Demographic and clinical differences between ankylosing spondylitis and non-radiographic axial spondyloarthritis: results from a multicentre retrospective study in the Lazio region of Italy.

Objective Axial spondyloarthritides (axSpA) are a group of disorders that share similar pathogenetic mechanisms and clinical picture. The aim of this retrospective multicentric study was to evaluate demographic and clinical differences between ankylosing spondylitis (AS) and non-radiographic axSpA (nr-axSpA) patients. Methods Patients from 7 rheumatological centres in the Lazio region of Italy were included from January 1st, 2010 to April 1st, 2018, if they had undergone pelvic and/or spine radiographs or magnetic resonance imaging (MRI). Images were evaluated by one experienced radiologist in each centre who already had the clinical suspicion of axSpA. Clinical and therapeutic data were collected at the last observation visit. Categorical variables were presented with percentages and analysed by Chi squared test. Continuous variables were expressed as mean +/- standard deviation and compared using the parametric unpaired t-test or the non-parametric Mann-Whitney U-test, when appropriate. p-values <0.05 were considered significant. Results 210 axSpA patients were included: 65.2% with AS and 34.7% with nr-axSpA. When comparing the two groups, AS patients had longer disease duration, were older, were more frequently males, had a greater diagnostic delay and a higher body mass index than the nr-axSpA patients (p<0.0001, p<0.0001, p=0.003 p=0.007, and p=0.04, respectively). The peripheral joints of the nr-axSpA patients were more frequently involved, had higher frequency of inflammatory bowel disease, higher C-reactive protein levels and lower frequency of HLA-B27 positivity (p=0.005, p=0.007, p=0.01, and p=0.01, respectively). TNF inhibitors were used in 87.8% patients with AS and 78.3% with nr-axSpA (p=0.04). More fat metaplasia was observed on MRI in the nr-axSpA group than in the AS group at sacroiliac joints (p=0.003), and more backfills were detected in the AS group on spine-MRI (p=0.003). Spine-bone marrow oedema was more prevalent in AS than in nr-axSpA (p=0.04), and more sclerosis and backfill were found in AS (p=0.003 and p=0.01, respectively). Conclusion In clinical practice, distinctive features in AS and nr-axSpA patients emerged. Imaging is crucial in guiding the choice of treatment in order to control disease activity and inflammation.