Bone disease in children and adolescents undergoing successful renal transplantation

Bone mineral density and bone histomorphometry in children on long-term dialysis

Bone mineral density (BMD) at the lumbar vertebrae (L(1)-L(4)) was assessed by dual-energy X-ray absorptiometry (DXA) in 20 children with chronic kidney disease (CKD) on dialysis, and its results were compared with bone biopsy and biochemical parameters. Biopsy specimens provided evidence of hyperparathyroid bone disease in eight cases (40%), and low bone turnover in 12 (60%). For BMD, expressed as Z-scores relative to normal, median Z-scores were -1.05 (range -2.36 to 1.06) for hyperparathyroid patients and -1.05 (range -4.40 to -0.03) for low bone turnover patients, with no statistical differences between groups (P = 0.512). In relation to BMD, of the whole sample, five (25%) had a Z-score under -2.0. When it was corrected for height, BMD was in the normal range. Additionally, there were no significant differences in single samples of serum calcium, alkaline phosphatase, phosphorus and intact parathyroid hormone (PTH) between groups with high or low bone turnover. Assessment of nutritional status, through height/age, showed that ten patients had Z-scores below -2.0 (median -2.12, range -7.13 to 0.73). In conclusion, renal osteodystrophy (ROD) seems to have a high prevalence among CKD pediatric patients, although only approximately a quarter of them developed changes in BMD. In children with CKD, measurements of bone mineral density may not be used for classification of various forms of ROD.

Bone alterations in children and young adults with renal transplant assessed by phalangeal quantitative ultrasound

BACKGROUND

Bone alterations in young renal transplant recipients were investigated in several studies with conflicting results. Quantitative ultrasound of the phalanges is a recently developed noninvasive procedure to assess skeletal status.

STUDY DESIGN

Cross-sectional study at a single transplant center with values compared with previously studied healthy controls.

SETTINGS & PARTICIPANTS

40 children and young adult recipients of renal grafts (15 females, 25 males; age, 20.0 +/- 8.4 years) studied 7.1 +/- 3.8 years after kidney transplantation.

PREDICTOR

Clinical, biochemical, and therapeutic features, including calcium, phosphate, and intact parathormone levels; and cumulative dosages of glucocorticoids and cyclosporine administered since transplantation.

OUTCOME & MEASUREMENT

Phalangeal quantitative ultrasound, including amplitude-dependent speed of sound (AD-SoS) and bone transmission time (BTT), mainly dependent on mineral density and cortical thickness, respectively. Age- and sex-matched healthy controls were used to provide age-related z scores; sex- and height-matched healthy subjects, to provide z scores related to statural age.

RESULTS

Mean z scores of AD-SoS and BTT were -0.05 +/- 1.59 and -0.54 +/- 1.17, respectively (P > 0.05 and P < 0.001, respectively). Multivariate analysis showed that AD-SoS z score was associated significantly with body mass index, intact parathormone level, cumulative glucocorticoids administered in the first posttransplantation year, and cyclosporine administered since transplantation (model r(2) = 0.79; P < 0.001); BTT z score was associated significantly with glucocorticoid dosage in the first posttransplantation year and age (model r(2) = 0.55; P < 0.001).

LIMITATIONS

Absence of other measures of bone structure and longitudinal measures and comparison to a noncurrent control group.

CONCLUSIONS

Children and young adults may have decreased cortical thickness with maintained overall mineral density after renal transplantation. The findings of phalangeal quantitative ultrasound parallel observations using other imaging techniques. Phalangeal quantitative ultrasound may be a useful method to assess bone alternations after renal transplantation.

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.

Evidence that calcineurin is required for the genesis of bone-resorbing osteoclasts

Here, we demonstrate that the Ca(2+)/calmodulin-sensitive phosphatase calcineurin is a necessary downstream mediator for osteoclast differentiation. Using quantitative PCR, we detected the calcineurin isoforms Aalpha, Abeta, Agamma (catalytic), and B1 (regulatory) in osteoclast precursor RAW-C3 cells. We found that, although the expression of these isoforms remained relatively unchanged during osteoclast differentiation, there was a profound increase in the expression of their primary substrate for calcineurin, nuclear factor of activated T cells (NFAT)c1. For gain-of-function studies, we incubated osteoclast precursors for 10 min with a calcineurin fusion protein (TAT-calcineurin Aalpha); this resulted in its receptorless influx into >90% of the precursor cells. A marked increase in the expression of the osteoclast differentiation markers tartrate-resistant acid phosphatase (TRAP) and integrin beta(3) followed. In addition, the expression of NFATc1, as well as the alternative substrate for calcineurin, IkappaBalpha, was significantly enhanced. Likewise, transfection with constitutively active NFAT resulted in an increased expression of both TRAP and integrin beta(3). In parallel loss-of-function studies, transfection with dominant-negative NFAT not only inhibited osteoclast formation but also reversed the induction of NFATc1, TRAP, and integrin beta(3) by TAT-calcineurin Aalpha. The expression of these markers was also inhibited by calcineurin Aalpha U1 small nuclear RNA, which significantly reduced calcineurin Aalpha mRNA and protein expression. Consistent with these observations, we observed a reduction in osteoclastogenesis in calcineurin Aalpha(-/-) cells and in osteoclast precursors treated with the calcineurin inhibitors cyclosporin A and FK506. Together, the gain- and loss-of-function experiments establish that calcineurin Aalpha is necessary for osteoclast formation from its precursor and that this occurs via an NFATc1-dependent mechanism.

Longitudinal growth in children following kidney transplantation: from conservative to pharmacological strategies

Impairment of longitudinal growth in children with chronic renal failure (CRF) is multifactorial. It is mainly due to disturbances in the growth hormone (GH)/insulin-like growth factor (IGF)/IGF-binding protein axis. Growth failure can be managed by optimizing nutrition and fluid/electrolyte homeostasis, and overcoming the growth-inhibiting effects of uremia by high-dose recombinant human (rh) GH treatment. A sufficient catch-up growth is one of the determining issues for the overall success of pediatric kidney transplantation (Tx). However, despite satisfactory renal function, spontaneous catch-up growth is often insufficient as glucocorticoid treatment is the main inhibiting factor for longitudinal growth after Tx. In addition, longitudinal growth may be jeopardized by low glomerular filtration rate (GFR) and African American or Hispanic background. Supraphysiological doses of GH and/or IGF-I in vitro and in vivo can partially overcome the growth-inhibiting effects of glucocorticoid treatment. GH-associated increase of leukocyte proliferation and cytotoxicity with stimulated interferon synthesis have been demonstrated. However, it is not clear whether such stimulatory effects on leukocyte function are a transitory or a constant risk factor after organ Tx. Clinical trials of GH in children after renal Tx have suggested a rather moderate or transient effect of rhGH on the immune system, and corticosteroids induce a hyporesponsiveness to the action of GH. As long as corticosteroids are believed to be essential after renal Tx, rhGH should be considered to optimize longitudinal growth in children.

