Limitations of dual x-ray absorptiometry in children with chronic kidney disease

Mineral bone disorder in children with chronic kidney disease: Data from the KNOW-Ped CKD (Korean cohort study for outcome in patients with pediatric chronic kidney disease) study

BACKGROUND

Children with chronic kidney disease (CKD) are at high risk of mineral bone disorder (MBD), which leads to fractures, growth retardation, and cardiovascular disease. We aimed to comprehensively understand the relationship between renal function and factors related to MBD and evaluate the prevalence and distribution characteristics of MBD, specifically among Korean patients from the KNOW-PedCKD cohort.

METHODS

From the baseline data of the KNOW-PedCKD cohort, we examined the prevalence and distribution of MBD in 431 Korean pediatric CKD patients, including the level of corrected total calcium, serum phosphate, serum alkaline phosphatase, serum intact parathyroid hormone (iPTH), fibroblast growth factor 23 (FGF-23), serum vitamin D, fractional excretion of phosphate (FEP), and bone densitometry Z-scores.

RESULTS

The median serum calcium level remained relatively normal regardless of the CKD stage. The levels of 1,25-dihydroxy vitamin D, urine calcium-to-creatinine ratio, and bone densitometry Z-score significantly decreased with advancing CKD stage, while those of serum phosphate, FGF-23, and FEP significantly increased with CKD stage. The prevalence of hyperphosphatemia (17.4%, 23.7%, and 41.2% from CKD stages 3b, 4, and 5, respectively) and hyperparathyroidism (37.3%, 57.4%, 55.3%, and 52.9% from CKD stages 3a, 3b, 4, and 5, respectively) significantly increased with the CKD stage. Prescriptions of medications, such as calcium supplements (39.1%, 42.1%, 82.4%), phosphate binders (39.1%, 43.4%, 82.4%), and active vitamin D (21.7%, 44.7%, and 64.7%) significantly increased with CKD stage 3b, 4, and 5, respectively.

CONCLUSIONS

The results demonstrated the prevalence and relationship of abnormal mineral metabolism and bone growth according to CKD stage in Korean pediatric CKD patients for the first time.

Pediatric CKD-MBD: existing and emerging treatment approaches

The effects of bone and mineral metabolism on skeletal formation, as well as vascular and soft tissue calcifications, define chronic kidney disease-metabolic bone disease (CKD-MBD). Treatment recommendations center on establishing adequate vitamin D status, phosphate control through diet restriction and phosphate binders, and the use of vitamin D analogs for specific indications. Several emerging bone-promoting therapies have now been studied in adults with CKD, including bisphosphonates and denosumab. These approaches are associated with improved bone mass and, in some cases, decreased fracture rates in adults with CKD-MBD and are of potential interest for some children with CKD-MBD. In children with CKD and immobilization and/or muscle weakness, bisphosphonates appear to be an effective treatment to increase bone mass; baseline assessment and careful monitoring of bone density and/or bone biopsy findings are important in consideration of any new bone therapies for children with CKD-MBD.

Adverse Consequences of Chronic Kidney Disease on Bone Health in Children

Chronic kidney disease (CKD) mineral bone disorder has long-term effects on skeletal integrity and growth. Abnormalities in serum markers of mineral metabolism are evident early in pediatric CKD. Bone deformities, poor linear growth, and high rates of fractures are common in children with CKD. Newer imaging modalities such as high-resolution peripheral quantitative computed tomography shows promise in assessing bone mineral density more comprehensively and predicting incident fractures. A lack of large-scale studies that provide a comprehensive assessment of bone histology and correlations with serum biomarkers has contributed to the absence of evidence-based guidelines and suboptimal management of CKD mineral bone disorder in children with CKD.

"Which skeletal imaging modality is best for assessing bone health in children and young adults compared to DXA? A systematic review and meta-analysis"

BACKGROUND

Skeletal imaging techniques have become clinically valuable methods for measuring and assessing bone mineral density in children and young people. Dual-energy X-ray absorptiometry (DXA) is the current reference standard for evaluating bone density, as recommended by the International Society for Clinical Densitometry (ISCD). Various bone imaging modalities, such as quantitative ultrasound (QUS), peripheral quantitative computed tomography (pQCT), high-resolution peripheral quantitative computed tomography (HR-pQCT), magnetic resonance imaging (MRI), and digital X-ray radiogrammetry (DXR) have been developed to further quantify bone health in children and adults. The purpose of this review, with meta-analysis, was to systematically research the literature to compare the various imaging methods and identify the best modality for assessing bone status in healthy papulations and children and young people with chronic disease (up to 18 years).

