Bone alterations in patients with idiopathic hypercalciuria and calcium nephrolithiasis.

OBJECTIVES: To verify whether alterations in bone density and turnover in patients with calcium nephrolithiasis and hypercalciuria are observable in various subgroups of patients divided according to the pathogenesis of the hypercalciuria.
METHODS: Seventy patients with calcium nephrolithiasis and idiopathic hypercalciuria, 19 to 64 years old, were assessed for spine and femur mineral metabolism and bone density using a Dexa evaluation system. After a low calcium diet, the subjects were classified into two groups: fasting hypercalciuria (FH, 39 patients) and absorptive hypercalciuria (AH, 31 patients).
RESULTS: Only in the patients with FH was the lumbar spine bone density lower than in the controls (P <0.001). Also, only the patients with FH had higher bone alkaline phosphatase and urinary hydroxyproline levels than the control group (P <0.005 and <0.015, respectively). The blood pH levels were lower, even though within the normal range, in the hypercalciuric patients than in the controls (P <0.01). There was a negative correlation between the urinary hydroxyproline level and lumbar spine and femoral neck density in patients with FH (P <0.001 and <0.005, respectively), and the blood pH correlated positively with the lumbar spine bone density.
CONCLUSIONS: Altered bone metabolism and overall bone loss were found only in the patients with FH. Overloading of acid valences, perhaps of dietary origin, could be the pathogenic factor responsible.