Persistent secondary hyperparathyroidism after renal transplantation in children

Secondary hyperparathyroidism (HPTH) is a frequent complication of chronic kidney disease (CKD). Renal transplantation corrects the biochemical abnormalities that cause HPTH; however, HPTH persists in some patients. The factors that contribute to the persistence of HPTH after transplantation in children are poorly understood. We examined 57 children who underwent renal transplantation and determined whether baseline clinical and biochemical parameters could predict the persistence of HPTH at 1 year post-transplantation, using multivariate logistic regression. At the time of transplantation, serum parathyroid hormone (PTH) levels were >300 pg/ml in 60%, 150-300 pg/ml in 17%, and <150 pg/ml in 23% of recipients. HPTH (PTH >73 pg/ml) persisted in 78% of patients at 6 months and in 56% at 1 year after transplant. Older age at transplantation was the strongest predictor of HPTH at 1 year (OR=1.17, P<0.05). After adjustment for age, other baseline clinical or laboratory parameters were not predictive of HPTH at 1 year. The relationship between older age and persistent HPTH may be explained by longer duration of CKD. Given the potential morbidities associated with persistent HPTH, the role of interventions that would prevent or reverse persistent HPTH post-transplantation requires further investigation.

Bone disease after kidney transplantation

Advances in immunosuppressive therapy have allowed for enhanced allograft survival in kidney transplantation. With this increasing success of transplantation, however, has come a greater appreciation of subsequent complications, such as bone and mineral disease. In patients with chronic kidney disease who are awaiting transplantation, disorders in mineral metabolism and renal osteodystrophy are an essentially universal finding, and several different pathophysiologic mechanisms are believed to contribute to the development of these disorders.

Role of parathyroid hormone and therapy with active vitamin D sterols in renal osteodystrophy

Renal osteodystrophy (ROD) represents a spectrum of bone lesions ranging from a high-turnover to a low-turnover state. The expression of the histologic bone lesions is modulated by parathyroid hormone (PTH), vitamin D, calcium, phosphorus, and aluminum that act as major regulators of osteoblastic activity and bone formation rate. The availability of immunometric PTH assays has allowed reasonable prediction of the subtypes of bone lesions in patients with chronic kidney disease (CKD). PTH levels as measured by these assays, however, may not reflect the true bone turnover state during treatment with intermittent active vitamin D. Early diagnosis and appropriate treatment of renal bone disease are essential in preventing the debilitating consequences of ROD on the growing skeleton. Calcitriol and calcium-containing phosphate binders have been the mainstay of treatment for secondary hyperparathyroidism. Complications such as hypercalcemia, vascular calcifications, and the development of adynamic bone may arise from aggressive treatment. New vitamin D analogs and calcium-free phosphate binders are promising in terms of limiting these complications. The management of ROD should be tailored to maintain normal rates of bone formation and turnover with age-appropriate serum calcium and phosphorus levels and with serum PTH levels that correspond to normal rates of skeletal remodeling. These treatment goals would maintain bone health, maximize growth potential, and prevent the development of soft tissue and vascular calcifications.

Bone mineral content, corrected for height or bone area, measured by DXA is not reduced in children with chronic renal disease or in hypoparathyroidism

The combination of poor growth and parathyroid and mineral disorders complicates the diagnosis of renal bone disease in children with chronic renal insufficiency (CRI), and the role of dual X-ray absorptiometry (DXA) is unclear. We aimed to examine the role of DXA in assessing variation in size-adjusted bone mineral content (BMC) in children with CRI and compare it with a cohort with hypoparathyroidism (HPT) and pseudo-hypoparathyroidism (PHPIa). In 29 patients with CRI (21 male) with a median age of 11 years (10th, 90th centiles 4.4, 14.6) and 10 patients with HPT and PHPIa (three male), with a median age of 13.7 years (7, 16) lumbar spine (LS) and total body (TB) BMC were measured by DXA. Age-, gender- and height-matched data allowed calculation of percentage predicted bone area for age and gender (pBAr) and percentage predicted BMC for bone area and height. In the CRI group, the median glomerular filtration rate (GFR) was 27.4 ml/min per 1.73 m2 (7.1, 69.5), and the median duration of illness was 9.3 years (2.1, 12.1). Median height standard deviation score (Ht SDS) was -1.6 (-3.0, 0.3), and, as expected, median LS and TB pBAr were low at 82% (68, 974) and 76% (63, 92), respectively. LS and TB predicted BMC (pBMC) SDS (corrected for bone size) were generally high, with a median value of 0.4 (-0.9, 1.4) and 0.4 (-0.1,0.9), respectively. Analysis of the prepubertal subset of children (n=15) showed that median percentage predicted LS BMC for height was 104% (80, 116), whereas the median TB BMC for height was 96% (74, 108). Median Ht SDS of the HPT and PHPIa cohort was -0.3 (-2.9, 0.3) and median LS and TB pBAr were 90% (66, 100) and 91% (76, 98), respectively. Median LS and TB pBMC SDS were 0.6 (-0.4, 1.8) and 0.7 (0.3, 1.1), respectively. Median percentage predicted LS and TB BMC for height were 102% (82, 114) and 102% (92, 122). There was no relationship between pBMC SDS and duration of illness, GFR, vitamin D dose, serum intact parathyroid hormone (PTH), serum calcium/phosphate product or serum total alkaline phosphatase (ALP) in the CRI or the HPT cohort. However, one of the highest pBMC SDSs was recorded in a child with PHPIa before she started on any treatment. In children with CRI, BMC, when adjusted for co-existing growth retardation, is similar to that observed in children with hypoparathyroidism. The correct reading of BMC needs a correction for bone size.

Bone mineral density in pediatric and adolescent renal transplant patients: how to evaluate

Reduced bone mass is a common complication of renal transplantation in adults but only few data are present for pediatric transplant patients. Bone mineral status of pediatric renal transplant patients ages ranging from 7.5 to 17.6 years (mean age 14.9 +/- 2.3) who were at least 6 months postrenal transplantation was examined. Bone mineral density (BMD) of lumbar vertebrea and femoral neck was determined by dual energy X-ray absorptiometry (DEXA) and z-scores according to age, puberty, height and bone age were compared to sex and ethnic specific reference data. z-scores were calculated for both areal and volumetric bone density. BMD L1-4 z-scores were more than 2 SD below the mean according to chronological age in 12 patients (63%), pubertal status in six patients (31.5%), bone age in five patients (26.3%) and height in five patients (26.3%). The BMD femoral neck z-scores were more than 2 SD below the mean according to age in 10 patients (55.5%), puberty in five patients (27.7%), bone age in three (16.6%) patients and height in five (26.3%) patients. Correction of the vertebrae and femoral neck for bone size yielded osteoporotic values for seven patients (36.8%) for lumbar BMD and for four patients (22%) for femoral neck BMD. The use of aBMD in growth-retarded children has some restrictions in determining z-scores. Deficits in spinal bone density still persisted after correcting for height, puberty, bone age and volume. In renal transplant patients who have short stature it is reasonable to give values corrected for height, puberty, bone age and bone size and interpret each of these values for each patient.

