Radiographic structural damage in axial spondyloarthritis: is there a preferred way to quantify progression over time? Comparison of blinded versus unblinded mSASSS scoring.

Objectives: Structural progression in spine in axial spondyloarthritis (axSpA) is assessed by conventional radiographs and quantified by the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). Blinded mSASSS scoring might be associated with 'background noise,' and for assessing a slow-progressing disease such as axSpA, high sensitivity to change without loss of specificity is crucial. The aim of this study was to compare the sensitivity to change of blinded vs unblinded application of mSASSS for identification of a preferred way of assessing radiographic damage in axSpA over time.

Methods: Cervical and lumbar radiographcs of axSpA patients participating in a national inception cohort (GErman SPondyloarthritis Inception Cohort) obtained at baseline and after 2 years were scored using the mSASSS by 5 experienced readers, 2 blinded and 3 unblinded to chronology. Mean scores were used for calculations.

Results: Overall, 210 patients (37.3 years, 51% male, 79% human leukocyte antigen B27 positive) were included. The mean baseline mSASSS was 4.2 ± 8.3 vs 3.4±7.9 and mean mSASSS progression was 0.7 ± 2.3 vs 1.0 ± 1.9 for the blinded vs unblinded scoring method, respectively (P = .005). Progression of ≥2 mSASSS units was found in 30 (14.3%) vs 37 (17.6%) patients in blinded and unblinded scoring. In the shift analysis, mSASSS worsening was found in 35 (0.8%) vs 109 (2.2%) and improvement in 4 (0.1%) vs 2 (0.04%) of a total of 4.373 and 4914 vertebral edges in the blinded vs unblinded group, respectively. The majority of progression was found for the development of syndesmophytes in both groups.

Conclusions: More mSASSS progression was detected using unblinded vs blinded scoring. Scoring spinal radiographs with known chronological order seems to be more sensitive to changes.