Insights into axial spondyloarthritis features and the development of imaging evidence of sacroiliitis during long-term follow-up in routine clinical practice

To analyse characteristics and SpA features of newly diagnosed patients with radiographic (r-) versus non-radiographic (nr-)axSpA, and nr-axSpA patients fulfilling the imaging versus clinical arm of the ASAS classification criteria. Furthermore, this study explored whether patients from the clinical arm developed imaging evidence of sacroiliitis during follow-up. Consecutive newly diagnosed axSpA patients included in the prospective GLAS cohort between 2009 and 2019 were analysed. Demographic data and SpA features were compared between groups using multivariable logistic regression analysis. Patients fulfilling the clinical arm were evaluated for the development of radiographic sacroiliitis during follow-up. 305 patients with a recent axSpA diagnosis were included. Mean age was 38 ± 12 years, 55% were males, median diagnostic delay was 6 (IQR 2–13) years, and 75% were HLA-B27+. Patients diagnosed with r-axSpA (n = 170; 56%) were more often male and had more often elevated CRP than patients diagnosed with nr-axSpA. Patients with nr-axSpA had more often inflammatory back pain and a positive family history of SpA. Clinical diagnosis was made without imaging evidence of sacroiliitis in 38 (12%) patients. Only 2 (5%) of these patients later developed sacroiliitis on imaging (median follow-up 8 years). Overall, diagnosed and classified axSpA patients have similar clinical presentation and disease burden. In approximately 1 in 10 patients, axSpA diagnosis was made without imaging evidence of sacroiliitis, with a negligible number developing sacroiliitis on imaging during long-term follow-up. Imaging may improve diagnostic confidence, which can prevent reconsideration of the diagnosis and reduce inappropriate management decisions and expectations.