzed laboratory values, clinical data, and MRI of the SI joints of 179 patients admitted for evaluation of AS-suspicious SI pain. Standardized MRI sequences were performed at time of first presentation, then archived, and retrospectively quantitatively assessed using a modified SPARCC method for formal statistical comparisons.
Results: Of all patients, 27 (15%) were diagnosed with definite AS. The remainder had SI involvement in other rheumatic diseases, HLA-B27- spondyloarthropathy, or nonspecific degenerative changes. While joint space irregularities, bone marrow edema, subcortical cysts, and contrast medium enhancement were found in MRI of all patients, these features were inconsistent, and only erosions were statistically significantly (p < 0.02) in patients diagnosed with AS. Only in AS, the presence of erosions and the quantitative SPARCC erosion subscore correlated to a statistically significant degree (p < 0.02) with laboratory levels of inflammation.
Conclusion: Erosions alone, not bone marrow edema or contrast medium enhancement, are the most disease-specific measurable imaging findings in SI MRI of patients with AS.