Background Fat lesions (FL) have been shown to follow resolution of inflammation in the spine of patients with axial spondyloarthritis (SpA) (1), and to predict development of new syndesmophytes (2). Thus, scoring of FLs in the spine may constitute both an important measure of treatment efficacy and a surrogate marker for new bone formation.
Objectives To develop and validate a new scoring method for FLs in the spine, the CanDen Fat SpA Spine Score (FASSS), which addresses the localization and phenotypic diversity of FLs in SpA.
Methods The fat scoring method comprises different types of FLs, which are defined according to their anatomical location and are recorded dichotomously (present/absent) at each vertebral endplate (from C2 lower to S1 upper) according to the definitions of the Canada-Denmark MRI working (3). The scoring range per disco-vertebral unit (DVU) for the cervical (C) spine is 0-8, and for the thoracic (T) and lumbar (L) spine is 0-24, resulting in a total scoring range of 0-456 for all 23 DVUsTwo rheumatologists evaluated MRI scans obtained at two time points (mean 1.5 years (SD 0.5)) in chronological order of 67 patients (exercise 1). After exercise 1 the scoring methodology and reference image set were revised based on discrepant cases. In a nested case study design, the two readers re-read 30 randomly selected pairs of MRI scans from the first exercise together with 40 new pairs of MRI scans (exercise 2) (mean 1.7 years (SD: 0.8)).
Results In exercise 2, the change in fat scores ranged from -33 to 48 for reader A and from -38 to 54 for reader B. Inter-observer ICC scores were high to very high for the FASSS baseline scores, and improved substantially in change scores from exercise 1 to 2 (Table). Inter-observer intra-class correlation coefficients (ICCs) for baseline scores were high for all spinal segments, and change scores improved from small to moderate for the C spine, from moderate to high for the L spine and remained very high for the T spine. This was particularly notable for the 30 patients evaluated in both exercises.
Conclusions The FASSS therefore meets essential validation criteria for further assessment in axial SpA, and for follow-up of SpA in clinical trials and practice.
Chiowchanwisawakit et al. ARD 2010;
Chiowchanwisawakit et al. AR 2011;
Østergaard et al. J Rheum 2009
Disclosure of Interest None Declared