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

Patients diagnosed with axSpA with available SIJ MRI and radiograph from five European clinical registries in the EuroSpA Collaboration were included. MRIs were read according to the SPARCC structural score (based on 5 predefined or all slices) and radiographs the rad-mNYc. Cut-offs with 95% specificity for rad-mNYc-positivity for MRI sum scores for individual lesions and for an MRI SIJ hierarchical Composite Structural Damage Score (CSDS5/CSDSall based on erosion, backfill and ankylosis in 5/all slices) and ROC curves were calculated. Internal validation by bootstrapping was performed.

RESULTS

Overall, 640 patients were included; 296 (46%) were rad-mNYc positive. The 95%-specificity cut-off was ≥ 30 for the composite score CSDS5 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

A composite MRI-score based on assessing erosion, backfill and ankylosis for five predefined semicoronal SIJ slices (CSDS5) 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.