Sevelamer controls parathyroid hormone-induced bone disease as efficiently as calcium carbonate without increasing serum calcium levels during therapy with active vitamin D sterols

Little is known about the impact of various phosphate binders on the skeletal lesions of secondary hyperparathyroidism (2 degrees HPT). The effects of calcium carbonate (CaCO3) and sevelamer were compared in pediatric peritoneal dialysis patients with bone biopsy-proven 2 degrees HPT. Twenty-nine patients were randomly assigned to CaCO3 (n = 14) or sevelamer (n = 15), concomitant with either intermittent doses of oral calcitriol or doxercalciferol for 8 mo, when bone biopsies were repeated. Serum phosphorus, calcium, parathyroid hormone (PTH), and alkaline phosphatase were measured monthly. The skeletal lesions of 2 degrees HPT improved with both binders, and bone formation rates reached the normal range in approximately 75% of the patients. Overall, serum phosphorus levels were 5.5 +/- 0.1 and 5.6 +/- 0.3 mg/dl (NS) with CaCO3 and sevelamer, respectively. Serum calcium levels and the Ca x P ion product increased with CaCO3; in contrast, values remained unchanged with sevelamer (9.6 +/- 01 versus 8.9 +/- 0.2 mg/dl; P < 0.001, respectively). Hypercalcemic episodes (>10.2 mg/dl) occurred more frequently with CaCO3 (P < 0.01). Baseline PTH levels were 980 +/- 112 and 975 +/- 174 pg/ml (NS); these values decreased to 369 +/- 92 (P < 0.01) and 562 +/- 164 pg/ml (P < 0.01) in the CaCO3 and the sevelamer groups, respectively (NS between groups). Serum alkaline phosphatase levels also diminished in both groups (P < 0.01). Thus, treatment with either CaCO3 or sevelamer resulted in equivalent control of the biochemical and skeletal lesions of 2 degrees HPT. Sevelamer, however, maintained serum calcium concentrations closer to the lower end of the normal physiologic range, thereby increasing the safety of treatment with active vitamin D sterols.

Assessment of bone mass following renal transplantation in children

Throughout childhood and adolescence, skeletal growth results in site-specific increases in trabecular and cortical dimensions and density. Childhood osteoporosis can be defined as a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture. Pediatric renal transplant recipients have multiple risk factors for impaired bone density and bone strength, including pre-existing renal osteodystrophy, delayed growth and development, malnutrition, decreased weight-bearing activity, inflammation, and immunosuppressive therapies. Dual energy X-ray absorptiometry (DXA) is the most-common method for the assessment of skeletal status in children and adults. However, DXA has many important limitations that are unique to the assessment of bone health in children. Furthermore, DXA is limited in its ability to distinguish between the distinct, and sometimes opposing, effects of renal disease on cortical and trabecular bone. This review summarizes these limitations and the difficulties in assessing and interpreting bone measures in pediatric transplantation are highlighted in a review of select studies. Alternative strategies are presented for clinical and research applications.

Analysis of the functional muscle-bone unit of the forearm in pediatric renal transplant recipients

BACKGROUND

Renal transplantation in children and adolescents is associated with various skeletal complications. The incidence of spontaneous fractures appears to be increased, but the reasons for this are not entirely clear. Our objective was therefore to evaluate macroscopic bone architecture, mass, and strength by peripheral quantitative computed tomography (pQCT), a method that is not influenced by size-related artifacts. In addition, we investigated the muscle-bone relationship in these patients because under physiologic conditions bone strength continually adapts to increasing mechanical loads, that is, muscle force.

METHODS

In 55 patients (41 males) aged 15.8 +/- 4.1 years, we evaluated in a cross-sectional study 4.9 +/- 3.6 years after renal grafting bone mass, density, geometry, and strength of the radius, as well as forearm muscle size and strength, using pQCT at the proximal and distal radius, radiography of the second metacarpal shaft and hand dynamometry. Data were compared to a large cohort (N= 350) of healthy children.

RESULTS

Muscle mass and force were adequate for body size in pediatric renal transplant recipients. However, the radial bone was characterized by an inadequately thin cortex in relation to muscular force, as shown by a reduced height-adjusted cortical thickness both at the proximal (-0.83 +/- 1.12 SDS) and distal radius (-0.52 +/- 1.69 SDS), the metacarpal shaft (-0.54 +/- 1.35 SDS), and by a reduced relative cortical area (-0.90 +/- 1.13 SDS), while the mineralization of trabecular bone was unaltered. As a consequence of cortical thinning, the Strength-Strain Index that reflects the combined strength of trabecular and cortical bone was reduced in these patients.

CONCLUSION

While bone mineral density of the forearm is not decreased in pediatric renal transplant recipients, bone strength in relation to muscular force is reduced. This alteration may contribute to the increased propensity for fractures in these patients.

Osteoporosis in chronically ill children

Gains in bone mass are very rapid during adolescence and peak bone mass, the most important determinant of osteoporosis, is attained by early adulthood. Glucocorticoids, widely used in children with chronic illness, are known to impact bone mass and quality. In addition, disease and treatment-related factors, nutrient and hormone deficiencies and decreased physical activity may all negatively affect bone mass accrual. Although decreased bone density is increasingly recognized in chronically ill children, current knowledge of the epidemiology, diagnosis and optimal treatment of pediatric secondary osteoporosis is limited. In addition to bone densitometry, biochemical and radiographic tests should be used in the diagnosis of osteoporosis. Bone histomorphometry may be needed in selected situations. At risk children should be advised to ensure sufficient calcium and vitamin D intake and weight bearing physical activity. Growth and pubertal development require careful assessment because of their close correlation with bone formation. Given limited experience with bisphosphonates, it seems prudent to target antiresorptive therapy to those children who have developed symptomatic disease. Ideally this should be done in controlled settings. Early identification and adequate intervention, in selected cases with bisphosphonates, is needed in order to prevent deleterious skeletal complications of osteoporosis in chronically ill children.

A prospective randomized study for the treatment of bone loss with vitamin d during kidney transplantation in children and adolescents

The effect of treatment with alfacalcidol on post-transplantation bone loss in children and adolescents was investigated. Of the 63 young patients who received renal transplant and were subjected to dual-energy x-ray absorptiometry (DEXA), 30 patients had low-bone mineral density (BMD) (z-score < or = -1) and were enrolled into the study. Their mean age at the time of transplantation was 14.5 +/- 4.0 years and the mean duration after transplantation was 48 +/- 34 months. Patients with low BMD were randomized into two equal homogeneous groups: group 1 (control) received placebo and group 2 received daily alfacalcidol 0.25 microg by mouth. Parameters of bone metabolism (intact parathyroid hormone, serum osteocalcin and urinary deoxypyridinoline) and BMD were assessed before and after the study period. After 12 months of treatment BMD at the lumber spine decreased from -2.2 to -2.5 in group 1 while it increased from -2.1 to -0.6 in group 2 (p < 0.001). Serum intact parathyroid hormone level decreased significantly in group 2 (p = 0.042). Apart from transient hypercalcemia in 1 patient in group 2, no other significant adverse effects were noted. This study suggested the value of alfacalcidol in the treatment of bone loss in young renal transplant recipients.

Osseous complications of pediatric transplantation

Adult stature and peak bone mass are achieved through childhood growth and development. Multiple factors impair this process in children undergoing solid organ transplantation, including chronic illness, pretransplant osteodystrophy, use of medications with negative impact on bone, and post-transplant renal dysfunction. While growth delay and short stature remain common, the most severe forms of transplant-related bone disease, fracture and avascular necrosis, appear to have become less common in the pediatric age group. Osteopenia is very prevalent in adult transplant recipients and probably also in pediatrics, but its occurrence and sequelae are difficult to study in these groups due to methodological shortfalls of planar densitometry related to short stature and altered patterns of growth and development. Although the effect on lifetime peak bone mass is not clear, data from adult populations suggest an elevated long-term risk of bone disease in children receiving transplants. Optimal management of pretransplantation osteodystrophy, attention to post-transplant renal insufficiency among both renal and non-renal transplant patients, reduction of steroid dose in select patients, and supplementation with calcium plus vitamin D during expected periods of maximal bone loss may improve bone health. Careful research is required to determine the role of bisphosphonate therapy in pediatric transplantation.

