Primary hyperparathyroidism and idiopathic hypercalciuria.

Primary hyperparathyroidism and idiopathic hypercalciuria are important causes of calcium stone disease. Hypercalcemia is usually the clue to the presence of primary hyperparathyroidism, but a minority of patients are intermittently or persistently normocalcemic. In these patients there appears to be a resistance to the effect of parathyroid hormone on renal calcium transport, to which calcitriol may contribute. Such patients mimic those with idiopathic hypercalciuria, the commonest metabolic cause of stone formation. The pathophysiology of idiopathic hypercalciuria remains controversial, but abnormalities of renal tubule function and disordered vitamin D metabolism are commonly present. The separation into so-called renal and absorptive types does not appear to be of practical importance, since thiazide diuretics provide effective prophylaxis regardless of type.