Imaging of inflammatory rheumatic diseases of the axial skeleton (Sacroiliitis) When and how should we use MRI?

Inflammatory involvement of the sacroiliac joints is the hallmark of the spondyloarthropathies (SpA), in particular ankylosing spondylitis (AS). One leading symptom of SpA is inflammatory back pain (IBP), which may be indicative of sacroiliitis. Conventional diagnostic imaging is insufficient at early stages of sacroiliitis because of the low sensitivity of conventional radiographic scans. In contrast, magnetic resonance imaging (MRI) of the sacroiliac joints depicts both acute and chronic inflammatory changes at all stages of the disease. Disadvantages of MRI are the operator-dependency the lack of standardization, and the relatively high costs. Therefore, in the era of cuts in health care expenditure, the Diagnostic Imaging in Rheumatology Study Group of the Berlin Regional Rheumatology Center, which consists of experienced rheumatologists, skeletal radiologists, and orthopedic surgeons, has compiled a survey of diagnostic imaging in sacroiliitis covering the clinical background, technical details, radiation exposure, and costs. Conventional x-rays remain the standard imaging procedure for the diagnosis of AS. Early sacroiliitis can be detected with higher sensitivity by MRI using contrast agents or fat suppression techniques. Because of its lack of radiation exposure, MRI is the method of choice in children and young women. MRI allows for a more accurate diagnosis of inflammatory back pain by providing objective evidence of inflammation in the sacroiliac joints. Computed tomography can be superior to MRI when bony changes have already occurred.