The seronegative arthropathies comprise a group of related inflammatory arthritides, which are classified together because they primarily affect the entheses and share many clinical and imaging features. The principal clinical entities of this group include ankylosing spondylitis (AS), psoriatic arthritis (PA), reactive arthritis, enteropathic spondylitis (ES) and undifferentiated spondyloarthropathy. Enthesitis is the key pathological lesion in the seronegative arthropathy.
The choice of imaging modality depends on whether the suspected enthesitis/inflammation is in the axial or peripheral skeleton. If it is in the former, MRI is the modality of choice. If in the latter, and the suspected site of enthesitis is clinically accessible to an ultrasound probe, then ultrasound would be the preferred method. Plain radiograph plays limited role in diagnosing early inflammation.

Educational aims:
• To demonstrate the skeletal manifestations of seronegative spondyloarthropathies and to illustrate typical appearances on conventional radiography, ultrasound and magnetic resonance (MR) imaging
• To highlight the role of MR imaging and ultrasound in identification of early joint and bone involvement and to illustrate the changing radiological features with disease progression

References:
• MRI in Seronegative Spondyloarthritis: Imaging Features and Differential Diagnosis in the Spine and Sacroiliac Joints. Clarissa Canella1 , Bruno Schau, Elisio Ribeiro, Bruna Sbaffi and Edson Marchiori. American Journal of Roentgenology. 2013;200: 149-157
• Jacobson JA, Girish G, Jiang Y et-al. Radiographic evaluation of arthritis: inflammatory conditions. Radiology. 2008;248 (2): 378-89.
• Tan AL, McGonagle D. Imaging of seronegative spondyloarthritis. Best Practice Res Clinical Rheumatology 2008;22(6):1045-59.

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