Development and Validation of 3 Preliminary MRI Sacroiliac Joint Composite Structural Damage Scores in a 5-year Longitudinal Axial Spondyloarthritis Study

Objective.In axial spondyloarthritis (axSpA), sacroiliac joint (SIJ) erosion is often followed by fat metaplasia in an erosion cavity (backfill), and subsequently ankylosis. We aimed to combine the Spondyloarthritis Research Consortium of Canada (SPARCC) SIJ structural score for erosion, backfill, and ankylosis into 3 versions of a novel preliminary axSpA magnetic resonance imaging (MRI) SIJ Composite Structural Damage Score (CSDS) and to test these.Methods.Thirty-three patients with axSpA, followed for 5 years after initiation of tumor necrosis factor inhibitor, had MRIs of the SIJs at baseline, and yearly thereafter. Three versions of CSDS were calculated based on different weightings of erosion, backfill, and ankylosis: (1) equal weighting: CSDSequal = (erosion × 0.5) + backfill + ankylosis; (2) advanced stages weighting more: CSDSstepwise = (erosion × 1) + (backfill × 4) + (ankylosis × 6); and (3) advanced stages overruling earlier stages (“hierarchical”) with “<” meaning “overruled by”: CSDShierarchical = (erosion × 1) < (backfill × 4) < (ankylosis × 6).Results.At baseline, all CSDS correlated positively with SPARCC fat and ankylosis scores and modified New York radiography grading, and negatively with the Bath Ankylosing Spondylitis Disease Index and SPARCC SIJ inflammation scores. CSDSstepwise and CSDShierarchical (not CSDSequal) correlated positively with symptom duration and the Bath Ankylosing Spondylitis Metrology Index, and closer with SPARCC ankylosis score and modified New York radiography grading than CSDSequal. The adjusted annual progression rate for CSDSstepwise and CSDShierarchical (not CSDSequal) was higher the first year compared with fourth year (P = 0.04 and P = 0.01). Standardized response mean (baseline to Week 46) was moderate for CSDShierarchical (0.64) and CSDSstepwise (0.59) and small for CSDSequal (0.25).Conclusion.Particularly CSDSstepwise and CSDShierarchical showed construct validity and responsiveness, encouraging further validation in larger clinical trials. The potential clinical implication is assessment of SIJ damage progression by 1 composite score.