Background/Purpose:  There is an unmet need for reliable assessment of structural progression in the sacroiliac joints (SIJ) of patients with axial spondyloarthritis (SpA), but radiography is unreliable and lacks responsiveness. The Spondyloarthritis Research Consortium of Canada (SPARCC) SIJ Structural Score (SSS) is developed and proved to be a new reliable scoring method for evaluating structural lesions based on magnetic resonance imaging (MRI). In this study, we tried to record the features of structural lesions using SSS and to validate SSS in Chinese patients with axial SpA.

Methods:  Three readers (two radiologists and one rheumatologist) investigated fat metaplasia, erosion, backfill and ankylosis seen on MR images from 423 patients. All these patients fulfilled the 2009 ASAS classification criteria for axial SpA. The SSS method for assessment of these four kinds of structural lesions was based on T1-weighted spin echo MRI, and dichotomous scoring (lesion present/absent) of five consecutive slices through the cartilaginous portion of the joint. Scoring ranges were fat metaplasia (0-40), erosion (0-40), backfill (0-20), and ankylosis (0-20).

Results:  There were 342 male and 81 female patients included. The mean age of them was 26.2±8.4 years old. Their symptom duration was 4.7±6.1 years. The total SSS score (sum of four kinds of lesions) of them was 18.4 ± 9.1. 372 (88.0%) were recorded with fat metaplasia, 343 (81.1%) patients were recorded with erosion, 246 (58.2%) were recorded with backfill, and 104 (24.6%) were recorded with backfill. There were no differences of the rates of four kinds of lesions appeared on the left or the right SIJ (all p>0.05). Erosion and backfill were more frequently seen in the upper half than in the lower half SIJ (both p<0.05). The ilium bones were with more often with erosion and fat metaplasia than the sacrum bones (both p<0.05). Interobserver reliability was good for fat metaplasia (ICC 0.70-0.75), also good for erosion (ICC 0.67-0.73), fair to good for backfill (ICC 0.56-0.66), and good to excellent for ankylosis (ICC 0.78-0.88).

Conclusion:  The SPARCC MRI SSS method could detect structural changes in the SIJ with acceptable reliability in Chinese patients with axial SpA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/application-of-the-spondyloarthritis-research-consortium-of-canada-magnetic-resonance-imaging-sacroiliac-joint-structural-score-in-chinese-patients-with-axial-spondyloarthritis/