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

Abstract

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. 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. 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. We propose that changes of 5.0 for the spine and 2.5 for SI joints define the MIC for the SPARCC MRI indices.