[Osteoporosis in a man with idiopathic hypercalciuria, renal variety, treated with a hypocalcic diet]

A 61 year old man with a calcic urinary stone at age 46 was submitted to a prolonged low calcium diet (about 400 mg/day). Normal serum calcium and elevated urinary Ca (725 mg/day were demonstrated). After a diet with a normal Ca content (900 mg/day) urinary excretion did not change. PTH, serum Ca and P were normal. Biphoton bone densitometry revealed severe osteopenia, with a spine density of 51% of normal. The addition of hydrocortisone (50 mg/day) reduced urinary Ca output over 25%; the addition of phosphate, 1125 mg/day, brought Ca output to normal levels. Thus, prolonged dietary restriction of Ca in the presence of high urinary Ca loss may produce severe osteopenia and osteoporosis.