Multiple myeloma causes various renal injuries by direct invasion of myeloma cells, AL amyloidosis and hypercalcemia. Hypercalcemia induced by myeloma has been thought to be a result of local osteolysis. Recently, however, it was noted that no significant difference existed in the degree of bone-destruction between hypercalcemic and normocalcemic multiple myeloma. The exact mechanisms of hypercalcemia induced by multiple myeloma remain unconfirmed. In the present study, we report a 70-year-old man, suffering from acute renal failure due to multiple myeloma and severe hypercalcemia. While the serum PTH level was low, PTHrP was markedly increased. Bone scintigraphy implied systemic increase in bone turnover in addition to cold spots corresponding to punched out lesions on bone Xp. After the intravenous administration of bisphosphonate, hypercalcemia and hot accumulation on bone scintigraphy were improved while the PTHrp level and bone destruction by myeloma cells were not improved. The present case suggests involvement of PTHrP in hypercalcemia of multiple myeloma.
