Background Radiographic sacroiliitis is an important outcome in SpA and is mandatory to establish a diagnosis of ankylosing spondylitis (AS). However, few data are available on the factors associated with radiographic sacroiliitis and even less on the predictors of progression from nonradiographic SpA to AS.
Objectives To identify factors associated with radiographic sacroiliitis in a cross-sectional study and predictors of progression to AS in a longitudinal study of SpA patients with positive family history.
Methods The studied cohort consisted of 1,358 patients fulfilling the ASAS criteria for SpA and having at least one first- or second-degree SpA-affected relative, who were recruited by the Groupe Français d'Etude Génétique des Spondylarthrites (GFEGS) and followed longitudinally. Anteroposterior radiographs of the pelvis were examined blindly and independently by 2 qualified examiners (RSN, MB), using the modified New York grading system. Definite radiographic sacroiliitis corresponded to a grade ≥2 bilateral, or grade ≥3 unilateral. Association between definite radiographic sacroiliitis at inclusion and demographic and clinical variables was examined using univariate and multivariate regression analysis. Of the 448 cases without definite sacroiliitis at inclusion, 160 patients were followed-up (with new pelvic X-ray) for 2 to 15 years. Factors associated with progression to definite sacro-iliitis were only assessed by univariate regression analysis because of the smaller study sample.
Results In multivariate analysis, factors positively associated with definite sacroiliitis at inclusion were male sex (p=7x10–8), younger age at disease onset (p=0.04), longer disease duration (p=0.0005), HLA-B27 positivity (p=0.02), inflammatory back pain (p=0.02) and uveitis (p=9.8x10–5). The only negatively associated factor was enthesitis (p=0.002). In longitudinal study, 38 of the 160 patients (23.75%) developed definite sacroiliitis after a mean follow-up duration of 8.8±3.0 years. The only baseline factor associated with progression to definite sacroiliitis throughout follow-up was a low grade radiographic sacroiliitis at inclusion (p=0.002). Uveitis and buttock pain occurring during the follow-up period were also associated with progression to definite sacro-iliitis (p=0.04 and p=0.05, respectively).
Conclusions After an average follow-up duration of almost 9 years, 23.75% of the patients with non-radiographic SpA had developed definitive sacroiliitis (i.e. AS). Factors associated with definitive radiographic sacroiliitis were male sex, younger age at disease, longer disease duration, HLA-B27 positivity, inflammatory back pain, uveitis and lack of enthesitis in the baseline cross-sectional analysis, and low grade radiographic sacroiliitis at inclusion, uveitis and buttock pain during the follow-up in the longitudinal follow-up study.
Disclosure of Interest None declared
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