Interleukin-6, transforming growth factor-beta 1, and bone markers after kidney transplantation

The aim of this study was to investigate the relationship between interleukin 6 (IL-6), transforming growth factor (TGF)-beta 1, IL-6 soluble receptors, and biochemical parameters of bone turnover after kidney transplantation. Of 64 patients enrolled in the study, 19 received the kidney transplant 2 to 12 months before the study, and 45 within the previous 15 to 175 months. We measured IL-6, TGF-beta 1, intact parathyroid hormone (PTH) bone alkaline phosphatase (BALP), osteocalcin (OC), and procollagen type I propeptide (P1CP) concentrations in the serum, and deoxypyridinoline crosslinks (DPD) in the urine of the patients. In 16 patients in the first posttransplantation year, the concentrations of IL-6 (P = 0.02), TGF-beta 1 (P = 0.01), BALP (P = 0.0002), OC (P = 0.001), and DPD (P = 0.01) were significantly higher than in patients with longer posttranslation period. Statistically significant negative correlation was found between post-transplantation time and IL-6 (P = 0.04), BALP (P = 0.003), OC (P = 0.0009), P1CP (P = 0.03), and DPD (P = 0.01) concentrations. Repeated measurements of the investigated parameters in the first post-transplantation year showed a significant decrease only in TGF-beta I level. In all patients, IL-6 correlated positively with PTH (P = 0.0009) and DPD (P = 0.03), and IL-6 soluble receptor (IL-6 sR) with DPD (P = 0.03). A decrease in IL-6 and TGF-beta 1 concentrations that paralleled the decrease in bone turnover markers in the posttransplantation period indicated that IL-6 and TGF-beta 1 were probably involved in the bone turnover after kidney transplantation.

Conjugated linoleic acid reduces parathyroid hormone in health and in polycystic kidney disease in rats

BACKGROUND

Feeding conjugated linoleic acid (CLA) is reported to reduce prostaglandin E(2) synthesis, which is required for parathyroid hormone (PTH) release.

OBJECTIVE

This study was undertaken to determine whether CLA would suppress hyperparathyroidism and the resulting high-turnover bone disease in a rat model of polycystic kidney disease (PKD).

DESIGN

Outcome measurements were conducted after 8 wk of feeding diets supplemented with and without CLA (1% of dietary fat) to Han:SPRD-cy male rats (n = 52). PTH, bone formation, and resorption were assessed in addition to femur bone mass with use of dual-energy X-ray absorptiometry.

RESULTS

CLA feeding resulted in attenuation of PTH concentrations in both PKD-affected and nonaffected rats (by 60%) but did not significantly alter bone formation and resorption.

CONCLUSION

Reduction in PTH may open possibilities for CLA as an adjunctive therapy in secondary hyperparathyroidism.

Bone disease after kidney transplantation

Kidney transplantation is the optimal form of renal replacement therapy for many with end-stage kidney disease. However, kidney transplantation comes with a unique set of medical complications, important among them is bone disease. Posttransplant bone disorders are manifestations of pathologic processes occurring posttransplant that are superimposed on preexisting disorders of bone and mineral metabolism secondary to kidney failure and/or diabetes mellitus. As a consequence of early rapid bone loss, which is seen commonly within the first 3 to 6 months of transplant, the fracture risk posttransplant increases and has been reported as high as 5% to 44%. Posttransplant fractures occur more commonly at peripheral than central sites. Patients with a history of diabetes mellitus are at particular risk for fracture. Parathyroid hormone (PTH) and osteocalcin levels generally decrease after transplantation. Alkaline phosphatase and urinary collagen cross-links are unpredictable. Bone histology varies. No single biomarker unequivocally distinguishes between the various bone disorders found on biopsy examination. Immunosuppression is a major cause of posttransplant bone disorders. Glucocorticoids lead to decreased bone formation whereas the calcineurin inhibitors appear to cause increased bone turnover. Evaluating and managing posttransplant bone disease is an integral part of posttransplant medical care.

Long-term outcomes in pediatric renal transplant recipients who survive into adulthood

BACKGROUND

Long-term results in renal transplant recipients who underwent transplantation as children are often buried within the outcomes of adult centers, leaving a void in our knowledge regarding this unique cohort. The authors aim to describe the long-term outcomes of children who experienced renal failure and subsequently underwent transplantation during childhood and who have now reached adulthood, with an emphasis on social and economic rehabilitation.

METHODS

Two hundred seventeen children were identified who underwent transplantation between 1967 and 1999. Of those 217174 who were born before October 1982 and who would therefore have reached adulthood were selected for study. A questionnaire and consent form were sent to the surviving 132 patients of this subpopulation.

RESULTS

Fifty-seven adult survivors answered the questionnaire. No significant differences were found comparing the respondents to the nonrespondents. Nearly half of all respondents were severely short and 27% were obese. Questionnaire respondents had high rates of hypertension, bone and joint symptoms, fractures, hypercholesterolemia, and cataracts. Despite significant remaining health issues, 82% of respondents were employed, 95% reported their health as "fair" or "good," 61% reported "no" or "minor" physical limitations, and 82% described themselves as "just as" or "more content than others." Nearly 50% of the respondents were married, and the overwhelming majority reported satisfaction in their sexual lives.

CONCLUSIONS

Despite a high retransplantation rate and the presence of significant morbidity, renal transplantation in children can lead to attainment of a productive and satisfying life, with a high degree of rehabilitation in adulthood.

Decreased bone mineral density in the pediatric renal transplant population

All renal transplant recipients at our centre have had bone mineral density assessment (BMD) by DEXA scans of their lumbar spine while on the transplant waitlist and at 6-month intervals post-transplant over the past 7 yr. Risk factors for osteopenia and osteoporosis including donor source, dialysis status prior to transplantation, prior renal disease, and biopsy confirmed rejection events and their relationship to BMD of the lumbar spine were assessed. Thirty-nine children transplanted over the past 7 yr were included in this study. In total, 127 BMD longitudinal assessments were performed. From 1990 to 1997, ATG/ALG was used as antibody induction therapy. From 1997 to 2002, Basiliximab was utilized. Cyclosporin A (CyA) was the primary immunosuppressant for most children with tacrolimus as primary (n = 2) and switch for CyA failure or toxicity (n = 16). Prednisone was administered at a dose of 1 mg/kg/day for the first week and tapered to 10 mg/m2/alternate day by 1 month post-transplant. Azathioprine 1.5 mg/kg/day was continued for 1 yr and discontinued in children who were rejection free. All rejections were biopsy confirmed and treated with a prednisone pulse. Using a repeated measures regression analysis, we have found that L1-L4 BMD z score is affected by height and transplant number. It is also related to time relative to transplant in a quadratic fashion. There was an inverse relationship between advancing patient age and L1-L4 BMD z score. L1-L4 BMD z score was not related to weight, pre-existing renal disease, gender, donor source, type of renal replacement therapy prior to transplantation, or rejection events.