METHODS

A systematic computerized search of Medline, PubMed, and Web of Science databases was conducted to identify English-only studies published between 1st January 1990 and 1st December 2019. In this review, clinical studies comparing imaging modalities with DXA were chosen according to the inclusion criteria. The risk of bias and quality of articles was assessed using the Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS-2). The meta-analysis to estimate the overall correlation was performed using a Fisher Z transformation of the correlation coefficient. Additionally, the diagnostic accuracy measures of different imaging methods compared with DXA were calculated.

RESULTS

The initial search strategy identified 13,412 papers, 29 of which matched the inclusion and exclusion criteria. Of these, twenty-two papers were included in the meta-analysis. DXA was compared to QUS in 17 papers, to DXR in 7 and to pQCT in 4 papers. A single paper compared DXA, DXR, and pQCT. The meta-analysis demonstrated that the strongest correlation was between DXR and DXA, with a coefficient of 0.71 [95%CI: 0.43; 1.00, p-value < 0.001], while the correlation coefficients between QUS and DXA, and pQCT and DXA were 0.57 [95%CI: 0.25; 0.90, p-value < 0.001] and 0.57 [95%CI: 0.46; 0.67, p-value < 0.001], respectively. The overall sensitivity and specificity were statistically significant 0.71 and 0.80, respectively.

CONCLUSION

No current imaging modality provides a full evaluation of bone health in children and young adults, with each method having some limitations. Compared to QUS and pQCT, DXR achieved the strongest positive relationship with DXA. DXR should be further evaluated as a reliable method for assessing bone health and as a predictor of fractures in children and young people.

Association between insulin growth factor-1, bone mineral density, and frailty phenotype in children with chronic kidney disease

BACKGROUND

This cohort study investigates the association between insulin growth factor-1 (IGF-1), bone mineral density, and frailty phenotype in children with chronic kidney disease (CKD).

METHODS

Forty-six patients (median age 14.5 years) were prospectively enrolled. Frailty phenotype was defined as the presence ≥ 3 of the following indicators: suboptimal growth/weight gain (body mass index height age < 5th percentile or height < 3rd percentile or loss of ≥ 10 percentiles/year in at least one parameter), low muscle mass (lean tissue mass height age < 5th percentile or loss of ≥ 10 percentiles/year), general fatigue reported by parent or child, and C-reactive protein > 3 mg/l. Lumbar bone mineral apparent density (LBMAD) was measured by dual-energy X-ray absorptiometry, body composition by bioimpedance spectroscopy, and IGF-1 by enzyme-labeled chemiluminescent immunometric assay.

RESULTS

Frailty phenotype (seven patients) was more frequent in advanced CKD (estimated glomerular filtration rate < 30 ml/min/1.73m²) (p = 0.014). IGF-1 and LBMAD z-scores were lower in patients with suboptimal growth/weight gain (14 patients) (p = 0.013, p = 0.012), low muscle mass (nine patients) (p = 0.001, p = 0.009), and general fatigue (eight patients) (p < 0.001, p = 0.004). IFG-1 and LBMAD z-scores were associated with frailty phenotype (OR 0.109, 95% CI 0.015-0.798 and OR 0.277, 95% CI 0.085-0.903) after adjustment for CKD stage. IGF-1 z-score was associated with LBMAD < 5th percentile (six patients) (OR 0.020, 95% CI 0.001-0.450) after adjustment for CKD stage. The association between LBMAD and frailty phenotype lost significance after adjustment for IGF-1.

CONCLUSION

Frailty phenotype is more frequent in advanced pediatric CKD. IGF-1 is negatively associated with frailty phenotype and interferes in the association between frailty and LBMAD.

