Defining and validating a high specificity MRI cut-off for the radiographic part of the modified New York criteria in patients with axial spondyloarthritis

BACKGROUND: According to the modified New York criteria (mNYc), moderate-severe sacroiliac joint (SIJ) structural damage on radiography is necessary for classifying radiographic axial spondyloarthritis (r-axSpA). In contrast to radiography, MRI provides no ionizing radiation, higher sensitivity for structural damage, better inter-reader reliability, and is gradually replacing radiography. Therefore, we aimed to develop and validate a high specificity MRI cut-off to the radiographic component of the mNYc (rad-mNYc), defined as MRI findings that correspond to an mNY-positive radiograph. METHODS: based on erosion, backfill and ankylosis in 5/all slices) and ROC curves were calculated. Internal validation by bootstrapping was performed. RESULTS: predicting rad-mNYc (specificity 0.95, sensitivity 0.39, area-under-curve 0.83, accuracy with mNYc 69.2%. Internal validation showed moderate accuracy and high positive predictive value. Cut-offs for sclerosis, erosion, backfill and ankylosis were ≥ 9, ≥12, ≥ 5, and ≥ 1, respectively, with sensitivities all ≤ 0.21 except ankylosis 0.34 and accuracy ~ 60%, except ankylosis 67%. Cut-offs using all MRI-slices performed slightly worse or similarly. CONCLUSIONS: ) was the optimal high specificity MRI cut-off to rad-mNYc positivity, being potentially usable in both research and clinical settings, with different thresholds depending on whether sensitivity or specificity is prioritized.