PT - JOURNAL ARTICLE AU - Kay Geert A Hermann AU - Katharina Ziegeler AU - Virginie Kreutzinger AU - Denis Poddubnyy AU - Fabian Proft AU - Dominik Deppe AU - Juliane Greese AU - Joachim Sieper AU - Torsten Diekhoff TI - What amount of structural damage defines sacroiliitis: a CT study AID - 10.1136/rmdopen-2021-001939 DP - 2022 Jan 01 TA - RMD Open PG - e001939 VI - 8 IP - 1 4099 - http://rmdopen.bmj.com/content/8/1/e001939.short 4100 - http://rmdopen.bmj.com/content/8/1/e001939.full SO - RMD Open2022 Jan 01; 8 AB - Objectives To propose a data-driven definition for structural changes of sacroiliac (SI) joints in the context of axial spondyloarthritis (axSpA) imaging on a large collective of CT datasets.Methods 546 individuals (102 axSpA, 80 non-axSpA low back pain and 364 controls without back pain) with SI joint CTs were evaluated for erosions, sclerosis and ankylosis using a structured scoring system. Lesion frequencies and spatial distribution were compared between groups. Diagnostic performance (sensitivity (SE), specificity (SP), positive predictive values, negative predictive values and positive and negative likelihood ratios) was calculated for different combinations of imaging findings. Clinical diagnosis served as standard of reference.Results Ankylosis and/or erosions of the middle and dorsal joint portions yielded the best diagnostic performance with SE 67.6% and SP 96.3%. Inclusion of ventral erosions and sclerosis resulted in lower diagnostic performance with SE 71.2%/SP 92.5% and SE 70.6%/SP 90.0%, respectively.Conclusions Sclerosis and ventrally located erosions of SI joints have lower specificity on CT of the SI joint in the context of axSpA imaging. Ankylosis and/or erosions of the middle and dorsal joint portions show a strong diagnostic performance and are appropriate markers of a positive SI joint by CT.Data are available upon reasonable request. Data is available from the corresponding author upon reasonable request.