Can the three-phase bone scan differentiate osteomyelitis from metabolic or metastatic bone disease?

The three-phase bone scan has been reported of value in the diagnosis of osteomyelitis. The use of a radionuclide angiogram, an immediate postinjection "blood pool" image, and 2 to 3 hour delayed image have been useful in separating nonosseous inflammatory disease from osteomyelitis. However, dependence on increased blood flow and focal hyperemia for this diagnosis may limit the use of the study if other processes are shown to produce similar results. To identify limitations of the three-phase bone scan we studied 14 patients with metastatic bone disease and nine patients with Paget's disease. Blood flow results showed no increase in three of 14 patients with metastases, intermediate increase in seven of 14 patients with metastases and two of nine patients with Paget's, and intense increase in four of 14 patients with metastases and seven of nine patients with Paget's. All patients showed increased focal activity in the immediate "blood pool" and delayed images. We conclude that because of increased flow Paget's disease may be difficult to separate from osteomyelitis. However, metastatic disease can often be differentiated on the basis of quantitative focal hyperemia. The three-phase bone scan remains of value in the diagnosis of osteomyelitis, but other diseases of bone must be included in the differential diagnosis.