Findings: Whole body images in anterior and posterior projections were obtained three hours after intravenous injection of approximately 30 mCi of Tc-99m-MDP. Images demonstrated additional abnormally increased uptake of radiopharmaceutical activity in the spine, skull, ribs, humeri, femurs, and pelvis. Multiple additional foci of abnormal uptake were seen compared to previous images.

Diagnosis: Diffuse skeletal metastases from prostate cancer.

Discussion: The most common use of the bone scan is for the detection and monitoring of metastatic tumor involving the skeleton. The tumors monitored include prostate, lung, breast, thyroid, and renal carcinoma among many others. The majority of metastases afflict the axial skeleton in a pattern that reflects the distribution of the erythropoietic marrow. Comparison bone scans at intervals of 3-6 months allow an accurate assessment of tumor spread. Merely counting the hot spots is of little value in the management of oncologic problems. Increased numbers and size of individual lesions usually indicates that the tumor load of the skeleton is expanding. Increased intensity of the individual lesions (in the absence of new lesions) frequently means that the tumor has become static and that the osteoblasts around it are engaged in vigorous repair. This "flare" response is usually a good indicator that a tumor has been checked by therapy.

Usually, Tc-99m-MDP, gets normally excreted by the kidneys. This scan shows numerous prostate cancer metastases produces "hot" spots of intense isotope accumulation that leave little or none of the radiopharmaceutical for renal excretion. In such cases, the bone scan is referred to as a "superscan."

References:
McNeil BJ. Values of bone scanning in neoplastic disease. Semin Nucl Med 1984; 14:277-286.

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