POS0032 SCORING MRI STRUCTURAL LESIONS IN SACROILIAC JOINTS OF PATIENTS WITH AXIAL SPONDYLOARTHRITIS: HOW MANY SLICES ARE OPTIMAL?
Authors: W. P. Maksymowych, U. Weber, X. Baraliakos, P. Machado, S. Juhl Pedersen, J. Sieper, S. Wichuk, D. Poddubnyy, M. Rudwaleit, D. Van der Heijde, R. B. M. Landewé, J. Paschke, M. Østergaard, R. G. Lambert
Journal: Annals of the Rheumatic Diseases (2021)

Background: There is no international consensus on the optimal number of slices for evaluation of MRI structural lesions in the SIJ. An “all slice” method evaluates lesions from the most anterior slice, defined as the first slice with vertical height of ≥1cm of the SIJ joint cavity, up to the most posterior slice, defined as the most posterior slice where ≥1cm vertical height of the cartilaginous portion is still visible. The SPARCC method scores the transitional slice between cartilaginous and ligamentous compartments as the first slice and then an additional 4 slices anterior to the transitional slice. Objectives: We aimed to investigate inter-reader reliability, the extent of detection of lesions, and frequency of cases with a positive MRI for structural lesions when using an “all slice” approach versus the SPARCC scoring of 5 central slices. Methods: MRI T1W images with DICOM series were available from 148 cases who had MRI performed in the ASAS-Classification Cohort. Seven central readers recorded MRI lesions in an eCRF that recorded global assessments of presence/absence of changes suggestive of axSpA and structural lesions typical of axSpA. Structural lesions per the ASAS definitions were also recorded in consecutive semicoronal slices using the “all slice” approach, but also recording the transitional slice, according to their presence/absence in SIJ quadrants (erosion, fat lesion, sclerosis) or halves (backfill, ankylosis). Structural lesion frequencies were assessed descriptively according to majority agreement (≥4/7) of central readers and also any 2 central readers. Reliability for detection of MRI lesions was compared between central and local readers using the ICC. Results: The mean (SD) (range) number of anterior and posterior slices peripheral to the 5 central slices was 1.0 (1.0) (0-4) and 2.2 (1.8) (0-6) per case, respectively. There were 2 cases (1.4%) where ≥2 readers scored structural lesions in peripheral slices but not in the 5 central slices. The mean percentage of the total structural lesion score that was captured by the 5 central slices was &gt;75% for all types of lesions except ankylosis (59%) (Table 1). Inter-reader reliability was greater for all lesions when assessing the 5 central slices and especially for erosion and backfill (Table 1). Conclusion: The major component of structural lesion data is captured by assessment of 5 slices, which includes the transitional slice and the subsequent 4 anterior slices. Moreover, reliability for detection of structural lesions is substantially worse in peripheral slices. MRI Lesion “All slice” Central 5 slices Peripheral slices P value central vs peripheral slices P value “all slice” vs central slices Mean (SD) Lesion Score Per Case Erosion 2.4 (4.5) (0-22.9) 1.8(3.4) (0-17.1) 0.6 (1.4) (0-10.1) &lt;0.001 &lt; 0.001 Fat lesion 2.5 (5.9) (0-34.0) 1.8 (4.5) (0-25.1) 0.7 (1.8) (0-9.9) &lt; 0.001 &lt;0.001 Sclerosis 2.0 (4.9) (0-39.0) 1.5 (3.6) (0-26.1) 0.5 (1.5) (0-12.9) &lt; 0.001 &lt;0.001 Backfill 0.5 (1.5) (0-12) 0.4 (1.2) (0.0-9.3) 0.1 (0.4) (0-2.7) &lt; 0.001 0.84 Ankylosis 0.5 (3.4) (0-30.7) 0.3 (2.3) (0-20.0) 0.2 (1.2) (0-11.3) 0.10 0.18 Mean (SD) (Range) % of Total Lesion Score in Central vs Peripheral slices Erosion 100% 76.4% (28.9%) (0-100%) 23.6% (28.9%) (0-100%) &lt;0.001 NA Fat lesion 100% 75.4% (26.5%) (0-100%) 24.6% (26.5%) (0-100%) &lt;0.001 NA Sclerosis 100% 79.5% (22.9%) (0-100%) 20.5% (22.9%) (0-100%) &lt;0.001 NA Backfill 100% 86.0% (20.2%) (0-100%) 14.0% (20.2%) (0-100%) &lt;0.001 NA Ankylosis 100% 59.0% (36.4%) (0-100%) 41.0% (36.4%) (0-100%) 0.56 NA ICC of 7 readers (Mean (SD) (Range )) MRI lesion All slices Central 5 slices Peripheral slices Erosion 0.54 (0.15) (0.28-0.84) 0.58 (0.13) (0.34-0.85) 0.40 (0.17) (0.10-0.66) Fat lesion 0.61 (0.18) (0.30-0.89) 0.63 (0.16) (0.35-0.88) 0.52 (0.20) (0.19-0.82) Sclerosis 0.73 (0.18) (0.36-0.94) 0.73 (0.16) (0.36-0.91) 0.67 (0.19) (0.27-0.94) Backfill 0.37 (0.21) (0.10-0.85) 0.39 (0.19) (0.14-0.83) 0.18 (0.23) (0.0-0.80) Ankylosis 0.97 (0.02) (0.91-0.99) 0.99 (0.01) (0.97-1.0) 0.85 (0.10) (0.62-0.98) Disclosure of Interests: None declared.