Background/Purpose: Psoriatic arthritis (PsA) is an inflammatory arthritis associated with various rheumatological manifestations, such as arthritis or enthesitis, predominantly in the peripheral skeleton. However, the axial skeleton may be affected, as shown clinically or by conventional radiographs in up to 70% of patients with peripheral involvement. While there are studies comparing joint damage on standard radiography between patients with PsA and patients with ankylosing spondylitis [1], to our knowledge, no study has specifically evaluated the extent of structural lesions of the sacroiliac joints (SIJs) on computed tomography (CT) in patients with PsA compared with healthy controls. Our objective was to describe SIJ CT characteristics in patients with PsA and compare them with those of age- and sex-matched controls.

Methods: An observational retrospective study was performed using medical records from Besançon and Dijon University Hospital’s rheumatology departments, which were screened to identify patients with PsA, according to the CASPAR criteria. A search was then carried out for patients in the hospitals’ imaging archiving system to identify those who had undergone a CT which included the SIJs in their entirety. Non-inclusion criteria were the existence of pelvic bone lesions and a history of pelvic radiotherapy. Each patient was then matched with a control of the same age and sex, recruited through the hospital’s imaging archiving system.

For each individual, CT was interpreted by two independent readers using a score previously used by Diekhoff et al. [2], dividing each SIJ 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 were compared using Student’s t-test. Qualitative variables were compared using the Chi-2 test.

Results: 48 patients and 48 controls were included. Mean (SD) age was 54.76 ± 12.91 in the PsA group and 54.74+12.87 in the control group. 26 (54.18%) were male in both groups. In PsA patients, mean (SD) disease duration was 22.87 ± 14.95 years, 10 (43.48 %) were HLA-B27 positive, and 1 (2.86%) had a bamboo spine. CT findings are described in table 1. The only lesion found significantly more frequently in PsA patients was erosion, which appeared to be preferentially located on the anterior and middle regions of the SIJs (Figure 1). A positive CT scan (significant joint space narrowing, erosion and/or sclerosis) was found in 15 (32.61%) of the patients with peripheral involvement and 6 (30.00%) of the patients with axial involvement.

Conclusion: The CT characteristics of SIJs from patients with PsA were similar to those of age- and sex-matched controls, but with a higher prevalence of erosions, found in 18% of PsA patients.

1. Jadon DR et al. Axial Disease in Psoriatic Arthritis study: defining the clinical and radiographic phenotype of psoriatic spondyloarthritis. Ann Rheum Dis. 2017;76.
2. Diekhoff T 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(9).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparison-of-sacroiliac-ct-findings-in-patients-with-and-without-psoriatic-arthritis-results-of-the-casipsa-study/