Renal osteodystrophy in children undergoing continuous ambulatory peritoneal dialysis

Renal Osteodystrophy and the Status of Aluminum and Other Trace Metals in CAPD Patients: A Panel Review

Most reports indicate that in patients on CAPD, hyperparathyroid bone disease progresses, while osteomalacia improves. With 1.5g% Dianeal, and when dialysate Ca is 7mg%, peritoneal mass transfer of calcium is positive, i.e., it is absorbed from the solution, while with hypertonic solutions it is less positive or even negative. Daily phosphorus removal by CAPD is insufficient to control serum phosphorus, hence CAPD patients require phosphate binders and/or phosphate restriction. Peritoneal phosphorus removal is greater with hypertonic than with isotonic solutions.

In patients on CAPD, the loss of substantial amounts of D-binding protein and 25(OH)DJ into the dialysate, produces a gradual decrease in plasma 25(OH)D levels. Similarly, these patients have low 1,25(OH)D2 DJ levels and, hence, should receive vitamin D or its analogues.

Unlike hemodialysis, CAPD results in a significant removal of PTH, with a peritoneal clearance of 1.5 ml/min. However, despite an estimated daily loss of 13.5% of the circulating PTH, there probably is not a significant effect on plasma PTH levels, which usually respond to changes in serum Ca. Levels of the intact PTH molecule provide a better index of hyperparathyroidism than do levels of its COOH-terminal fragment.

With regard to investigation and treatment, one should measure serum ionic calcium rather than total calcium, even if the latter is corrected for total protein. The minimal dialysate calcium should be 7 mg/dl and for hypertonic solutions, perhaps it should be higher (7.5–8.0 mg%). Total serum calcium should be maintained at 10.2–10.7 mg/dl (ionized calcium of 5.1–5.5 mg/dl); adjunctive use of active forms of vitamin D and prevention of aluminum intoxication may prevent progressive bone disease in CAPD, and existing bone disease may heal.

Whereas there are enough data supporting the connection of aluminum toxicity and osteomalacia in hemodialysis patients, data concerning the incidence of osteomalacia and its relationship to aluminum in CAPD patients are scarce. Apparently CAPD removes aluminum more efficiently than hemodialysis. CAPD patients are less likely to develop osteomalacia because the dialysate aluminum content is low and these patients tend to require lower doses of phosphate binder.

There are no extensive studies on trace element deficiencies or excess in patients on CAPD. These patients may be more susceptible to deficiencies of trace elements which are protein bound. Desferoxamine may be effectively used for the treatment of patients with either aluminum or iron overload.

Secondary hyperparathyroidism in children with chronic renal failure: pathogenesis and treatment

Despite advances in the management of patients with chronic renal failure, histologic features associated with secondary hyperparathyroidism remain the predominant skeletal findings; however, over the last decade the prevalence of adynamic bone has increased in both adult and pediatric patients with chronic renal failure. The management of children with secondary hyperparathyroidism and mild to moderate chronic renal failure should be started early, and should include correction of hypocalcemia and metabolic acidosis, maintenance of age-appropriate serum phosphorus levels, and institution of vitamin D therapy when serum intact parathyroid hormone (PTH) measurements are elevated to maintain the blood levels within normal limits; however, in children undergoing chronic dialysis therapy, the current recommendation is to maintain the serum intact PTH levels at least 2-4 times the upper limits of normal to prevent the development of low bone turnover disease. Serum calcium, phosphorus, alkaline phosphatase, and PTH levels should be monitored frequently, especially in infants and very young children. Discontinuation or reduction of vitamin D should be considered when there is a rapid decline in PTH levels, persistent elevation in serum calcium and serum phosphorus levels, and a significant diminution in alkaline phosphatase levels. In addition, a reduction in the calcium concentration of the dialysis fluid, and judicious use of calcium-containing salts as phosphate binding agents should also be performed in these patients. Although not yet extensively used in pediatric patients with secondary hyperparathyroidism, several therapeutic alternatives, such as the less calcemic vitamin D analogs, including paricalcitol [19-nor-1,25-(OH)(2)D(2)] and doxercalciferol [1-alpha-(OH)(2)D(2)], calcimimetics, and the availability of a calcium-free, aluminum-free phosphate binder such as sevelamer hydrochloride and lanthanum carbonate, may play significant roles in the future management of children with secondary hyperparathyroidism to promote linear growth, prevent parathyroid gland hyperplasia, avoid calciphylaxis and, in the long run, avert vascular calcifications.

