Assessing structural changes in axial spondyloarthritis using a low-dose biplanar imaging system.

OBJECTIVES Patients with axial SpA experience repeated spine imaging. EOS is a new low-dose imaging system with significantly lower irradiation than conventional radiography (CR). The objective was to explore the EOS performances compared with CR for the classification and follow-up of SpA. METHODS We performed an observational, cross-sectional, single-centre study including SpA patients (definite diagnosis by expert opinion) and control patients [definite chronic mechanical low back pain (cLBP)]. All patients underwent pelvic and frontal and lateral CR of the entire spine and two-dimensional (2D) EOS imaging on the same day. Images were blindly assessed for sacroiliitis [modified New York criteria (mNY)] and for ankylosis of the spine [modified Stoke AS Spine Score (mSASSS)]. Global ease of interpretation was rated on a scale of 0-10. The primary outcome was intermodality agreement, with an a priori defined non-inferiority limit of 0.7. Interobserver, intra-observer and intermodality agreement were measured by kappa, weighted kappa, intraclass correlation coefficient and Bland-Altman plots. RESULTS Forty-eight SpA patients [mean age 47.6 years (s.d. 14.9), symptom duration 21.4 years (s.d. 13.3), 35 (70%) men] and 48 cLBP controls [mean age 49.1 years (s.d. 10.7), 9 (22.5%) men] were included. Intermodality agreement between EOS and CR was 0.50 (95% CI 0.26, 0.75) and 0.97 (95% CI 0.95, 0.98) for sacroiliitis and mSASSS, respectively. Ease of interpretation was greater for CR [8.2 (s.d. 0.9)] compared with EOS [7.2 (s.d. 0.8), P < 0.0001). CONCLUSION Our results suggest that EOS could replace CR for the follow-up of structural damage of the spine, but its place in the classification of sacroiliitis needs to be further explored.