Background/Purpose: Sacroiliitis, as detected by plain radiographs of the sacroiliac joints (SIJ), has been reported in a third of the psoriatic arthritis (PsA) population. (1) Referred to as radiographic axial spondyloarthritis (r-axSpA), this finding represents a late axial disease. For detection of an non –radiographic ( nr-axSpA) axial disease in the presence of normal pelvic XR (non-radiographic axSpA – nr-axSpA), MRI is commonly applied. Yet, there is limited data on the frequency of nr-axSpA in the PsA population. The purpose of our study was to establish the prevalence of nr-axSpA in a consecutively recruited observational cohort of PsA.

Methods: Adult PsA patients from the Tel Aviv Medical Center Rheumatology Clinic were consecutively recruited into the study. All patients underwent clinical evaluation, CRP and HLA-B27 tests, plain XR of the SIJs and MRI of the entire spine and SIJs. Spinal sagittal T1-W and STIR images of the spine and semi-coronal T1-W and T2-W with fat saturation of the SIJs were performed. Radiographs were independently read by two musculoskeletal radiologists (NY criteria)(2), and MRI examinations were interpreted by a third musculoskeletal radiologist using ASAS criteria and global (both structural and acute) SIJ scoring(3), all blinded to the clinical data. Data were analyzed by SPPS Version 20.0. Categorical descriptive data were presented as absolute values with percentages and continuous data as mean (standard deviation). Group comparisons of categorical data were performed by χ²-tests and of continuous data by the Mann-Whitney U-test.

Results: Sixty-nine patients were recruited into the study. For 51 patients, all imaging set was available at the time of the interim analysis. Demographic and clinical data is presented in Table 1. All patients but two were HLA-B27 negative. Inter-reader agreement between the two XR readers was good (κ=0.73). Nr-axSpA was detected in 20% of the cohort, and r-axSpA was detected in 23%. 12% of patients demonstrated false positive sacroiliitis by XR not confirmed by MRI. MRI positive sacroiliitis (ASAS/Global) was detected in 29%/43%, respectively. Extensive psoriasis assessed by PASI was associated with global MRI sacroiliitis presence (p 0.03). Clinical indices of peripheral and spinal disease activity did not correlate with MRI sacroiliitis. There was no difference in the sacroiliitis prevalence among male and female sub-groups. Biologic naïve patients demonstrated similar rates of sacroiliitis as patients exposed to biologic therapies.

Conclusion: This is the first study to report the frequency of nr-axSpA (20%) in an observational PsA cohort. Our study also emphasizes the limitations of pelvic XR in diagnosing clinical sacroiliitis. Table 1. Cohort demographics and clinical data.

References: 1.Gladman D. Axial disease in psoriatic arthritis. Curr Rheumatol Rep 2007. 9 (6):455 -60. 2. van der Linden S, Valkenburg HA, Cats A. Evaluation of diagnostic criteria for ankylosing spondylitis. A proposal for modification of the New York criteria. Arthritis Rheum1984;27:361–8. 3. Song IH et al. Relationship between active inflammatory lesions in the spine and sacroiliac joints and new development of chronic lesions on whole-body MRI in early axial spondyloarthritis: results of the ESTHER trial at week 48. Ann Rheum Dis. 2011 Jul;70(7):1257-63

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/prevalence-of-non-radiographic-axial-spondyloarthritis-in-psoriatic-arthritis-a-single-center-observational-study/