A prospective case-control pilot study to evaluate bone microarchitecture in children and teenagers on long-term parenteral nutrition using HR-pQCT

Long-term parenteral nutrition (PN) may induce bone complications. Tridimensional bone imaging techniques such as high-resolution peripheral quantitative computed tomography (HR-pQCT) allow the assessment of both compartmental volumetric densities and microarchitecture. Our aim was to evaluate these parameters in children and teenagers receiving long-term PN. This cross-sectional, case–control study included children older than 9 years undergoing PN for at least 2 years. They were age-, gender- and puberty-matched with healthy controls (1:2). Evaluation included biological assessment of bone metabolism (serum calcium, phosphate, and albumin; urinary calcium and creatinine; 25-OH vitamin D, osteocalcin and PTH), dual X-ray absorptiometry (DXA) and HR-pQCT at the ultradistal tibia and radius. Results are presented as median [range]. Eleven patients (3 girls) with a median age of 16 [9–19] years were included. Bone parameters assessed by HR-pQCT at the ultradistal radius and tibia were similar in patients and controls. Parathyroid hormone (PTH) levels were higher (14 [7–115] vs 16 [12–27]) and osteocalcin levels were lower (44 [15–65] vs 65 [38–142]) in patients than in controls, although within the normal range. Conclusions: there were no differences for compartmental bone densities and microarchitecture in patients undergoing chronic PN. Further longitudinal studies are required to confirm these quite reassuring preliminary results.

Routine serum biomarkers, but not dual-energy X-ray absorptiometry, correlate with cortical bone mineral density in children and young adults with chronic kidney disease

Background. Biomarkers and dual-energy X-ray absorptiometry (DXA) are thought to be poor predictors of bone mineral density (BMD). The Kidney Disease: Improving Global Outcomes guidelines suggest using DXA if the results will affect patient management, but this has not been studied in children or young adults in whom bone mineral accretion continues to 30 years of age. We studied the clinical utility of DXA and serum biomarkers against tibial cortical BMD (CortBMD) measured by peripheral quantitative computed tomography, expressed as Z-score CortBMD, which predicts fracture risk.

Methods. This was a cross-sectional multicentre study in 26 patients with CKD4 and 5 and 77 on dialysis.

Results. Significant bone pain that hindered activities of daily living was present in 58%, and 10% had at least one low-trauma fracture. CortBMD and cortical mineral content Z-scores were lower in dialysis compared with CKD patients (P = 0.004 and P = 0.02). DXA BMD hip and lumbar spine Z-scores did not correlate with CortBMD or biomarkers. CortBMD was negatively associated with parathyroid hormone (PTH; r = −0.44, P &lt; 0.0001) and alkaline phosphatase (ALP; r = −0.22, P = 0.03) and positively with calcium (Ca; r = 0.33, P = 0.001). At PTH &lt;3 times upper limit of normal, none of the patients had a CortBMD below −2 SD (odds ratio 95% confidence interval 7.331 to infinity). On multivariable linear regression PTH (β = −0.43 , P &lt; 0.0001), ALP (β = −0.36, P &lt; 0.0001) and Ca (β = 0.21, P = 0.005) together predicted 57% of variability in CortBMD. DXA measures did not improve this model.

Conclusions. Taken together, routinely used biomarkers, PTH, ALP and Ca, but not DXA, are moderate predictors of cortical BMD. DXA is not clinically useful and should not be routinely performed in children and young adults with CKD 4–5D.

Vigier R, Zustin J, Haffner D. Management of bone disease in cystinosis: Statement from an international conference

Cystinosis is an autosomal recessive storage disease due to impaired transport of cystine out of lysosomes. Since the accumulation of intracellular cystine affects all organs and tissues, the management of cystinosis requires a specialized multidisciplinary team consisting of pediatricians, nephrologists, nutritionists, ophthalmologists, endocrinologists, neurologists' geneticists, and orthopedic surgeons. Treatment with cysteamine can delay or prevent most clinical manifestations of cystinosis, except the renal Fanconi syndrome. Virtually all individuals with classical, nephropathic cystinosis suffer from cystinosis metabolic bone disease (CMBD), related to the renal Fanconi syndrome in infancy and progressive chronic kidney disease (CKD) later in life. Manifestations of CMBD include hypophosphatemic rickets in infancy, and renal osteodystrophy associated with CKD resulting in bone deformities, osteomalacia, osteoporosis, fractures, and short stature. Assessment of CMBD involves monitoring growth, leg deformities, blood levels of phosphate, electrolytes, bicarbonate, calcium, and alkaline phosphatase, periodically obtaining bone radiographs, determining levels of critical hormones and vitamins, such as thyroid hormone, parathyroid hormone, 25(OH) vitamin D, and testosterone in males, and surveillance for nonrenal complications of cystinosis such as myopathy. Treatment includes replacement of urinary losses, cystine depletion with oral cysteamine, vitamin D, hormone replacement, physical therapy, and corrective orthopedic surgery. The recommendations in this article came from an expert meeting on CMBD that took place in Salzburg, Austria, in December 2016.

