Non-radiographic axial spondyloarthritis in South America. Burden of disease and differential features with respect to ankylosing spondylitis at time of diagnosis. A comprehensive analysis with a focus on images.

Abstract

Non-radiographic axial spondyloarthritis (nr-axSpA) data from South America are scarce, especially regarding image features. Objective To estimate the frequency of nr-axSpA and ankylosing spondylitis (AS) in a cohort of Argentinian patients with chronic low back pain (LBP) and to analyze the difference between both, with focus on magnetic resonance imaging (MRI) lesions, at diagnosis. Patients with LBP and a diagnosis of axSpA who participated in a reuma-check program were included. All patients with a suspicion of SpA were evaluated using blood analytics, HLA-B27, and images (MRI). Sociodemographic data, SpA features, diagnostic dela,y and clinimetrics were assessed by an operator who was blinded to the patient's test results. On MRI, the presence of SpA lesions was assessed and a concordance exercise was carried out between rheumatologists and radiologist. Of 198 LBP patients, 97 had axSpA, 54% of whom were nr-axSpA. A positive MRI was found in 50%. No difference in terms of disease activity, functional impact, laboratory or treatments between nr-axSpA and AS were found. Higher frequencies of male sex and chronic lesions on sacroiliac MRI were found in AS patients. In the logistic regression, an independent association with AS diagnosis was found: male (odds ratio [OR] 4.8), MRI fat replacement (OR 4.6), MRI sclerosis (OR 7.6), and diagnostic delay of more than 2 years (OR 10). The concordance between rheumatologists and radiologists was considered good to very good (κ 0.7-0.8). The frequency of nr-axSpA was 54%. We found a higher frequency of being male, more SpA features, and a longer diagnostic delay in patients with AS. Patients with AS had more structural lesions, with a good concordance between rheumatologist and radiologist.