Diffuse idiopathic skeletal hyperostosis: diagnostic significance of radiographic abnormalities of the pelvis.

Retrospective evaluation of the osseous pelvis in 93 patients with severe diffuse idiopathic skeletal hyperostosis (DISH) revealed 14 locations of radiographic abnormalities. Two osteoradiologists independently studied these sites for abnormalities in a prospective, blinded fashion in 103 patients over the age of 45 years. Lateral radiographs of the thoracolumbar spine were quantitatively and qualitatively evaluated to determine whether DISH, spondylosis deformans, or a normal spine was present. Statistical analysis was performed for evaluation of interobserver reliability, the relationship between pelvic and spinal abnormalities, and the significance and predictive values of pelvic abnormalities for DISH versus non-DISH and DISH versus spondylosis deformans. Although significantly higher frequencies and greater extents of radiographic abnormalities at 10 of 14 pelvic locations were noted for DISH compared with non-DISH, this number decreased to four of 14 locations when compared with spondylosis deformans. The alterations in three of these four pelvic sites consisted of ossification of ligaments. These changes appear to be good indicators of the presence of spinal DISH and support the concept that DISH is an entity separate from spondylosis deformans.