What amount of structural damage defines sacroiliitis: a CT study

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.

Automated summary

This study proposes a data-driven definition for structural changes in the sacroiliac (SI) joints in the context of axial spondyloarthritis (axSpA) imaging. Evaluation of 546 individuals with SI joint CTs showed that ankylosis and/or erosions of the middle and dorsal joint portions had the best diagnostic performance. Sclerosis and ventrally located erosions had lower specificity on SI joint CT imaging.