Our data showed that almost 10% of the patients with SpA had late-onset of symptoms. Moreover, they had higher disease activity, worse physical function and lower spine radiographic damage than A-O SpA patients. Additionally, the ASAS classification criteria had the best performance and might be used in clinical practice.

The lack of specific biomarkers to evaluate disease activity in patients with ankylosing spondylitis (AS) is a relevant clinical challenge. The aim was to assess the role of total spine magnetic resonance imaging (MRI) in AS patients with clinical doubt between activity or chronicity. METHODSA total of 57 AS patients, according to the New York criteria, were included in this 2-year prospective study. The inclusion criterion was the clinical doubt between to be or not to be with disease activity, considering standard tools, including inflammatory back pain, peripheral involvement, extra-articular manifestations and C-reactive protein (CRP). The patients were divided in two groups (A: pain + low CRP; B: no symptoms + high CRP). All patients performed total spine MRI and the reading was performed by blinded radiologist, considering SPARCC methodology. After that, an expert rheumatologist used it to make major clinical decision. A positive spine MRI was defined when three or more bone marrow edema signals were found, according to the OMERACT. RESULTSPositive MRI was observed in 40 and 30% of group A and B, respectively. Using the global evaluation (clinical, lab and imaging information) performed by expert rheumatologist as gold-standard, the concordance between positive MRI and overall disease activity was observed in almost 70% of AS patients (r = 0.36, p = 0.01), especially in group A. On the other hand, higher inflammation severity and area score was more found in group B (15.7 ± 7.5 and 9.9 ± 6.7; p = 0.048, respectively). After 12 and 24 month follow-up, most of the patients remained with the same medical decision, suggesting good assertiveness over time. CONCLUSIONOur data showed whole spine MRI could be used as an important tool for a suitable clinical decision between disease activity and other non-inflammatory causes of pain in patients with AS.