TY - JOUR T1 - Fat Metaplasia in Inflammatory Sacroiliitis and in Nonrheumatic Conditions: A Step Toward Better Characterization JF - The Journal of Rheumatology JO - J Rheumatol SP - 884 LP - 886 DO - 10.3899/jrheum.180050 VL - 45 IS - 7 AU - IRIS ESHED AU - MERAV LIDAR Y1 - 2018/07/01 UR - http://www.jrheum.org/content/45/7/884.abstract N2 - Spondyloarthritis (SpA), a group of inflammatory diseases of which ankylosing spondylitis is the prototype, typically presents with inflammation of the sacroiliac joints (SIJ), or sacroiliitis1,2. The article by Ziegeler, et al in this issue of The Journal3 describes the prevalence of periarticular sacroiliitis-like structural magnetic resonance imaging (MRI) changes of a patient population with low back pain and clinically suspected sacroiliitis. The authors’ main results provide important new insights into the MRI distribution pattern of periarticular fat metaplasia of the SIJ across different age groups in nonrheumatic subjects and numerous specific pathologic conditions.To date, MRI is considered the most sensitive and specific imaging modality for diagnosing and evaluating SIJ inflammation in patients with early disease4. The introduction of biological drugs such as the tumor necrosis factor-α receptor blocker group and their beneficial effect on SpA resulted in an accelerated use of MRI for early detection of sacroiliitis4,5. As a result, an increasing number of SIJ MRI are performed each year on patients with suspected sacroiliitis6. The main acute inflammatory finding detected on MRI, but not on radiographs, is periarticular bone marrow edema, or osteitis. Structural changes such as erosions, sclerosis, and ankylosis can be seen on pelvic radiographs and computed tomography in advanced, already established disease. However, like osteitis, periarticular fatty replacement, or fat metaplasia, is not seen on radiographs and can be reliably detected only on MRI.The Assessment of SpondyloArthritis international Society (ASAS) classification system for axial SpA (axSpA) is based on whether patients meet clinical or imaging criteria5, … Address correspondence to Prof. I. Eshed, Department of Diagnostic Imaging, Sheba Medical Center, Tel Hashomer 52621, Israel. E-mail: iriseshed{at}gmail.com ER -