The role of MRI in the evaluation of spondyloarthritis: a clinician's guide.

Plain radiography remains the benchmark for diagnostic evaluation of spondyloarthritis although MRI has much great sensitivity because it can detect a variety of inflammatory lesions as well as fat metaplasia. So, it is the imaging modality of choice when pelvic radiographs are equivocal and especially when important treatment decisions have to be made. Appropriate imaging includes the use of T1-weighted and short tau inversion recovery sequences of the sacroiliac joint in the tilted coronal plane. If there is localized spinal symptomatology, sagittal scans of the spine may also be helpful. However, routine spinal imaging is not recommended. Current consensus designates a positive MRI for classification purposes as requiring the presence of two definite subchondral inflammatory lesions on a single coronal slice or the presence of one such lesion on two consecutive coronal slices. However, such inflammatory lesions can occur in healthy individuals and in those with nonspecific back pain. Erosions are more specific, and their presence can enhance confidence in the diagnosis. MRI, together with CRP, can be helpful in selecting which patients without radiographic sacroiliitis are most likely to respond to tumor necrosis factor inhibitor therapy. The role of MRI in monitoring of patients with SpA remains unclear although it may be helpful in excluding other sources of back pain. A major unanswered question is whether MRI may be useful in predicting relapse following withdrawal of TNFi in patients who have achieved sustained remission.