Validation of the Spondyloarthritis Research Consortium of Canada magnetic resonance imaging spinal inflammation index: Is it necessary to score the entire spine?

Objective. The Spondyloarthritis Research Consortium of Canada (SPARCC) magnetic resonance imaging (MRI) spinal inflammation index has been developed to objectively measure inflammation in ankylosing spondylitis (AS) and to assess change in response to therapeutic intervention. Scoring of the entire spine limits feasibility and a scoring method that records inflammation in only the more severely affected spinal segments may improve feasibility without sacrificing performance. Methods. MRI films of 68 patients with AS were assessed in random order by 2 blinded readers. Interreader reliability was assessed by intraclass correlation coefficient. Pre- and posttreatment MRI films of 29 patients randomized to placebo or anti-tumor necrosis factor a (anti-TNF alpha) therapy were read by readers blinded to chronology, and responsiveness was assessed by effect size and standardized response mean. The performance of scores based on 6, 8, 10, and all 23 spinal discovertebral units (DVU) was compared. Results. The median number of affected spinal levels per patient was 6.0 and 62% of all affected levels were included when analysis was limited to only the 6 most severely affected levels per patient. Comparison of DVU scores that were limited to only the more severely affected DVU (6-, 8-, 10-DVU score) with scores for all 23 spinal DVU showed excellent interreader reliability for status and change scores (Spearman's correlation >0.90) as well as similar construct validity. Responsiveness to anti-TNF alpha therapy was greater when the more limited scoring methods were used and was greatest with the 6-DVU score. Conclusion. The SPARCC MRI spinal inflammation index performs better when analysis is limited to a maximum of 6 most severely affected levels compared with assessment of the entire spine. This should improve its feasibility in clinical trials and research.