LOW BONE MASS IN IDIOPATHIC RENAL STONE FORMERS - MAGNITUDE AND SIGNIFICANCE

To assess bone mineral density (BMD) in idiopathic calcium nephrolithi asis, dual-energy x-ray absorptiometry was performed at lumbar spine, upper femur (femoral neck, Ward's triangle, and total area), distal ti bial diaphysis, and distal tibial epiphysis in 110 male idiopathic cal cium stone formers (ICSF); 49 with and 61 without hypercalciuria on fr ee-choice diet). Results were compared with those obtained in 234 heal thy male controls, using (1) noncorrected BMD, (2) BMD corrected for a ge, height, and BMI, and (3) a skeletal score based on a tercile distr ibution of BMD values at following four sites: lumbar spine, Ward's tr iangle, tibial diaphysis, and tibial epiphysis. After correction, BMD- and therefore also skeletal score-tended to be lower in the stone form ers than in controls at five of the six measurement sites, that is, lu mbar 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 s tone formers (NCSF). Estimated current daily calcium intake was signif icantly 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 r eceived 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 ver sus only 19 of the remaining 77 patients with skeletal score 5-12 (p = 0.01). Significant correlations were found between corrected BMD at v arious sites and 24 h sulfate, uric acid and sodium excretion, and uri nary pH, as well as serum uric acid concentration. BMD at tibial diaph ysis was negatively correlated with pyridinoline/creatinine concentrat ion ratio in 24 h urine samples, and skeletal score was negatively cor related with fasting hydroxyproliruria. In summary, there is a slight decrease in skeletal mineral content in idiopathic calcium stone forme rs at the tibial site that appears to be related at least in part to d ietary habits (low-calcium diet and animal protein and sodium intake) experienced by these patients.