Evaluation of vitamin D-binding protein and vitamin D metabolite loss in children on continuous ambulatory peritoneal dialysis

We measured the serum concentration of vitamin D-binding protein (DBP) in children with chronic renal failure (CRF). We also evaluated the relationships between the peritoneal loss of vitamin D metabolites, DBP and albumin in nine children on continuous ambulatory peritoneal dialysis (CAPD). The serum levels of DBP in children with CRF were significantly higher than in normal children. The mean serum DBP level in CRF children undergoing CAPD was slightly lower than in CRF patients who were not on dialysis. In patients on CAPD, the peritoneal loss of 25-hydroxyvitamin D (25OHD) showed a significant positive correlation with the DBP concentration in the dialysate (r = 0.855, P less than 0.005). In contrast, the peritoneal loss of 1,25-dihydroxyvitamin D (1,25(OH)2D) showed a significant correlation with the loss of albumin in the dialysate (r = 0.779, P less than 0.01). The synthesis of 1,25(OH)2D3 is reduced in advanced renal failure, and the peritoneal losses of the active vitamin D sterols in patients on CAPD may aggravate this deficiency. We recommend that supplementation of active form of vitamin D, such as 1 alpha-hydroxyvitamin D3 or 1,25(OH)2D3, is important in CAPD patients, particularly those with elevated peritoneal loss of DBP and/or albumin.

Pharmacokinetics of calcitriol in continuous ambulatory and cycling peritoneal dialysis patients

Oral calcitriol is commonly used for the treatment of secondary hyperparathyroidism in patients undergoing long-term dialysis, but it has been suggested that intravenous (IV) or intraperitoneal (IP) administration enhances the therapeutic efficacy of the sterol. To examine potential mechanisms for this difference, the bioavailability of calcitriol was evaluated after single oral (PO), IV, and IP doses of 60 ng/kg in each of six adolescent patients with osteitis fibrosa undergoing continuous ambulatory peritoneal dialysis (CAPD) or continuous cycling peritoneal dialysis (CCPD). Serum calcitriol levels were 3.6 +/- 4.3, 8.2 +/- 7.5, and 2.5 +/- 3.0 pg/mL, respectively, before IV, PO, and IP doses of the sterol; these values increased to similar levels at 24 hours: 55.6 +/- 14.6 pg/mL after PO, 56.4 +/- 17.6 pg/mL after IV, and 53.8 +/- 20.1 pg/mL after IP. Serum calcitriol levels were higher 1, 3, and 6 hours after IV injections than after PO or IP doses; values thereafter did not differ among groups. The bioavailability of calcitriol, determined from the 24-hour area under the curve (AUC0-24) for the increase in serum calcitriol concentration above baseline values was 50% to 60% greater after IV, 2,340 +/- 523 pg.mL-1.h-1, than after PO, 1,442 +/- 467 pg.mL-1.h-1, or IP, 1,562 +/- 477 pg.mL-1.h1, dosages, P less than 0.05. These differences were due to higher values for AUC during the first 6 hours after calcitriol administration. Although IP calcitriol did not increase sterol bioavailability, radioisotope tracer studies indicated that 35% to 40% of the hormone adheres to plastic components of the peritoneal dialysate delivery system.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Descriptions of the participating centers and patient population in the Growth Failure in Children with Renal Diseases Study

The Growth Failure in Children With Renal Diseases Study, a double-blind, multicenter clinical trial with 108 children entered into the control period over 4.3 years of patient enrollment (December 1984 to April 1989), is being extended for 3 years (December 1988 to December 1991) to provide the time needed to accrue additional patients, aged between 1 1/2 and 10 years, with glomerular filtration rates of 20 to 75 ml/min/1.73 m2. The study design of randomization to two treatment arms (1,25-dihydroxyvitamin D vs dihydrotachysterol) requires a total of 108 patients with a minimum of 6 months of treatment to test the long-term effectiveness and safety of 1,25-dihydroxyvitamin D, an essential part of the therapeutic regimen for children with chronic renal insufficiency. The frequent longitudinal assessments of nutrition and growth in children with chronic renal insufficiency can better define the natural history of renal disease and its influence on growth. Similar data in the treatment period will define the impact of treatment with 1,25-dihydroxyvitamin D3 versus dihydrotachysterol on this natural history. Linear growth must be observed long enough (6 to 12 months minimum) to permit valid quantitation and comparison of the two vitamin D treatment arms, the multiple confounding variables that affect growth (e.g., steroid therapy, diabetes mellitus, prior vitamin D treatment) must be rigorously excluded or controlled, and the assignment of patients to the two groups must be random. These controls--sufficient study duration, sufficient patient numbers, and randomization--should eliminate extraneous sources of variation, including seasonal periodicity. This carefully developed, double-blind clinical trial with multiple participating centers and an effective organizational structure is coming close to achieving the goals of the study. An explosion of data regarding the natural history of chronic renal insufficiency and its treatment with vitamin D metabolites will be forthcoming at the conclusion of the study.

