Multi-organ extraosseous99mTC-HMDP uptake in a case of metastatic melanoma

99mTc-diphosphonates are a class of radiopharmaceuticals, used for bone scintigraphy, able to highlight all lesions characterised by altered osteogenesis. We report the case of a 47-year-old male with an end-stage melanoma, presenting a multi-organ extraosseous activity. Patient underwent whole body scintigraphy using a dual head y-camera, equipped with LEHR collimators. Images were obtained at 3 hours from i.v. injection of 700 MBq of 99mTc-HMDP. Radiochemical purity was 98.2%. The scan showed a decreased skeletal and urinary activity, as well as an intense extraosseous activity in the lungs (especially in the right one), in the stomach, in the liver and a bit lesser in the spleen. Unknown skeletal metastases were also identified. At the time of bone scan, the patient had hypercalcemia and an oliguric acute kidney injury caused by sepsis. Moreover, ultrasound and chest radiography showed the presence of hepatic metastases and radiographic signs of pneumonia in the right lung, respectively. Soft tissues calcifications can be classified in two groups: metastatic calcifications, where calcium sediments in normal tissues, and dystrophic calcifications, where this deposit occurs only in previously injured organs. Metastatic calcifications mainly occur in patients in hemodialytic treatment, since the hyperparathyroism and the acidosis, due to the interdialytic interval, induce an hypercalcemia. Moreover, the reduced glomerular filtration causes hyperphosphatemia and, consequently, increased calcium-phosphate products. On the other hand, dystrophic calcifications occur in injured tissues, even without increased serum calcium levels. Our patient had high levels of calcemia, but not a secondary hyperparathyroidism, so other causes must be researched. It's common knowledge that a high level of calcemia can be found in 10 to 20% of cases with advanced cancer. Indeed, the patient had bone metastases and malignant hypercalcemia. The 99mTc-HMDP uptake was different in the two lungs, with a greater intensity in the right one. This pattern is probably due to two causes: hypercalcemia (linked to the end-stage cancer), that explains the bilateral lungs uptake, and an injured tissue, for example in presence of an infection, that generates a greater uptake in the right lung. The increased uptake of 99mTc-HMDP in other patient's organs was probably due to some of mechanisms already involved in pulmonary calcifications. Moreover hepatic image showed a patchy activity, with some areas of more evident calcifications, probably due to the presence of malignant metastases. Malignant hypercalcemia depends on several causes, like the osteoclastic bone resorption and the secretion of parathyroid hormone related protein (PTHrP), and may be associated with extra-skeletal images at bone scintigraphy. A previous oxidant injury can contribute to more intense calcifications in the involved tissues.