Assessment of bone health in children and adolescents with cancer: promises and pitfalls of current techniques

During childhood and adolescence, skeletal development is characterized by gender-, face-, and maturation-specific increases in cortical dimensions and trabecular density. Children with cancer have multiple risk factors for impuired bone mineralization, including delayed growth and maturation, sex hormone deficiencies, decreasal physical activity and biomechanical loading of the skeleton, glucocorticoid and other immunosuppressive therapies, growth hormone deficiency, and malnutrition. This review outlines the expected gains in bone dimensions, mineral content and strength during childhood and adolescence. Varied threats to bone health in the child with cancer are summarized, with special attention to potential effects on bone formation and resorption in the growing skeleton. The strengths and limitations of dual energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT) techniques in the assessment of the different disease-related effects on bone strength are discussed, and alternative analytic approaches explored.

Bone mineral density in pediatric transplant recipients

BACKGROUND

Reduced bone mass and fragility fractures are known complications after transplantation in adults. Far less is known about the skeletal effects of transplantation in children and adolescents.

METHODS

This cross-sectional study examined the skeletal status of children (ages 9-18 years) who were at least 1 year post-cardiac (n=13), post-renal (n=8), or post-bone marrow (BMT; n=15) transplantation. Bone mass at total hip, femoral neck, spine (L2-4), and whole body (WB) was determined by dual energy x-ray absorptiometry and compared with age, sex, and ethnic-specific reference data. Standard deviations (z-scores) were calculated for both areal bone mineral density (BMD) and estimated volumetric bone density (bone mineral apparent density [BMAD]).

RESULTS

Cardiac transplant patients had significantly lower BMD z-scores compared with the reference population at all skeletal sites. BMT recipients had significantly reduced BMD z-scores at total hip, spine, and WB. Kidney transplant patients had a significantly reduced WB BMD z-score only. Spine BMAD z-scores remained significantly reduced in cardiac and BMT subjects. Three of 36 patients had radiographic evidence of spinal fracture after transplantation. No correlation between steroid dosage and any measure of bone mass was observed.

CONCLUSIONS

Cardiac and BMT recipients had reduced BMD at multiple skeletal sites, and renal transplant recipients had reduced WB BMD for age. Deficits in spine bone density persisted after correcting for small bone size using BMAD. Low bone density and the occurrence of vertebral fractures indicate that cardiac, renal, and bone marrow transplantation in children is associated with reduced bone health.

Renal bone disease: a new conceptual framework for the interpretation of bone histomorphometry

My purpose in this article is to restore the histologic appraisal of renal bone disease to the mainstream of bone and mineral metabolism from which it has been separated for many years. Historically, both the two major components were found in varying degrees in most patients, although one or other of them often predominated. For more than 15 years bone biopsy has been used almost exclusively to classify individual patients into hyperparathyroid, osteomalacic, mixed and adynamic categories according to rigid non-overlapping criteria, and remarkably few histologic data have been reported. All metabolic bone diseases result from disordered bone remodeling, the physiologic mechanism for replacing bone that has become too old to carry out its mechanical or metabolic functions. Bone remodeling is not directly concerned with the regulation of plasma calcium, which reflects the level of equilibration at quiescent bone surfaces between systemic and bone extracellular fluid set by parathyroid hormone. The separation of remodeling from homeostasis explains the concurrence of increased turnover and decreased plasma calcium in chronic renal failure; it is the homeostatic system, rather than the remodeling system, which is resistant to parathyroid hormone. The effect of mild hyperparathyroidism is a nonspecific increase in bone turnover, of which the best index is the bone formation rate measured by double tetracycline labeling expressed per unit of bone surface. Increased turnover is always accompanied by increased reversible mineral deficit. In prolonged hyperparathyroidism there is also accelerated irreversible bone loss manifested mainly as thinning of cortical bone, detectable in chronic renal failure before any symptoms, due to increased resorption depth on the endocortical surface. In severe hyperparathyroidism resorbed bone is replaced, not by a lesser quantity of normal bone, but by a mixture of vascular fibrous tissue and woven bone, referred to as osteitis fibrosa. In osteomalacia there is increased accumulation of osteoid, due not to increased turnover, but to prolongation of mineralization lag time, which in conjunction with increased thickness, surface and volume of osteoid is diagnostic. Converting histomorphometric data into category assignment discards most of the useful information, which can be retained by two-dimensional representation of severity. For the hyperparathyroid dimension, bone formation rate measured by double tetracycline labeling expressed per unit of bone surface is the most useful although not ideal. For the osteomalacic dimension a mineralization index was constructed that is unaffected by age or race. In patients with osteitis fibrosa, bone formation rate per unit of bone surface and mineralization index were inversely correlated. For the third dimension a structure/formation index was constructed which increases with age in healthy women and shows weak inverse correlation with bone formation rate. The structure/formation index is lower than normal in patients with osteitis fibrosa, and should be useful in the study of osteopenia in chronic renal failure. Bone formation rate is low in osteomalacia, but some patients have subnormal rates through quite a different mechanism. The frequency of this finding has been overestimated for several reasons: failure to exclude atypical osteomalacia (increased surface and volume but not thickness of osteoid), use of inappropriate reference values, and failure to measure the bone formation rate on endocortical and intracortical surfaces. In healthy women bone formation rate can be zero on the cancellous surface alone. Low bone formation rate is sometimes due to diabetes but most often is the expected response to subnormal parathyroid hormone secretion accompanying an excess of calcium, a situation recognized only recently because of improvement in parathyroid hormone assay methodology. Low cancellous bone formation rate should not increase fracture risk because turnover is much lower in the peripheral than in the central skeleton, and all reports of increased fracture risk are flawed or open to different interpretation. Low bone formation rate is associated with reduced skeletal buffering of calcium and increased soft tissue calcification. This is not a new disease needing its own treatment, however, but represents the final stage of skeletal adaptation to a surfeit of calcium. The concept of adynamic bone disease has been harmful by directing attention away from the most important consequence of over-treatment of hyperparathyroidism.

Bone disease in long-term adult kidney transplant patients with normal renal function

BACKGROUND

In successful renal transplantation, the degree of renal function recovery is usually incomplete and information is scarce about the abnormalities of mineral metabolism in long-term adult renal recipients with normal renal function. This study was designed to investigate bone mineral metabolism in patients with a long-term normal functioning kidney.

METHODS

Twenty-nine adult asymptomatic renal transplant (RT) recipients with stable graft function for more than 10 years and serum creatinine <2 mg/dL were studied. They were classified into two groups according to glomerular filtration rate: Group A (N = 12; nine men, three women)>70 mL/min (x: 126 +/- 55 mL/min) and Group B (N = 17; nine men, eight women) <70 mL/min (x: 56 +/- 11 mL/min). Circulating biochemical markers of bone remodelling, bone histomorphometry, and densitometry (lumbar spine and hip) were obtained to investigate bone disease in these patients.

RESULTS

Serum PTH was slightly elevated in 10 patients (83%) in group A. Serum PTH levels were positively related to serum calcium, osteocalcin, BAP, telopeptide, OH-proline, and creatinine. There was no histologic data to support overactivity on bone in this group of patients, with only one showing high bone turnover. Mineralization was prolonged in 34% of patients. Twenty-two patients (75%) exhibited normal bone turnover. In the group with GFR>70 mL/min the prevalence of mineralization defect in the presence of normal serum levels of calcitriol suggested vitamin D resistance. Lumbar and femoral neck osteoporosis was present in 25% and 33% of patients in group A, and 23% and 53% in group B, respectively. T-score at lumbar spine was negatively correlated with months since transplantation. Patients under treatment with cyclosporine (CsA) showed increased concentrations of osteocalcin and D-pyr and higher lumbar bone mineral density (BMD), but bone histomorphometry was not influenced by CsA.

