An Insight Into the Pathogenesis of Hypercalciuria

Hypercalciuria with or without hypercalcemia is a well-known complication of sarcoidosis, the patho- genesis of which is not fully understood. Pregnancy is associated with physiologic alterations in calcium metabolism. These changes can further alter the derangement of calcium metabolism that occurs in sarcoidosis, if the two conditions coexist. We had the opportunity to study prospectively the changes in serum and urine calcium along with all the hormonal changes that occur during pregnancy in a young woman with sarcoidosis, who had hypercalciuria at presentation. We believe that an increased level of calcitriol is central to the calcium abnormalities in our patient. In her case, the increased calcitriol is derived from sarcoid granulomas and renal sources enhanced by the effect of estradiol and prolactin on the conversion of 25(OH)D to 1,25(OH)2 D. She acquired hypoparathyroidism, with normal serum calcium, which probably was due to the direct sup- pression of parathyroid hormone (PTH) secretion by calcitriol. Finally, hypercalciuria is the result of the combined effect of hyperabsorption of calcium from the gut (the result of increased calcitriol levels lead- ing to increased filtration of calcium) and decreased tubular reabsorption of calcium, as a result of unde- tectable PTH. (CHEST 2004; 126:995-998)