Radiographical and pathological assessment of the activity of Paget's disease of bone

Because specific medication to treat Paget's disease of bone is becoming available, it is important to assess the activity of Paget's disease in order to select appropriate treatment programs for individual patients. Clinical radiographs and pathological specimens demonstrate that specific morphological changes occur in an affected bone over the course of time. In the initial phase osteoclastic resorption of previously existing bone is prominent. Replacement of the normal bone with a type of rapidly remodeled bone is characteristic of the active phase of the disease. Because the new bone may be relatively osteoporotic, collapse of the structure of vertebral bodies is possible. Muscle pull and weight-bearing forces on remodeling cortical bone produces a marked reduction in the numbers of osteoclasts and osteoblasts with the bone marrow reverting to fat cells. The defferentiation between this inactive type of tissue and tissue with active disease is so difficult in routine roentgenograms that reliable evaluation of patients with Paget's disease requires more sensitive methods.