CONCLUSION

Patients with long-term renal transplantation with normal renal function frequently present with slight increases in PTH, but without an effect on bone histology. CsA did not induce changes in bone histology and delayed mineralization was frequently observed.

Similar predictive value of bone turnover using first- and second-generation immunometric PTH assays in pediatric patients treated with peritoneal dialysis

BACKGROUND

Accurate measurements of the concentration of parathyroid hormone (PTH) in serum or plasma are essential for the proper assessment of renal osteodystrophy. The first-generation immunometric PTH assay (1st PTH-IMA) not only detects the intact hormone, but also additional PTH fragments truncated at the amino N-terminally truncated PTH-derived fragments [ntPTH(1-84)]. A second-generation immunometric PTH assay (2nd PTH-IMA) recognizes only PTH(1-84) and possibly PTH fragments that are truncated at the carboxyl-terminus but not PTH(7-84). Whether estimates of the ratio between PTH(1-84) and ntPTH(1-84) fragments are a better predictor of bone turnover remains controversial.

METHODS

Thirty-three patients aged 12.8 +/- 4.4 years treated with continuous cycling peritoneal dialysis (CCPD) for 13 +/- 9 months underwent iliac crest bone biopsy. PTH levels were measured by two newly developed first-generation and second-generation PTH-IMA. The ntPTH(1-84) fragments were calculated by subtracting PTH values determined using the 2nd PTH-IMA from values obtained using 1st PTH-IMA that detects both PTH(1-84) and relatively large ntPTH(1-84).

RESULTS

Determinations of PTH levels by both assays were highly correlated (r = 0.89, P < 0.001). The relationships between first-generation and second-generation PTH-IMA and bone formation were similar (r = 0.67, P < 0.0001 and r = 0.64, P < 0.0001, respectively). When patients were grouped according to the presence or absence of secondary hyperparathyroidism, the ratio PTH(1-84) to ntPTH(1-84) did not differ between groups.

CONCLUSION

PTH concentrations determined by either the first- or the second-generation PTH-IMA were found to be better predictors of bone formation than the PTH(1-84) to ntPTH(1-84) fragments ratio.

Osteopenia and fractures in cystinotic children post renal transplantation

Many of the end-organ effects of cystinosis are known to be risk factors for osteopenia; these include deposition of cystine crystals in bone, hypothyroidism, diabetes mellitus, primary hypogonadism, urinary phosphate wasting, and chronic renal failure. While transplantation may correct the latter, it exposes the child to other risk factors for diminished bone mass, notably the use of high-dose glucocorticoids. Our objective was to determine if these multiple risk factors translate into an increased occurrence of osteopenia, as measured by dual-energy X-ray absorptiometry (DEXA), and/or fractures in this population. We examined the charts, X-rays, and bone mineral density (BMD) of all cystinotic patients post renal transplant for whom this information was available. Lumbar spine BMD was measured by DEXA scan (Hologic 4500). Z-scores were corrected for growth parameters using previously published reference data. Fracture history and pertinent serum markers of bone metabolism were also analyzed. Of the 63 renal transplants performed at our institution, 11 children were transplanted due to cystinosis. Nine of these patients, 5 male and 4 female, had had BMD evaluations, with an average age of 14.3 years (range 5-17 years) at the time of initial BMD post transplant. The mean interval between transplant and BMD evaluation was 39 months (range 3-90 months). Surprisingly, 7 of 9 patients had normal uncorrected BMD values (z-scores -1.92 to +0.02) and 7 of 9 patients had normal corrected values (z-scores -1.20 to +1.93). Three patients suffered from a total of eight fractures. Of the 3 fracture patients, 2 had normal BMD. All patients maintained good graft function and had normal calcium/phosphate mineral status. Of note, 3 of 5 male patients had evidence of primary testicular failure at earlier ages than often described, and this may be an unrecognized risk factor for bone disease in this population. Despite the numerous risk factors for developing osteopenia, these results suggest that the majority of cystinotic patients post renal transplant do not experience reduced bone mineral content as measured by DEXA. However, the significant fracture history among these patients demonstrates that DEXA cannot be used to assess fracture risk in patients with nephropathic cystinosis.

Zoledronic acid to prevent bone loss in the first 6 months after renal transplantation

BACKGROUND

Bisphosphonates can prevent bone mineral density loss after renal transplantation, but their effect on trabecular mineralization and bone morphology, two key factors of bone stability, remains unknown.

METHODS

In a 6-month, randomized, placebo-controlled study, 20 kidney transplant recipients received either 4 mg zoledronic acid or placebo twice within 3 months after engraftment. At transplantation and after 6 months, mean trabecular calcium concentration and trabecular morphometry were measured in bone biopsies. Bone mineral density (BMD) of the femoral neck and the lumbar spine were evaluated by dual-energy x-ray absorptiometry, and serum biochemical markers of bone metabolism were determined monthly.

RESULTS

Trabecular calcium content increased significantly in the zoledronic acid group, but remained unchanged in the placebo group. BMD at femoral neck showed no change in the zoledronic acid group, but decreased in the placebo group. BMD of the lumbar spine was increased in the zoledronic acid group without change in the placebo group. High-turnover bone disease resolved similarly in both groups, as evidenced by a significant decrease of eroded bone surface, osteoclast and osteoblast surface. Serologic markers of bone formation and resorption were significantly lower in zoledronic acid-treated patients throughout the study. Kidney transplant function was stable after zoledronic acid therapy.

CONCLUSIONS

Our results show that administration of zoledronic acid improves the calcium content of cancellous bone after kidney transplantation. The beneficial effect of bisphosphonate therapy is further evidenced by an increase of lumbar spine BMD, and stabilization of femur BMD.

Changes in bone mineral density, insulin-like growth factor-1 and insulin-like growth factor binding protein-3 in kidney transplant recipients. A longitudinal study

BACKGROUND

Osteopenia is a major complication of renal transplantation (RTx). This cross-sectional and longitudinal study was planned to better define long-term bone status and relationship to IGF system components.

METHODS

Serial measurements of bone mineral density (BMD) and serum markers were performed in 30 patients prior to RTx and at 6 and 12 months following RTx. Serum concentrations of insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), vitamin D, and intact parathyroid hormone (iPTH) were measured.

RESULTS

Serum creatinine, phosphate, alkaline phosphatase and osteocalcine levels decreased, serum calcium levels increased and serum iPTH levels did not change significantly after transplantation. The mean BMD of the vertebrae was 0.97 +/- 0.22 g/cm(2) at the time of RTx, 0.87 +/- 0.21 g/cm(2) 6 months post-RTx (p < 0.05), and 0.81 +/- 0.21 g/cm(2) 12 months post-RTx (p < 0.05). Femur BMD also declined from 0.79 +/- 0.16 to 0.72 +/- 14 g/cm(2) at 12 months (p < 0.05). There was a significant increase in the IGF-1 and a significant reduction in the IGFBP-3 concentrations at 6 months post-RTx (p < 0.05). Significant correlations between serum IGF-1 concentrations and vitamin D concentrations were noted only at 6 months. There was no significant correlation between the BMD and serum IGF system.

