Defining the Minimally Important Change for the SpondyloArthritis Research Consortium of Canada Spine and Sacroiliac Joint Magnetic Resonance Imaging Indices for Ankylosing Spondylitis

Abstract

Objective.: To define the minimally important change (MIC) in the SpondyloArthritis Research Consortium of Canada (SPARCC) spine and sacroiliac (SI) joint magnetic resonance imaging (MRI) indices in patients with ankylosing spondylitis.Methods.: MRI scans were performed during a placebo-controlled trial of adalimumab (no. NCT00195819). Two independent readers, blinded to treatment and sequence, determined SPARCC scores for the spine and SI joints and a global evaluation of change (GEC; “much worse,” “worse,” “no change,” “better,” or “much better”; categories other than “no change” were pooled together as “change”) between baseline–Week 12, baseline–Week 52, and Weeks 12–52. Mean absolute changes in SPARCC scores (95% CI) were calculated for each interval, treatment group, and GEC. Receiver-operating characteristic (ROC) curves were used to identify the MIC. Relationships of MIC to clinical responses were examined.Results.: Reader agreement on GEC evaluations was > 70%. Changes in SPARCC scores were generally comparable between time intervals and treatment groups for “change” and “no change” categories and were combined for each category; change in score was significantly associated with GEC of “change” (area under ROC curves: spine 0.839; SI joints 0.960). ROC curves peaked at values of 5.0 for the spine and 2.5 for SI joints. Placebo-treated patients achieving > 2.5 unit improvement in SI joint score had significantly better clinical responses than placebo-treated patients who did not achieve such improvement. MRI and clinical responses were uncoupled in adalimumab-treated patients.Conclusion.: We propose that changes of 5.0 for the spine and 2.5 for SI joints define the MIC for the SPARCC MRI indices.