Low bone mass in idiopathic renal stone formers: Magnitude and significance

Abstract To assess bone mineral density (BMD) in idiopathic calcium nephrolithiasis, dual-energy x-ray absorptiometry was performed at lumbar spine, upper femur (femoral neck, Ward's triangle, and total area), distal tibial diaphysis, and distal tibial epiphysis in 110 male idiopathic calcium stone formers (ICSF); 49 with and 61 without hypercalciuria on free-choice diet). Results were compared with those obtained in 234 healthy male controls, using (1) noncorrected BMD, (2) BMD corrected for age, height, and BMI, and (3) a skeletal score based on a tercile distribution of BMD values at following four sites: lumbar spine, Ward's triangle, tibial diaphysis, and tibial epiphysis. After correction, BMD—and therefore also skeletal score—tended to be lower in the stone formers than in controls at five of the six measurement sites, that is, lumbar spine, upper femur, Ward's triangle, tibial diaphysis, and tibial epiphysis, limit of significance being reached for the last two sites without difference between hypercalciuric (HCSF) and normocalciuric stone formers (NCSF). Estimated current daily calcium intake was significantly lower in patients (616 + 499 mg/24 h, mean + SEM) than in controls (773 + 532, p = 0.02). Of 17 patients who in the past had received a low-calcium diet for at least 1 year, 10 had a low skeletal score (4-6) whereas only 1 had a high score (10-12; p = 0.037). Of the 12 stone formers in the study with skeletal score 4 (i.e., the lowest), 8 had experienced in the past one or more fractures of any kind versus only 19 of the remaining 77 patients with skeletal score 5-12 (p = 0.01). Significant correlations were found between corrected BMD at various sites and 24 h sulfate, uric acid and sodium excretion, and urinary pH, as well as serum uric acid concentration. BMD at tibial diaphysis was negatively correlated with pyridinoline/ creatinine concentration ratio in 24 h urine samples, and skeletal score was negatively correlated with fasting hydroxyprolinuria. In summary, there is a slight decrease in skeletal mineral content in idiopathic calcium stone formers at the tibial site that appears to be related at least in part to dietary habits (low-calcium diet and animal protein and sodium intake) experienced by these patients.