Recent advances and controversies in childhood renal osteodystrophy

Minimizing bone abnormalities in children with renal failure

Renal osteodystrophy (ROD), a metabolic bone disease accompanying chronic renal failure (CRF), is a major clinical problem in pediatric nephrology. Growing and rapidly remodeling skeletal systems are particularly susceptible to the metabolic and endocrine disturbances in CRF. The pathogenesis of ROD is complex and multifactorial. Hypocalcemia, phosphate retention, and low levels of 1,25 dihydroxyvitamin D(3) related to CRF result in disturbances of bone metabolism and ROD. Delayed diagnosis and treatment of bone lesions might result in severe disability. Based on microscopic findings, renal bone disease is classified into two main categories: high- and low-turnover bone disease. High-turnover bone disease is associated with moderate and severe hyperparathyroidism. Low-turnover bone disease includes osteomalacia and adynamic bone disease. The treatment of ROD involves controlling serum calcium and phosphate levels, and preventing parathyroid gland hyperplasia and extraskeletal calcifications. Serum calcium and phosphorus levels should be kept within the normal range. The calcium-phosphorus product has to be <5 mmol(2)/L(2) (60 mg(2)/dL(2)). Parathyroid hormone (PTH) levels in children with CRF should be within the normal range, but in children with end-stage renal disease PTH levels should be two to three times the upper limit of the normal range. Drug treatment includes intestinal phosphate binding agents and active vitamin D metabolites. Phosphate binders should be administered with each meal. Calcium carbonate is the most widely used intestinal phosphate binder. In children with hypercalcemic episodes, sevelamer, a synthetic phosphate binder, should be introduced. In children with CRF, ergocalciferol (vitamin D(2)), colecalciferol (vitamin D(3)), and calcifediol (25-hydroxyvitamin D(3)) should be used as vitamin D analogs. In children undergoing dialysis, active vitamin D metabolites alfacalcidol (1alpha-hydroxy-vitamin D(3)) and calcitriol (1,25 dihydroxyvitamin D(3)) are applied. In recent years, a number of new drugs have emerged that hold promise for a more effective treatment of bone lesions in CRF. This review describes the current approach to the diagnosis and treament of ROD.

Renal osteodystrophy in dialysis patients: diagnosis and treatment

This article reviews the clinical, biological, radiological, and pathological procedures and their respective indications for the practical diagnosis of the following various histological patterns of renal osteodystrophy: osteitis fibrosa due to parathyroid hormone (PTH) hypersecretion: osteomalacia or rickets due to native vitamin D deficiency and/or aluminum overload; and adynamic bone disease (ABD) due to aluminum overload and/or PTH secretion oversuppression. Our advice regarding bone biopsy is to restrict it to patients with symptoms and hypercalcemia, especially those who have been previously exposed to aluminum. In other cases, we propose relying merely on the determination of the plasma concentrations of calcium, protide, phosphate, bicarbonate, intact PTH, aluminum, 25(OH)D3, and alkaline phosphatase (total and bony if hepatic disease is associated) to choose the appropriate treatment. Because of the danger of the desferrioxamine treatment necessary to chelate and remove aluminum, the suspicion of aluminic bone disease (osteomalacia or ABD) will always be confirmed by a bone biopsy. In the case of nonaluminic osteomalacia, correction of the vitamin D deficiency by native vitamin D or 25(OH)D3, and of the calcium deficiency and acidosis by alkaline salts of calcium and if necessary sodium bicarbonate are sufficient to cure the disease. In the case of nonaluminic ABD, the stimulation of PTH secretion by the discontinuation of 1alpha hydroxylated vitamin D and the induction of a negative calcium balance during dialysis by decreasing the calcium concentration in the dialysate will allow an increase of the CaCO3 dose to correct for hyperphosphatemia without inducing hypercalcemia. For hyperparathyroidism, i.e., plasma intact PTH levels greater than two- or four-fold the upper limit of normal levels (according to the absence or presence of previous aluminum exposure), the treatment will consist in increasing the CaCO3 dose to correct for hyperphosphatemia together with a decrease of the calcium concentration in the dialysate if the dose of CaCO3 is so high that it induces hypercalcemia. When the hyperphosphatemia has been corrected and there is still a low or normal corrected plasma calcium level, 1alpha(OH)D3 in an oral bolus 2 or 3 times a week should be given at the minimal dose of 1 microg. When the PTH level stays above 400 pg while hypercalcemia occurs and hyperphosphatemia persists, surgical subtotal parathyroidectomy is recommended or the injection of calcitriol into the big nodular hyperplastic parathyroid glands under sonography control in high surgical risk patients. Special recommendations are given for children.

Growth charts for prepubertal children with chronic renal failure due to congenital renal disorders. European Study Group for Nutritional Treatment of Chronic Renal Failure in Childhood

Despite the high prevalence of and therapeutic attention to growth failure in children with chronic renal failure (CRF), systematic evaluations of spontaneous growth in CRF are lacking. Therefore, we collected retrospectively longitudinal growth and biochemical data in 321 prepubertal patients treated for CRF due to congenital renal disorders. Data were recorded at 3-month intervals during the first 2 years of life and 6-monthly thereafter, up to the age of 10 years. Around 100 measurements were available per age interval. Mixed-longitudinal percentile curves of height and height velocity were constructed. Moreover, a statistical comparison with the heights and height velocities of healthy children and an evaluation of the effect of biochemical parameters on growth was performed. The CRF children had normal heights at birth but dropped below the 3rd normal percentile during the first 15 months of life. Thereafter, growth patterns usually were percentile parallel, with a mean height standard deviation score (SDS) of -2.37 +/- 1.6. Height velocities were consistently lower in patients with glomerular filtration rates (GFRs) below one-third of the lower normal limit (25 ml/min per 1.73 m2 for patients > 1 year) than in patients with better renal function. This difference in growth rates resulted in a mean height SDS of -1.65 +/- 1.5 SDS and -2.79 +/- 1.4 SDS (age 1-10 years) in the subgroups with relatively better and worse GFR, respectively. Regression analysis confirmed that GFR was a weak but significant predictor of height velocity SDS in most age groups.