CONCLUSIONS

These results demonstrate a significant loss of BMD after RTx. The circulating levels of IGF-1 and IGFBP-3 stimulated by the reduction in BMD and IGF-1 secretion are increased in order to restore bone formation.

Current concepts in pediatric bone disease

It is widely believed that osteoporosis prevention may be best accomplished during childhood and adolescence, when bones are growing rapidly and are most sensitive to environmental influences, such as diet and physical activity. For children with chronic diseases, a variety of factors may influence normal bone mineralization, including altered growth, delayed maturation, inflammation, malabsorption, reduced physical activity, glucocorticoid exposure, and poor dietary intake. In healthy children, maintaining adequate levels of calcium intake, serum vitamin D, and weightbearing physical activity may be sufficient to prevent osteoporosis later in life. Far less is known about effective prevention and treatment of poor bone mineralization in children with chronic illness, such as CF or CD. Osteoporosis prevention and intervention measures during childhood are limited by the paucity of reference data on bone mineralization. Although it is widely recognized that puberty, skeletal maturation, and body size influence BMC and bone density, no reference data for bone mineralization are scaled to these important measures. In children with chronic disease with delayed growth and maturation, the creation of such reference data is of paramount importance. In addition, the dynamic changes that occur during growth and maturation in the structural characteristics of trabecular and cortical bone and the development of the bone-muscle unit may influence current and future fracture risk. Further research is needed to characterize these changes and their use in the assessment of bone health and fracture risk in children. Only then can the impact of treatment strategies be appreciated fully.

Assessment of bone mineralization following renal transplantation in children: limitations of DXA and the confounding effects of delayed growth and development

Pediatric renal transplantation recipients have numerous risk factors for decreased bone mass, including the underlying renal disease, nutritional deficits, decreased physical activity, inflammation and exposure to steroid therapy. The assessment of bone mineralization in children following renal transplantation is fraught with difficulty. Dual energy x-ray absorptiometry (DXA) is the most commonly employed tool to assess bone mineralization. However, DXA has important limitations in children and in individuals with renal disease. This brief review will examine the expected gains in bone size and bone mass during growth and the mechanisms by which renal failure and steroid therapy interrupt these process. In addition, the limitations of DXA for detecting impaired bone mineralization in children with renal disease are reviewed and alternative approaches explored.

The prevalence of osteopenia in pediatric renal allograft recipients varies with the method of analysis

BACKGROUND

Pediatric renal allograft recipients often suffer from osteopenia and the potential for increased fractures. Although modern densitometers are widely available, their use in children is complicated by lack of optimal interpretive criteria.

METHODS

We reviewed dual energy X-ray absorptiometry (DEXA) studies in 33 patients with functional renal allografts 4.4 +/- 3.6 years after transplantation. We interpreted our data using three previously described methods of assigning bone mineral density (BMD) Z scores.

RESULTS

BMD was directly related to age, height, weight, body surface area, and pubertal status (p < 0.001). Using gender-mixed reference data matched by chronological age, the mean BMD Z score was -0.9 +/- 1.3 vs. 0.4 +/- 1.4 when matched by height-age (p < 0.001). Height-age adjustment particularly increased the BMD Z score of pubertal adolescents. In a subset of 22 patients, gender-matched reference data led to different results from the gender-mixed reference population (mean BMD Z score 0.0 +/- 1.7 vs. -0.8 +/- 1.4, p < 0.001).

CONCLUSIONS

The perceived prevalence of osteopenia among pediatric kidney transplant recipients differs using analysis based on chronological age, height-age, or gender-matched reference data. Further studies are necessary to determine the clinical significance of measured bone density in this population.

Preservation of bone mass in pediatric dialysis and transplant patients

Renal osteodystrophy continues to be a major challenge to the physician treating the child with end-stage renal disease (ESRD). The gold standard for the assessment of bone status is bone histomorphometry, which divides bone pathology into 3 main types; high-turnover, low-turnover, and mixed disease. The high-turnover disease, related to hyperparathyroidism, has been the one most extensively investigated; however, optimal therapy, especially in the growing child, is yet unclear. Overzealous treatment might result in adynamic bone disease (an extreme example of low-turnover disease), and further interference with statural growth. Pre-existent bone disease after kidney transplantation seems to worsen immediately, probably because of the high dose of corticosteroids used. In children who attain normal kidney function in the allograft, bone status seems to improve over time. Little is known about bone in transplanted patients with reduced glomerular filtration rate (GFR). The correlation between bone histology and its main surrogates, bone remodeling markers and bone mineral density, is yet unclear, but it might serve to follow the progress of an individual patient. New therapeutic modalities aimed at suppressing hyperparathyroidism, and consequently bone resorption, as well as agents directly attenuating bone resorption, should be further investigated for their effect on bone in patients with ESRD or after transplantation. Similarly, agents stimulating bone formation, particularly growth hormone, require further attention for their potential to improve bone status. Bone health and the child's somatic growth at ESRD or after kidney transplantation are closely related, and therapy should be aimed at achieving optimal results for both.

Osteopenia in adolescent idiopathic scoliosis: a histomorphometric study

STUDY DESIGN

Bone biopsies from iliac crest and spinous process of adolescent idiopathic scoliosis patients were obtained intraoperatively for histology and histomorphometric analysis.

OBJECTIVES

To study the histologic features of cancellous bone and to correlate the histomorphometric variables with preoperative bone mineral density in patients with adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Low bone mineral density has been reported in adolescent idiopathic scoliosis. However, there is limited information about the histopathologic changes.

METHODS

Undecalcified and decalcified bone specimens from iliac crest and spinous process of adolescent idiopathic scoliosis patients obtained intraoperatively were stained with Goldner and hematoxylin & eosin stain, respectively. Results were correlated with bone mineral density of the lumbar spine (L2-L4) and proximal femur measured before surgery.

RESULTS

Bone histology showed significant less osteocyte count in the trabecular bone characterized with smooth and continuous borders in patients with adolescent idiopathic scoliosis. Histomorphometry confirmed the lower static parameters. The results correlated well with the decreased bone mineral density.

CONCLUSION

Bone biopsy study suggested disturbance of bone turnover in patients with adolescent idiopathic scoliosis. The abnormal metabolism might contribute to the low bone mineral density and play an important role in the etiology and pathogenesis of adolescent idiopathic scoliosis.

Bone metabolism and mineral density following renal transplantation

AIM

To study bone turnover following renal transplantation using a panel of biochemical markers and to correlate the results with both areal and volumetric bone mineral density (BMD).

PATIENTS

A total of 31 patients aged 18.1 years were transplanted 5.4 years before this study. Control patients (n = 31) were age and gender matched.

METHODS

In addition to measurement of biochemical markers, BMD was measured by single photon absorptiometry and peripheral quantitative computed tomography on the non-dominant radius.

RESULTS

Patients had reduced glomerular filtration rate, raised concentrations of serum phosphate, serum procollagene type I carboxy terminal propeptide, osteocalcin, and serum procollagene type I cross linked carboxy terminal telopeptide. The differences were still significant if only patients with normal intact parathyroid hormone were considered. BMD single photon absorptiometry Z score for age was significantly decreased. Following standardisation for height the differences were no longer present. With volumetric techniques patients had normal trabecular but decreased cortical and total BMD compared to age matched controls, but there was no difference from height matched controls.

