Magnetic Resonance Imaging Compared to Conventional Radiographs for Detection of Chronic Structural Changes in Sacroiliac Joints in Axial Spondyloarthritis

Objective. We investigated the performance of magnetic resonance imaging (MRI) compared to conventional radiographs for detection of chronic structural changes in the sacroiliac joints (SIJ) in patients with axial spondyloarthritis (SpA). Methods. We included 112 patients with definite axial SpA (68 with ankylosing spondylitis and 44 with nonradiographic axial SpA), for whom radiographs and MRI scans of the SIJ performed at the same time were available. Radiographs and MRI of the SIJ were scored for subchondral sclerosis (score 0-2), erosions (score 0-3), and joint space changes (score 0-5) in each SIJ. Readers provided an overall impression of the extent of damage according to the scoring system of the modified New York criteria. Results. In total, 224 SIJ from 112 patients were available for analysis. There was rather low agreement between MRI and radiographs concerning definite erosions of SIJ (kappa = 0.11), moderate agreement for definite subchondral sclerosis (kappa = 0.46) and definite joint space abnormalities (kappa = 0.41), and almost perfect agreement for joint ankylosis (kappa = 0.85). MRI demonstrated a good overall performance in detection of definite "chronic" sacroiliitis, with a sensitivity of 84% and a specificity of 61%. For sacroiliitis fulfilling the modified New York criteria, MRI had a sensitivity of 81% and a specificity of 64% using radiographs as the reference method. Conclusion. MRI demonstrated good overall performance for detection of chronic structural changes in the SIJ as compared to radiographs.