Paget's disease of bone.

Paget's disease of bone is one of the most common diseases to affect bone, yet it is rare before the age of 50. The etiology of the condition remains unproven. Paget's disease of bone has become less common, less severe, and less extensive in recent decades. Isotope bone scans and radiographs remain the most frequent radiological investigations, demonstrating the extent of the disease and characteristic appearances in most cases. Recent changes in the radiological investigation of Paget's disease include increasing use of computed tomography (CT) and magnetic resonance (MR) imaging for the evaluation of less typical disease or disease complications; the incidental finding of Paget's disease on CT or MR requires recognition to avoid inappropriate investigation. The presence of sclerotic Paget's disease in the lumbar spine or hip may elevate bone mineral density measurements at these sites, with consequent potential to underestimate fracture risk. Awareness of the normal level-to-level vertebral variation in bone density in the spine, and careful assessment of the images acquired on dual energy X ray absorptiometry or quantitative CT will help to avoid this pitfall. Examples of these investigations and the combination of Paget's disease with other conditions such as osteoarthritis, metastatic bone disease, and bone infection are illustrated.