What is the etiology and pathophysiology of Idiopathic Hypercalciuria?
- IH affects 10% of the general population and 40% of stone formers. The four types of IH are AH-I, AH-II, AH-III, and RH.
- AH-I and AH-II result from increased intestinal sensitivity to calcitriol with intestinal calcium hyperabsorption and higher numbers of vitamin D receptors in osteoblasts, causing greater bone resorption and resorptive hypercalciuria.
- The latter accounts for decreased bone mass seen in many patients with AH-I and in some of those with AH-II. AH-III, an unusual disorder, is caused by a renal phosphate leak with urinary loss of phosphate, decreased serum phosphate, and increases in renal calcitriol production and intestinal calcium absorption.
- The level of the phosphaturic factor, fibroblast growth factor 23 (FGF23), is increased in some patients with calcium nephrolithiasis, hypophosphatemia, and renal phosphate leak.
- RH is characterized by impaired tubular reabsorption of calcium, which causes a decrease in serum calcium, elevations in PTH and calcitriol, and increases in bone resorption and intestinal calcium absorption.
