Bone scanning in osteoporosis

This paper reports on bone scanning in osteoporosis a diagnosis of osteoporosis most often follows fracture, and clearly this should be confirmed by x-ray. The bone scan therefore does not have an important role to play in the initial diagnosis of osteoporosis. While the exact mechanism by which the 99mTc-labeled diphosphonates localize in the skeleton is not fully understood, it is believed that they adsorb onto bone surfaces most probably via the calcium of hydroxyapatite crystals. Because the major factors that affect adsorption are osteoblastic activity and to a lesser extent skeletal vascularity, it is apparent that a bone scan image presents a functional display of skeletal metabolic activity. However, osteoporosis is a disorder in which gradual change in bone mass may occur over many years and, in keeping with this minor imbalance in skeletal metabolism, the bone scan appearances are usually normal. However, the scan images may appear of poor quality because of relatively low bone uptake of tracer with, on occasion, a washed-out pattern of activity in the axial and appendicular bone. It has been suggested that such a pattern occurs in severe or end-stage osteoporosis caused by markedly reduced osteoblastic activity. If kyphosis is observed on the bone scan or if there appears to be loss of spinal height with proximity of ribs to each other or increased closeness of rib cage to pelvis, then appearances suggest vertebral collapse and would be in keeping with a diagnosis of osteoporosis. Such evidence is, however, indirect and in practice a bone scan is an extremely unreliable means of diagnosing osteoporosis