Bone scan in metabolic bone diseases. Review

Metabolic bone disease encompasses a number of disorders that tend to present a generalized involvement of the whole skeleton. The disorders are mostly related to increased bone turnover and increased uptake of radiolabelled diphosphonate. Skeletal uptake of Tc-99m-labelled diphosphonate depends primarily upon osteoblastic activity, and to a lesser extent, skeletal vascularity. A bone scan image therefore presents a functional display of total skeletal metabolism and has valuable role to play in the assessment of patients with metabolic bone disorders. However, the bone scan appearances in metabolic bone disease are often non-specific, and their recognition depends on increased tracer uptake throughout the whole skeleton. It is the presence of local lesions, as in metastatic disease, that makes a bone scan appearance obviously abnormal. In the early stages, there will be difficulty in evaluating the bone scans from many patients with metabolic bone disease. However, in the more severe cases scan appearances can be quite striking and virtually diagnostic.