CONCLUSION

Markers of bone turnover are increased following renal transplantation. However, the biochemical analysis did not allow conclusions to be drawn on the bone mineral content. BMD single photon absorptiometry Z score corrected for height and BMD measured by quantitative computed tomography compared to height matched controls were normal in paediatric renal transplantation patients. Height matched controls should be used in both areal and volumetric BMD measurements in states of growth failure.

Bone disease in patients with long-term renal transplantation and normal renal function

Renal osteodystrophy may persist during the early years after renal transplantation. However, information on bone status after a successful long-term renal transplantation is limited. We examined biochemical parameters, bone mineral density (BMD), and bone histomorphometry in 25 asymptomatic men with normal renal function after 7.5 +/- 5.7 years of a renal transplantation. Serum calcium, phosphorus, alkaline phosphatase, and 1,25(OH)(2)D(3) levels and urinary calcium level and cyclic andenosine monophosphate excretion were within normal range in all patients. Serum intact parathyroid hormone (PTH) level was elevated in 11 subjects (133.6 +/- 78 pg/mL) and normal in the other 14 subjects (47.9 +/- 13.6 pg/mL). Mean BMD at the lumbar spine and femoral neck was low in the entire group. However, it progressively increased as time after transplantation increased, approaching normal values after 10 years. Bone histomorphometric analysis showed bone resorption, osteoid volume, and osteoid surface greater than normal range in the majority of patients. Bone formation rate and mineralization surface were low, and mineralization time was delayed in most patients. These lesions were more severe in patients after 3 to 4 years of transplantation but improved with time and approached normal values after a period of 10 years. PTH values did not correlate with bone histological characteristics or BMD. These results show that the bone alterations observed after long-term renal transplantation consist of a mixed bone disease in which features of high bone turnover coexist with altered bone formation and delayed mineralization. These findings may result from the combined effect of preexisting bone disease and immunosuppressive therapy.

High prevalence of low bone turnover and occurrence of osteomalacia after kidney transplantation

Kidney transplantation corrects most of the metabolic abnormalities that cause renal osteodystrophy. However, many transplanted patients develop osteoporosis and other bone lesions that are related, at least in part, to their immunosuppressive regimen. The precise histologic patterns of bone disease after transplantation are not well defined. In a study designed to investigate this issue, 57 adult posttransplant patients agreed to undergo bone biopsies and blood drawings. There were 32 men and 25 women, mean age 45 +/- 2 yr, who had received a kidney transplantation 5.6 +/- 0.8 yr before biopsy. History of bone pain, fractures, and avascular necrosis was found in 22, 12, and 7 patients, respectively. Serum creatinine was 1.68 +/- 0.1 mg/dl, 21% of patients were hypercalcemic, 63.2% had elevated parathyroid hormone (PTH) (>65 pg/ml), and 91.2% had normal calcitriol levels. Cancellous bone volume/tissue volume was below normal compared to age- and gender-matched control subjects in 56.1% of patients. Bone turnover (activation frequency) was low in 45.6%, normal in 28.1%, and elevated in 26.3% of patients. Bone formation rate/bone surface was low in 59.7%, normal in 35%, and elevated in 5. 3% of the patients. Erosion surface/bone surface was high in 21.1% of patients. Mineralization was prolonged in 87.5% of patients, including 9 patients with osteomalacia and 12 patients with focal osteomalacia. Cumulative and maintenance doses of prednisone and time elapsed since transplantation correlated negatively with bone volume and bone turnover (r = -0.32 to -0.59, P < 0.05 to 0.01), whereas cumulative doses of cyclosporine or azathioprine, age, gender, or serum PTH levels did not. Regression analysis identified prednisone as the main factor responsible for low bone volume and bone turnover (r = 0.54 and r = 0.43, P < 0.01). No factors were found to predict delayed mineralization. The present study shows that low bone volume, low bone turnover, and generalized or focal osteomalacia are frequent histologic features in transplanted patients. The effects of age, gender, PTH, and cyclosporine on bone volume and bone turnover are apparently overridden by the prominent effects of glucocorticoids. The prevalence of mineralization defect in the presence of normal serum levels of calcidiol and calcitriol suggests vitamin D resistance and deserves further study.

Normative data for iliac bone histomorphometry in growing children

Many insights into normal and pathologic bone development can only be gained by bone histomorphometry. However, the use of this technique in pediatrics has so far been hampered by the lack of reference data. Therefore, we obtained transfixing iliac bone samples from 58 individuals between 1.5 and 22.9 years of age (25 male; tetracycline labeling performed in 48 subjects), who underwent surgery for reasons independent of abnormalities in bone development and metabolism. The results of histomorphometric analyses of cancellous parameters and cortical width are presented as means and standard deviations, as well as medians and ranges in five age groups. In addition, the original data are available from the authors. There were significant age-dependent increases in both cortical width and cancellous bone volume, the latter being due to an increase in trabecular thickness. Osteoid thickness did not vary significantly with age. Bone surface-based indicators of bone formation showed an age-dependent decline, reflecting similar changes in activation frequency. Mineral apposition rate decreased continuously with age. Parameters of bone resorption did not vary significantly between age groups. Paired biopsies from adjacent sites, obtained in eight subjects, were used to examine the reproducibility of histomorphometric parameters in children. The lowest coefficients of variation (<10%) were found for structural measures, as well as mineral apposition rate and wall thickness. The highest variability was found for cellular parameters. The availability of reference material will greatly facilitate the use of histomorphometry in pediatrics.

Bone loss in long-term renal transplantation: histopathology and densitometry analysis

BACKGROUND

There is little information of the spectrum and factors implicated in the bone loss in long-term renal transplantation, and virtually no data using both histomorphometric and densitometric analysis.

METHODS

Twenty-three males and 22 females (13 postmenopausal) were studied with a bone biopsy and densitometry. Sixteen patients were on cyclosporine A monotherapy, 20 on azathioprine + prednisolone, and 9 on cyclosporine A + prednisolone or triple therapy. The mean time after transplantation was 127 +/- 70 months.

RESULTS

No group had a significant decrease in bone mineral density (BMD) of the axial skeleton compared with an age- and sex-matched normal population. Compared with sex-matched young controls, osteopenia was observed in all groups at the femoral neck (except premenopausal women and triple therapy) and in the triple-therapy group at the L1-L4 spine region. At the distal radius, osteopenia was found in all the groups. Histopathological diagnosis was mixed uremic osteodystrophy in 46.5%, adynamic bone in 23.2%, hyperparathyroid disease in 13.9%, and normal bone in 16.3%. The diagnosis was not different according to immunosuppressive therapy, but men tended to show more mixed uremic bone disease. There was no significant difference in BMD between histopathological subtypes. In general, patients showed slight osteoclast function increase, osteoblast function decrease, and marked retardation of dynamic parameters. The cyclosporine A monotherapy group had a significantly lower appositional rate than azathioprine + prednisolone. Men had a significantly lower bone volume than women, and premenopausal women had a significantly lower mineralizing surface than postmenopausal women and men. In the multivariate analysis, male gender, time after transplantation, old age, and time on dialysis prior to transplantation were significant predictive factors for a negative effect on bone mass.

CONCLUSIONS

Long-term renal transplant-patients showed reduced BMD in both trabecular and cortical bone. This reduction in BMD was not as severe as in short-term reports and was associated with osteoclast stimulation, osteoblast suppression, and retardation of mineral apposition and bone formation rates. Bone mass loss was not different between the immunosuppression therapy groups. Male gender and age were the strongest predictive factors for low bone mass.