Bone disease in pediatric patients undergoing dialysis with CAPD or CCPD

The histologic features of renal osteodystrophy and the prevalence of bone aluminum deposition in children receiving regular dialysis have not been described. Forty-four pediatric patients undergoing continuous ambulatory (CAPD) or cycling (CCPD) peritoneal dialysis had bone biopsies and deferoxamine (DFO) infusion tests; all were receiving oral calcitriol. Osteitis fibrosa (OF) was found in 39%, mild lesions (M) in 25%, normal histology (NH) in 16%, aplastic lesions (AP) in 11%, and osteomalacia (OM) in 9%. Bone surface aluminum (SA) was present by histochemical staining in 10 out of 20 given aluminum-containing phosphate-binding agents and in 0 of 24 treated with calcium carbonate; chi 2 = 15.5, P less than 0.0001. Serum biochemistries and DFO infusion tests failed to predict bone histology, but plasma aluminum levels were markedly elevated and bone aluminum content was highest in patients with OM. Bone formation rate (BFR) correlated with serum parathyroid hormone (PTH), r = 0.55, P less than 0.001; BFR was inversely related to bone aluminum content (r = -0.42, P less than 0.01), even in patients with OF (r = -0.66, P less than 0.05). All patients with SA greater than 30% had normal or reduced BFR when compared to those with SA less than 30%; chi 2 = 12.2, P less than 0.005. Based on SA greater than 30%, six patients were classified as aluminum-related bone disease: three OM, one AP, and two NH. Two-thirds of pediatric patients undergoing CAPD/CCPD have persistent hyperparathyroidism despite treatment with calcitriol, but aluminum can adversely affect BFR when SA exceeds 30% regardless of histologic lesion or serum PTH level.

Renal osteodystrophy

Over the past decade important advances in our understanding of the pathophysiology and treatment of renal osteodystrophy have been made. In particular, the role of calcitriol deficiency in the genesis of hyperparathyroidism in early renal failure is now better understood. So too are the effects of aluminium on bone, and whereas the more florid aluminium related disease is now unusual the more subtle effects of aluminium are now being appreciated. There is still a major problem in the long-term treatment of hyperparathyroid bone disease. The reasons why parathyroid gland proliferation continues to occur on dialysis therapy require a better understanding of cellular events regulating hormone production and parathyroid cell replication. The case for early intervention with vitamin D is now strong but whether such an approach materially influences the long-term outcome is not yet established. Changes in the approach to treatment and in the modalities used for renal replacement therapy will continue to modify the nature of the bone disease.

"High-dose" calcitriol for control of renal osteodystrophy in children on CAPD

High doses of calcitriol were used prospectively for 11 to 29 months to raise serum calcium levels in an effort to control renal osteodystrophy in 16 children undergoing CAPD. Serum Ca, P, iPTH and alkaline phosphatase were measured monthly; hand radiographs were obtained every six months, and a semiquantitative score of bone abnormalities was evaluated by two independent observers. During the study, serum Ca increased from 9.9 +/- 0.9 to 11.0 +/- 0.6 mg/dl (P less than 0.001); serum iPTH decreased by 113 +/- 131 microliter Eq/ml (P less than 0.005); serum P was unchanged; and serum alkaline phosphatase fell by 33 +/- 46% (P less than 0.02), 530 +/- 397 to 204 +/- 551 IU/liter. The radiographic score fell from 4.8 +/- 4.6 to 0.9 +/- 1.2 (P less than 0.005). The average and maximal doses of calcitriol were 0.61 +/- 0.37 and 0.95 +/- 0.56 microgram/day or 28 +/- 18 and 46 +/- 28 ng/kg body wt/day, respectively. Transient and asymptomatic hypercalcemia occurred in nine patients and two patients had reversible conjunctivitis in association with the hypercalcemia. Thus, "high dose" calcitriol prevented or controlled progression of hyperparathyroid bone disease in most pediatric CAPD patients. The failure to suppress PTH or reverse secondary hyperparathyroidism until the serum Ca rose to 10.5 to 11.0 mg/dl could reflect an increase in the "set point" for PTH suppression by serum calcium in many uremic children.