OP0253 STRUCTURAL DAMAGE IN AXIAL SPONDYLOARTHRITIS: IS THERE A PREFERRED WAY TO ASSESS PROGRESSION OVER TIME?

Background: Axial spondyloarthritis (axSpA) is characterized by development of structural damage in the spine, assessed by conventional radiographs (CR). The modified Stokes Ankylosing Spondylitis Scoring System (mSASSS) includes all the SpA-relevant CR findings and is the most frequently used scoring system for quantification of spinal structural damage in patients (pts) with axSpA. Radiographic progression over 2 years using mean mSASSS progression, scored by a blinded ‘paired’ (sets of CRs of the same patient) approach, is considered as a key treatment outcome reflecting structural progression in clinical trials. However, this approach has been accompanied by questions about the influence of pts showing mSASSS ‘improvement’, indicating possible disappearance of syndesmophytes over time, something ‘naturally unexpected’. Objectives: To investigate the performance of mSASSS in assessing spinal radiographic damage and progression in axSpA pts using different approaches of CR evaluations. Methods: Complete sets (cervical and lumbar CRs) from the German SpA Inception Cohort (GESPIC) at baseline and after 2 years were blinded to all clinical and demographic characteristics and then scored using the mSASSS by 5 different experienced readers, 2 blinded and 3 unblinded to the timepoint of CR performance. The final mSASSS score was calculated as a mean of 2 (blinded) or 3 (unblinded) readers. Descriptive statistics, cumulative probability plots and shift analyses (agreement of 2/2 readers in the blinded and 2/3 readers in the unblinded group) were performed for each reader group. Results: A total of 210 pts (mean age 37.3y, 51% male, 79% HLA-B27+) with non-radiographic (n=115) and radiographic (n=95) axSpA at baseline were included. The mean mSASSS at baseline was 4.3±8.3 vs. 3.4±7.9, while the mean progression was 0.7±2.3 vs.1.0±1.9 mSASSS units for the blinded vs. the unblinded group, respectively (Figure). On the patient level, progression of ≥2 mSASSS units was found in 30 (14.3%) vs. 37 (17.6%) pts in the blinded vs. the unblinded group, while agreement between groups was seen in 179 (85.2%) pts, 18 (8.9%) pts for progression and 161 (76.7%) for no progression. In the analysis of ‘definite’ CR findings (only scores of 2=syndesmophytes or 3=ankylosis), the mean mSASSS score at baseline was 3.3±8.0 vs. 2.6±7.2 and the mean radiographic progression was 0.6±2.4 vs. 0.8±2.1 mSASSS units for the blinded vs. the unblinded group, respectively (Figure). On the patient level, progression was found in 37 (17.6%) vs. 33 (15.7%) pts in the blinded vs. the unblinded group, while agreement between groups was seen in 188 (89.5%) pts, 24 (11.3%) for progression and in 164 (78.1%) pts for no progression. In the shift analysis, mSASSS worsening was found in 35 (0.8%) and mSASSS ‘improvement’ in only 4 (0.1%) out of a total of 4.373 vertebral edges (VE) analyzed in the blinded and in 109 (2.2%) and 2 (0.04%), respectively, out of a total of 4.914 VE analyzed in the unblinded group (Table). The majority of progression was found for the development of ‘definite’ signs of progression in both the blinded (25/35, 71.4%) and the unblinded (61/109, 56%) group, while more VE showing ‘minor’ (only scores of 1=sclerosis, squaring, erosion) signs of progression were found in the unblinded (48/109, 44%) vs. to the blinded (10/25, 28.6%) group. Conclusion: Despite lower mean baseline mSASSS, higher mean mSASSS progression was found using the unblinded approach, while in the shift analysis the unblinded approach was also more specific, confirming the absence of ‘improvement’ of radiographic damage over time. These results were similar in the analysis on the patient’s level. The scoring approach and the influence of ‘minor’ radiographic changes should be taken into account for avoiding the so-called ‘background noise’ in the evaluation of mSASSS. Acknowledgements: GESPIC was initially supported by the BMBF. As a consequence of the funding reduction by BMBF according to schedule in 2005 and stopped in 2007, complementary financial support has been obtained also from Abbott, Amgen, Centocor, Schering–Plough, and Wyeth. Starting from 2010, the core GESPIC cohort was supported by AbbVie. Disclosure of Interests: None declared