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. 2022 Jan;8(1):e001939.
doi: 10.1136/rmdopen-2021-001939.

What amount of structural damage defines sacroiliitis: a CT study

Kay Geert A Hermann #  1 , Katharina Ziegeler #  2 , Virginie Kreutzinger  3 , Denis Poddubnyy  4 , Fabian Proft  4 , Dominik Deppe  2 , Juliane Greese  2 , Joachim Sieper  4 , Torsten Diekhoff  2
Affiliations

What amount of structural damage defines sacroiliitis: a CT study

Kay Geert A Hermann et al. RMD Open. 2022 Jan.

Abstract

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.

Keywords: ankylosing spondylitis; ankylosis; erosion; low back pain; sclerosis.

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Conflict of interest statement

Competing interests: KGAH reports lecture fees from AbbVie, MSD and Novartis outside the submitted work. KZ reports funding (research grant) from the Assessment of Spondyloarthritis international Society (ASAS) during the conduct of this study. DP reports grants and personal fees from AbbVie, Eli Lilly, MSD, Novartis, Pfizer and personal fees from Bristol-Myers Squibb, Roche, UCB, Biocad, GlaxoSmithKline, Gilead, Janssen, Samsung Bioepis and UCB outside the submitted work. FP reports grants and personal fees from Novartis, Lilly and UCB, as well as personal fees from AbbVie, AMGEN, BMS, Hexal, MSD, Pfizer and Roche outside the submitted work. JS reports personal fees from AbbVie, Janssen, Merck, Novartis, UCB and Lilly, outside the submitted work. TD reports funding (research grant) from the ASAS and lecture fees from Canon Medical, AbbVie, MSD and Novartis pharma, outside the submitted work. For all other authors, none were reported.

Figures

Figure 1
Figure 1
Patient flow and clinical characteristics. Significantly higher values/proportions compared with non-axSpA LBP group are marked with an asterisk (*). P values derived from Fisher’s exact test or unpaired t-tests. axPsoA, axial psoriatic arthritis; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; CRP, C reactive protein; LBP, low back pain; Nr-axSpA, non-radiographic axial spondyloarthritis; ns-LBP=non-specific low back pain; OA, osteoarthritis; OC, osteitis condensans; r-axSpA, radiographic axial spondyloarthritis (formerly ankylosing spondylitis); HTO, Hyperostosis triangularis.
Figure 2
Figure 2
Scoring system. Segmentation of joint in ventral, middle, and dorsal parts, based on oblique coronal imaging, parallel to the second sacral vertebra. Ventral part (regions 1–8): no neural foramina visible. Middle part (regions 9–16): sacral foramina are depicted. Dorsal part (regions 17–24): sacral nerve roots and spinal canal are depicted. Erosion means hypodense disruption of the cortex of at least 1 mm, excluding tubular structures such as bone canals. Sclerosis means well demarcated increase of density of periarticular bone. Ankylosis means growth of bone across the joint space; partial ankylosis means some areas of visible joint space remain; complete ankylosis means no joint space is discernible. Graphic adapted from Diekhoff et al.
Figure 3
Figure 3
Relative frequency of lesions across regions (%). Different colours for patient groups: blue for non-axSpA LBP controls, green for ax-SpA and red for non-axSpA LBP; shade of colour denoting frequency from white (lowest) to dark (highest) for ease of visual interpretation. Significantly higher frequencies (compared with non-axSpA LBP) are marked with asterisks (*).
See this image and copyright information in PMC

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