Imaging in the diagnosis and management of axial spondyloarthritis

Magnetic resonance imaging (MRI) is the imaging modality of choice for diagnosing axial spondyloarthritis (SpA) when the pelvic radiograph is normal or equivocal. Subchodral bone marrow edema (BME) is the primary feature of early SpA, although structural changes, particularly erosions, may also be seen at an early stage. It is unclear whether incorporation of structural lesions enhances the classification performance of a positive MRI definition based on BME alone. Neither spinal imaging nor contrast-enhanced imaging are useful for routine diagnostic evaluation. Fat metaplasia is a key intermediary in the pathway from inflammation to ankylosis, although the histopathology remains to be determined. Both active and structural lesions can be reliably detected and quantified on MRI. Tumor necrosis factor inhibitor therapies ameliorate inflammation; however, it is unclear whether complete suppression of inflammation is necessary to prevent structural damage. Structural lesions on MRI require further validation using computed tomography and prospective follow-up to determine their prognostic significance.