Contributory metabolic factors in the development of nephrolithiasis in patients with medullary sponge kidney

Whether specific metabolic abnormalities are related to nephrolithiasis in patients with medullary sponge kidney (MSK) remains a debated issue. The pu rpose of this study is to determine metabolic disorders in patients with MS K and nephrolithiasis compared with idiopathic calcium-stone-forming patien ts. One hundred eighty-four patients with recurrent calcium-stone formation s were investigated with regard to metabolic abnormalities, Of these, 22 pa tients (11.9%; 13 men, 9 women) showed MSK by radiological examination. MSK was defined as a kidney that presented at least three linear or round papi llary opacities in the affected papilla on urography, Multiple stones (more than five) existed in both kidneys in all patients with MSK. The remaining 162 patients (109 men, 53 women) were idiopathic calcium-stone formers. Fr equencies of low urine volume (urine < 1,500 mL/24 h) and hyperoxaluria (ox alate > 40 mg/24 h) were similar between the groups. Hypercalciuria (men, c alcium a 300 mg/24 h; women, calcium of 250 mg/24 h) was found less frequen tly in the MSK group. The frequency of hypocitraturia (citrate < 300 mg/24 h) was significantly greater in the MSK group than the idiopathic group (77 .3% versus 33.9%, respectively). Mean 24-hour urinary excretions of calcium , citrate, uric acid, and magnesium were significantly less in the MSK grou p. No differences were found in serum calcium, phosphate, and parathyroid h ormone levels between the groups. Low urinary excretions of citrate and mag nesium are the most typical metabolic disorders that distinguish MSK stone patients from idiopathic calcium-stone-forming patients. In addition to suc h anatomic abnormalities as ectatic collecting ducts, low levels of urinary inhibitors of stones seem to contribute to the pathogenesis of nephrolithi asis in patients with MSK. (C) 2001 by the National Kidney Foundation, Inc.