Objectives: Radiographic sacroiliitis is an important outcome in SpA and is considered a hallmark to ascertain the diagnosis of AS. The aim of the current study was to investigate factors associated with the presence of radiographic sacroiliitis at baseline and the predictors of progression to AS in a family cohort of SpA.
Methods: A total of 953 patients fulfilling the Assessment of SpondyloArthritis international Society criteria for SpA and having at least one first- or second-degree SpA-affected relative were included. Pelvic X-rays were examined blindly and independently by two qualified examiners using the modified New York criteria. Of the 446 cases without definite sacroiliitis at inclusion, 145 patients were followed up with new pelvic X-rays for 3-15 years. Regression analysis was used to assess factors associated with definite radiographic sacroiliitis.
Results: Factors independently associated with radiographic sacroiliitis at inclusion were male sex, younger age at disease onset, longer disease duration, inflammatory back pain, uveitis and lack of enthesitis. During the follow-up, 27.3% of the patients with axial SpA developed definite sacroiliitis, whereas there was no progression in patients with peripheral SpA. After 15 years of follow-up, a Kaplan-Meier estimate of the proportion of patients with definite radiographic sacroiliitis reached 68.5%. Factors associated with progression to definite sacroiliitis were a low-grade radiographic sacroiliitis at inclusion, occurrence of buttock pain and the absence of peripheral arthritis during the follow-up period.
Conclusions: These data confirm that progression to radiographic disease occurs most often over time in axial SpA patients.
Keywords: ankylosing spondylitis; non-radiographic axial spondyloarthritis; radiographic sacroiliitis; spondyloarthritis; undifferentiated spondyloarthritis.
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