MAGNETIC-RESONANCE-IMAGING AND AXIAL INVOLVEMENT IN SPONDYLARTHROPATHIES - DELINEATION OF THE SPINAL ENTHESES

We used magnetic resonance imaging in a prospective cross-sectional st udy to evaluate the components of axial involvement in spondylarthropa thies, to determine whether the entire intervertebral disk is an enthe sis and to gauge how useful this imaging technique is in detecting ent hesitis of the spine. Thirty-one patients with spondylarthropathies an d 14 controls with mechanical spinal disease were included. Images of the thoracic and lumbar spine were obtained using plain radiography, r adionuclide bone scanning, and magnetic resonance imaging (sagittal se ctions, T1-weighted sequences before and after gadolinium injection an d fat saturation and T2-weighted sequences). Magnetic resonance imagin g signal abnormalities reflected inflammation and hypervascularization of the subchondral bone underlying the affected entheses (low signal enhancing after gadolinium and fat saturation on T1 images, high signa l on T2 images). These abnormalities were often visible early in the d isease process, at a time when there were not yet any clinical manifes tations or radiographic or bone scan changes. In addition to showing i nvolvement of the classic spinal entheses, magnetic resonance imaging also demonstrated evidence of inflammation and hypervascularization of the central part of the vertebral endplates and intervertebral disks, confirming that the center of the disk is an enthesis and that inflam matory enthesitis is the mechanism underlying at least some cases of d iscitis seen in patients with spondylarthropathies.