Tetany due to hypomagnesemia induced by cisplatin and doxorubicin treatment for synovial sarcoma

Hypocalcemic crisis developed in a patient with monophasic synovial sarcoma after amputation of the right leg, followed by long-term treatment with cisplatin and doxorubicin. Laboratory data revealed severe hypomagnesemia and hypocalcemia. High normal intact parathyroid hormone (PTH), elevated mid-region PTH and undetectable osteocalcin levels had already been found before the appearance of obvious symptoms concomitantly associated with moderate hypomagnesemia and hypocalcemia. Further, both PTH levels measured by two different methods gradually decreased until the initiation of magnesium supplementation. The magnesium supplement immediately relieved the tetany, and induced striking increases in both intact and mid-region PTH levels transiently and continuous elevations of osteocalcin levels. These results suggest that magnesium depletion has dual effects on PTH secretion, from stimulation to inhibition, as hypomagnesemia progresses. Both relative hypoparathyroidism and refractoriness of bone to PTH were thought to be responsible for hypocalcemia due to hypomagnesemia.