Selection of X-ray versus magnetic resonance imaging as a first-line imaging modality for diagnosing axial spondyloarthritis

INTRODUCTION: To determine the cut-off values for age and symptom duration that could be used in selecting preferential first-line imaging modality of sacroiliac joints [X-ray versus magnetic resonance imaging (MRI)] for diagnosing axial spondyloarthritis (axSpA). METHODS: This retrospective cohort study included 388 patients newly diagnosed with axSpA. Patients were classified into radiographic axSpA (n = 322) and non-radiographic axSpA (n = 66) groups according to the fulfilment of modified New York criteria by X-ray. Patient characteristics of the two groups were compared. Receiver operating characteristic (ROC) curve analysis was conducted to determine the cut-off values for age and symptom duration that best distinguish non-radiographic axSpA from radiographic axSpA. RESULTS: Compared with patients with radiographic axSpA, those with non-radiographic axSpA were younger at diagnosis (35.7 ± 11.3 years versus 26.8 ± 7.8 years, p < 0.001) and had shorter symptom duration [5.1 (2.1–12.0) years versus 1.0 (0.5–3.2) years, p < 0.001]. ROC analysis showed that age > 33.5 years at diagnosis [area under the curve (AUC): 0.734] and symptom duration > 4.1 years (AUC: 0.787) were the cut-off values that best discriminate radiographic axSpA from non-radiographic axSpA. CONCLUSION: The best cut-off values for age and symptom duration for predicting radiographic sacroiliitis are 33.5 and 4.1 years, respectively. It is reasonable to use X-ray as a first-line imaging modality in patients older than 33.5 years with a symptom duration longer than 4.1 years, and use MRI as a first-line imaging in patients younger than 33.5 years with a symptom duration less than 4.1 years.