POS0967 DESCRIPTION OF SACROILIAC CT FINDINGS IN PATIENTS WITH ANKYLOSING SPONDYLITIS AGED OVER 50 YEARS: PRELIMINARY RESULTS OF THE CASIAGE STUDY
Authors: O. Fakih, M. Chouk, C. Prati, D. Wendling, F. Verhoeven
Journal: Annals of the Rheumatic Diseases (2021)

Background: Diagnosis of axial spondyloarthritis (SpA) is nowadays commonly made with the help of pelvic radiography or MRI. However, there is an important inter-observer variability for radiographs, and MRI is subject to possible false positives, and is not the best modality for studying structural lesions. Conversely, pelvic CT has an excellent specificity and appears to be more effective than radiography for the diagnosis of SpA [1]. However, CT findings in patients over 50 years of age have not been studied. Objectives: To describe sacroiliac (SI) joint CT characteristics in patients with ankylosing spondylitis (AS), aged 50 years or older. Methods: An observational, cross sectional study was performed using medical records from Besançon University Hospital’s rheumatology department, which were screened to identify patients with AS. A search was then carried out for patients over 50 years old in the hospital’s imaging archiving system to identify those who had benefited from a CT which included the SI joints in their entirety. Non-inclusion criteria were the existence of pelvic bone lesions and a history of pelvic radiotherapy. For each patient, CT was interpreted using a score previously used by Diekhoff et al. [2], dividing each SI joint into 12 regions, for each of which joint space narrowing (JSN), erosions, and sclerosis are assessed. For this study, we also observed the existence of intra-articular gas and diffuse idiopathic skeletal hyperostosis (DISH) lesions for each region. Quantitative variables are expressed as mean ± standard deviation, qualitative variables as numbers and percentages. Wilcoxon rank-sum test was used to determine factors associated with a higher CT score. Results: A total of 66 patients were included. Mean (SD) age was 65.10 ± 10.59 with a mean (SD) duration of disease of 22.87 ± 14.95 years. 60.29% were male, and 87.04 % were HLA-B27 positive. 40.30% had a bamboo spine. CT findings are described in Table 1. The vast majority of patients have a positive JSN score but significant erosions are found in only a minority of cases. This is partly explained by the fact that 55.9% of the patients had at least one complete bilateral ankylosis (and therefore no erosions) on one of the three slices studied. Bilateral anklylosis was associated with a longer duration of disease (p&lt;0.001) and presence of bamboo spine (p&lt;0.001). Also noteworthy is the low proportion of DISH compared to the general population in this age group, which is 15-25%. Factors associated with a higher total CT score were male sex (p=0.017), longer duration of disease (p&lt;0.001), tobacco use (p=0.033), presence of bamboo spine (p=0.004), absence of DISH (p=0.045) and absence of intra-articular gas (p&lt;0.001). The distribution of lesions appeared to be homogenous over all 24 regions studied (Figure 1). Conclusion: CT findings in AS patients over 50 years of age are mostly represented by changes in joint space, with bilateral ankylosis present in half of the patients. AS appears to be a protective factor for DISH. References: [1]Devauchelle-Pensec V, D’Agostino MA, Marion J, et al. Computed tomography scanning facilitates the diagnosis of sacroiliitis in patients with suspected spondylarthritis: Results of a prospective multicenter French cohort study. Arthritis Rheum 2012; 64 :1412–9. doi:10.1002/art.33466 [2]Diekhoff T, Hermann K-GA, Greese J, et al. Comparison of MRI with radiography for detecting structural lesions of the sacroiliac joint using CT as standard of reference: results from the SIMACT study. Ann Rheum Dis 2017; 76 :1502–8. doi:10.1136/annrheumdis-2016-210640 Table 1. Sacro-iliac CT findings using a score modified from Diekhoff et al. Mean total score (range 0-108) 70.36±38.90 Presence of joint space narrowing 58 (85.29 %) Presence of erosion 20 (29.41 %) Presence of sclerosis 15 (22.06 %) Presence of Intra-articular gas 22 (32.35 %) Presence of DISH 3 (4.41 %) Figure 1. Mean scores per region in the anterior, central and posterior SI slices (JSN: joint space narrowing (0-4), Ero: erosions (0-3), Scl: sclerosis (0-2)). Disclosure of Interests: None declared.