Alphacalcidol oral pulses normalize uremic hyperparathyroidism prior to dialysis

Alphacalcidol oral pulse therapy was given for secondary hyperparathyroidism to 22 children (mean age of 5.6 years) with renal insufficiency. At the beginning of the study, the glomerular filtration rate was < 50% of normal, serum intact parathyroid hormone (PTH) was > 100 ng/l and the serum phosphate and calcium concentrations were within the normal range. Alphacalcidol (0.5-3.0 micrograms) was given orally thrice weekly in the evening and adjusted according to PTH, ionized calcium and phosphate concentrations. Serum PTH (mean +/- SEM) decreased significantly from a pre-treatment level of 393 +/- 81 ng/l to 122 +/- 34 ng/l after 12 months, and stabilized at this level. Mean vitamin D metabolite concentrations were within the normal range. 1,25-Dihydroxyvitamin D did not increase during therapy, while PTH decreased. The estimated creatinine clearance remained almost unchanged (20 +/- 3 and 21 +/- 6 ml/min per 1.73 m2). Growth remained low normal (height standard deviation score -1.8 +/- 0.3 initially and -1.7 +/- 0.4 12 months later) and bone mineral density did not decrease. We concluded that feedback regulation of PTH with oral alphacalcidol pulse therapy is effective in the treatment of hyperparathyroidism in children with renal failure prior to dialysis.

Intramuscular calcitriol for uraemic children with severe hyperparathyroidism and hypercalcaemia

The effect of intramuscular calcitriol was evaluated in five children (aged 1-16 years) with severe chronic renal failure and hyperparathyroidism [range of intact parathyroid hormone (PTH) 400-1,200 pg/ml]. All five children had been on oral calcitriol or 1 alpha-hydroxyvitamin D3 treatment (5-20 ng/kg per day), but an adequate, efficacious dosage could not be achieved since any attempt of increasing the dosage resulted in severe hypercalcaemia (> 2.9 mmol/l). Intramuscular calcitriol was given three times weekly for 5 months at an initial dosage of 65-70 ng/kg to all but one patient who received 100 ng/kg. In the first three patients, treatment resulted in an 86%-98% fall in serum PTH compared with baseline levels and serum calcium never exceeded 2.65 mmol/l, except for one episode of hypercalcaemia in one patient. In the last two patients, serum calcium rose above normal limits, thus calcitriol had to be discontinued several times and then restarted at a lower dosage (40 ng/kg); PTH fell by 61% and 73%, respectively, compared with basal values. All patients had very low pre-treatment levels of serum 1,25-dihydroxyvitamin D3 (5-15 pg/ml) which were normalized (35-56 pg/ml) by the intramuscular calcitriol-treatment. Serum phosphorus and magnesium did not vary in any of the five patients. No side effects were observed at the injection site. Intramuscular calcitriol seems a useful therapeutic option for patients with severe hyperparathyroidism associated with a high serum calcium level when treated with conventional oral calcitriol.

Evaluation of lumbar bone mineral density by dual energy x-ray absorptiometry

Using dual-energy x-ray absorptiometry (DEXA), the lumbar spinal bone mineral density (BMD) in 49 Japanese children with or without metabolic bone disease (MBD) was determined. The following results were obtained: (a) The normal data for healthy Caucasians (J Clin Endocrinol Metab 1990; 70: 1330-1333) appear to be applicable to Japanese children; (b) BMD was normal in patients with congenital hydronephrosis with normal renal function; (c) One patient with congenital renal failure and one with Lowe syndrome had low BMD, but the MBD in the former improved markedly with peritoneal dialysis; (d) A reduced BMD was found in patients treated with long-term steroids, probably because of decreased turnover of bone; (e) A reduction in BMD was pronounced in preterm infants during the first few months of life. In conclusion, DEXA is a useful method of bone densitometry in MBD in children.

Renal osteodystrophy in patients on continuous ambulatory peritoneal dialysis

Twelve patients on continuous ambulatory peritoneal dialysis (CAPD) were studied in order to evaluate the progression of renal osteodystrophy (ROD). All patients received doses of 0.01-0.02 microgram/kg of 1 alpha vitamin D3 (1 alpha-D3) and 0.1-0.15 g/kg of calcium carbonate for 12-18 months. Serum total protein, total calcium (Ca), creatinine, inorganic phosphate, alkaline phosphatase (ALP), and n-terminal parathyroid hormone were measured regularly. The radiological bone appearance for ROD or rickets and the height standard deviation score were compared between the outset and the end of this study. An increase of Ca values and a decrease of ALP values correlated with a suppression of hyperparathyroidism, and the hyperphosphatemia was controlled in the majority of our patients throughout this study. Two patients had ROD and rickets at the outset of this study, and all patients but one had neither ROD nor rickets at the end of this study. Growth retardation improved or remained stable in 10 patients. Our results indicate that adequate doses of 1 alpha-D3 and calcium carbonate are effective in the prevention of ROD and rickets in patients on CAPD.