Natural course of bone marrow oedema on magnetic resonance imaging of the sacroiliac joints in patients with early inflammatory back pain: a 2-year follow-up study

Objectives: To describe the distribution and evolution over time of bone marrow oedema (BME) on magnetic resonance imaging of the sacroiliac joint (MRI-SIJ) in patients with recent-onset inflammatory back pain (IBP) suspected for axial spondyloarthritis (axSpA). Method: A 2-year follow-up study with annual MRI-SIJ was conducted in patients with IBP of duration <= 2 years. Each SIJ was divided into quadrants and MRI scores were analysed on a per-patient and per-SIJ quadrant basis. The presence of BME in each SIJ quadrant was recorded. Fulfilment of the Assessment of SpondyloArthritis international Society (ASAS) criteria for axSpA was assessed at baseline and at follow-up. Results: At baseline, 68 patients (38% male; mean age 34.9 +/- 10.3 years) were included. BME was visible at baseline in 24 (35%) patients, all fulfilling the ASAS axSpA criteria. Twenty-three of these 24 patients had a follow-up MRI. Not taking into account the baseline MRI, three (13%) of these 23 patients would no longer fulfil the ASAS criteria during follow-up because of subsiding BME. Forty-four (65%) patients had a negative baseline MRI, of whom 39 had a follow-up MRI available. New BME at follow-up meant that three (8%) of these 39 patients now fulfilled the ASAS criteria. At follow-up, baseline BME lesions subsided completely in 47% of SIJ quadrants (range 33-71%) whereas new BME lesions were detected in 8% of SIJ quadrants (range 2-11%). Conclusions: BME shows a fluctuating course in patients with early IBP suspected for axSpA. This may have an impact on diagnosis and the overall performance of the ASAS axSpA criteria.