Annals of the rheumatic diseases
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This study was aimed at investigating the frequencies of non-radiographic axial spondyloarthritis (nr-axSpA) and ankylosing spondylitis (AS) diagnoses and their ratios in relation to symptom duration in patients referred because of chronic back pain and suspicion of axial SpA. ⋯ Non-radiographic axial SpA represents an important differential diagnosis of back pain, especially in patients with recent symptom onset.