Background/Purpose: Magnetic resonance imaging (MRI) is the gold standard for detection of inflammation and fat metaplasia in the sacroiliac joints (SIJ) and the spine of patients with axial spondyloarthritis (axSpA). Structural changes (erosions, sclerosis and ankylosis) assessed by conventional radiographs (CR) or computed tomography (CT) are characteristic for ankylosing spondylitis (AS). Direct comparisons of these imaging techniques have not been performed to date. In this study we compare the reliability of CR and MRI as compared to CT for detection of structural changes in SIJs of AS patients.

Methods: Complete sets of MRI, CT and CR of SIJs of 69 AS patients and 49 age- and gender-matched controls in whom CTs had been performed for other reasons than back pain were analyzed. Two readers evaluated the images independently and blinded to diagnosis and clinical characteristics in random order. Assessment of lesions was performed based on SIJ-quadrants (SQ). Only definite erosions, sclerosis and ankylosis were recorded, and only SQ changes for which readers agreed on were used for analysis.

Results: The mean age of AS patients was 44.6 years, 72.5% were male, 85.5% were HLA-B27 positive, the mean time since diagnosis was 4.8±5.8 years (range 1 14 years), the mean BASDAI was 4.9±1.8 and the mean CRP was 1.9±2.3mg/dl. In total, 552 SQ (276 pairs) were analyzed. Erosions were found in 131 (23.7%) SQ by CR, 141 (25.5%) by CT and in 167 (30.3%) SQ on T1-MRI. Agreement for erosions was seen for 64 SQ assessed by CR/CT, 100 SQ by CT/MRI and 70 SQ by CR/MRI, with 48.9% of SQ detected by CR also seen on CT and 45.4% detected on CT also seen by CR. The corresponding numbers for CT/MRI were 70.9% and 59.9% and for CR/MRI 53.5% and 41.9%, respectively. Disagreement for erosions was found in 144 (26.1%), 108 (19.6%) and 158 (28.6%) SQ, respectively. Sclerosis was seen in 86 SQ on CR (15.6%), 91 SQ on CT (16.5%) and 63 on T1-MRI (11.4%). Agreement was found in 31 SQ on CR/CT, 22 SQ on CT/MRI and 45 SQ on CR/MRI, with 36.0% SQ detected on CR also seen on CT and 34.1% detected on CT also seen by CR. The corresponding numbers for CT/MRI were 24.2% and 34.9% and for CR/MRI 52.3% and 71.4%. Disagreement for sclerosis was found in 95 (17.2%), 72 (13.0%) and 66 (12.0%) SQ, respectively. Ankylosis was seen in 91 SQ pairs on CR (33,3%), 130 SQ pairs on CT (47,1%) and 106 SQ pairs on MRI (38,4%). Agreement was found in 87 SQ pairs on CR/CT, 94 SQ pairs on CR/MRI and 72 SQ pairs on CT/MRI, with 95.6% SQ detected on CR also seen on CT and 66.9% detected on CT also seen by CR. The corresponding numbers for CT/MRI were 72.3% and 88.7% and for CR/MRI 79.1% and 67.9%. Disagreement for ankylosis was seen in 47 (17.0%), 48 (17.4%) and 53 (19.2%) SQ pairs, respectively. In controls, 392 SQ were analyzed. Erosions were found in only 19 (4.8%) SQ and sclerosis in 23 (5.9%) SQ, while no patient showed ankylosis.

Conclusion: Erosions and ankylosis are more common than sclerosis in SIJs of AS patients and rarely seen in controls. The agreement between methods was rather limited. Compared to CT, less erosions were detected by MRI and CR when only erosions agreed on were counted. CT and MRI were more reliable than CR for the detection of ankylosis. The superiority of MRI to detect erosions may be related to early disease stages, while erosions seen on CT seem to be due to detection in later stages of AS.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/which-is-the-most-reliable-imaging-method-for-detection-of-structural-changes-in-the-sacroiliac-joints-of-patients-with-ankylosing-spondylitis-a-cross-sectional-study-comparing-mri-ct-and-convention/