Are children with idiopathic nephrotic syndrome at risk for metabolic bone disease?

BACKGROUND: Children with idiopathic nephrotic syndrome (INS) may be at risk for metabolic bone disease (MBD) because of biochemical derangements caused by the renal disease, as well as steroid therapy. No large study to date has shown conclusively that these children are prone to MBD.

METHODS: We prospectively studied 100 consecutive children with INS for clinical, biochemical, and radiological evidence of MBD. These children were treated with prednisone as follows: initial episode, prednisone, 60 mg/m2/d for 6 weeks, followed by 40 mg/m2 on alternate days for 6 weeks. Relapses were treated with 60 mg/m2/d until remission for 3 days, followed by 40 mg on alternate days for 4 weeks and tapered by 10 mg/m2/wk. Osteoporosis is defined as a bone mineral density (BMD) value evaluated by dual-energy X-linked absorptiometry of the lumbar spine of a z score of 2.5 SDs less than the mean. Univariate and multivariate analyses were performed to analyze for factors predictive of low BMD z score. Children were divided into two groups: those who had received repeated courses of steroid therapy (group II: frequent relapsers (FRs), steroid dependent (SD), or steroid nonresponders (SNRs) versus those who had received infrequent courses (group I: infrequent relapsers).

RESULTS: Twenty-two of 100 children (22%) had osteoporosis. Comparing clinical features, we observed that 6 of 70 children in group II were symptomatic (hypocalcemic signs) compared with none of 30 children in group I (P = 0.10). However, children in group II had significantly lower mean BMD z scores compared with group I (-1.65 +/- 1.35 versus -1.08 +/- 1.0; P = 0.01). Also, 20 of 70 children in group II had osteoporosis compared with 2 of 30 children in group I (P = 0.012). Children in group II had been administered significantly greater doses of steroids compared with group I (P < 0.00001). On multivariate analysis, factors predictive of a low BMD score were older age at onset (P = 0.000), lower total calcium intake (P = 0.000), and greater cumulative steroid dose (P = 0.005).

CONCLUSION: Children with INS are at risk for low bone mass, especially those administered higher doses of steroids (FRs, SD, or SNRs). These children should undergo regular BMD evaluations, and appropriate therapeutic interventions should be planned.