Magnetic resonance imaging (MRI) of the sacroiliac (SI) joints has rapidly gained attention as a potentially useful imaging modality in the diagnostic process of patients with chronic back pain. From a rheumatological point of view, MRI of the SI joints seems particularly useful in evaluating patients with inflammatory back pain (IBP), because it may help make or exclude a diagnosis belonging to the spectrum of spondyloarthritis (SpA). The prototype diagnosis in the spectrum of SpA obviously is ankylosing spondylitis (AS) or Bechterew’s disease. It is useful to keep in mind that AS is a classifying diagnosis, based on clinical and radiological features articulated in the 1984 modified New York criteria1. The radiological criterion requires radiological sacroiliitis on a plain radiograph of the pelvis, and erosions belong to the features compatible with that. Two nuances should be mentioned here: The developers of the modified New York criteria investigated a group of classic AS patients, implying that many of these patients showed features that make AS classic, namely syndesmophytes or bamboo spine. This is why the modified New York criteria (and other sets of classification criteria in general) fail to detect patients with early disease and possibly even patients with mild or moderate disease. A second nuance is that the radiological criterion suffers from important interobserver variation, especially in …
Address correspondence to Dr. R. Landewé, Maastricht University Medical Center, Department of Internal Medicine/Rheumatology, P.O. Box 5800, 6202AZ Maastricht, The Netherlands. E-mail r.landewe{at}mumc.nl