Skeletal status assessment by quantitative ultrasound and bone densitometry in children with different renal conditions

Two methods of skeletal status assessment-quantitative ultrasound (QUS) and densitometry (DXA)-were applied and compared in a group of children with different renal disorders. Skeletal assessments in children with different renal conditions should rather not be based on a single diagnostic tool. Lumbar spine DXA is very effective to reveal disturbances secondary to glucocorticoids, whereas total body DXA and QUS are both better in identification of disturbances related to decreased GFR.

INTRODUCTION

The aim of the study was to evaluate the skeletal status in children in different stages of chronic kidney disease (CKD) or treated with glucocorticoids, using either densitometry (DXA) or quantitative ultrasound (QUS) methods.

METHODS

Seventy-six subjects (27 girls/49 boys) at the mean age of 11.8 ± 4.0 years were enrolled to the reported study. They were divided into three subgroups: with normal glomerular filtration rate (GFR) but treated with glucocorticoids (GCs, n = 38), with decreased GFR (CKD 2-5, n = 26) and with normal GFR and without any bone-toxic treatment (CKD 1, n = 12). DXA scans were carried out at lumbar spine (LS) and at total body (TB), and quantitative ultrasound (QUS) imaging was done at hand phalanges. QUS results were compared to those obtained from 310 healthy matched controls.

RESULTS

The average Z-score for LS-BMD and TB-BMD was below zero in all the study subgroups. Neither were there any significant differences in the mean Z-score for LS among the subgroups. The mean Z-score for TB was significantly the lowest in the CKD 2-5 subgroup. The percentage of subjects with TB Z-score ≤ - 2.0 was the highest in the CKD 2-5 subgroup (69.2%), whereas the percentage of subjects with LS Z-score ≤ - 2.0 was the highest in the GC subgroup (23.7%). QUS results in CKD 2-5 were significantly lower than those in the controls, whereas the results, obtained in GC and CKD 1 subgroups, were similar to those in healthy subjects.

CONCLUSIONS

Skeletal status assessment in children and adolescents with different renal conditions should not be based on single diagnostic approach. DXA scanning, performed at lumbar spine, is potentially more appropriate to reveal disturbances secondary to long-term GC therapy, whereas TB-DXA is highly effective in the identification of skeletal disturbances related to decreased kidney function. QUS at hand phalanges seems to be a useful diagnostic means in CKD with diminished GFR but insufficient to detect GC-related disturbances.

Teenagers and young adults with nephropathic cystinosis display significant bone disease and cortical impairment

BACKGROUND

Bone impairment appears to be a novel complication of nephropathic cystinosis despite cysteamine therapy. Its exact underlying pathophysiology is nevertheless unclear. The objective of this study was to evaluate bone status among patients included in the French Crystobs study.

METHODS

In addition to clinical data, bone status was evaluated using biomarkers (ALP, PTH, 25-D, 1-25D, FGF23), DXA (spine and total body), and high-resolution peripheral quantitative computed tomography (HR-pQCT) at the tibia and radius. Results were compared to age- and gender-matched healthy controls (1:2 basis) from the local reference cohorts.

RESULTS

At a median age of 22.5 (10.2-34.6) years, 10 patients with nephropathic cystinosis were included (2 receiving conservative therapies, 2 undergoing hemodialysis, 6 with a past of renal transplantation); 7 out of 10 patients complained of a bone symptom (past of fracture, bone deformations, and/or bone pain). Biochemicals and spine DXA did not show any significant abnormalities. Using HR-pQCT, significant decreases in cortical parameters (e.g., cortical thickness 850 (520-1100) versus 1225 (480-1680) μm; p < 0.05) and total volumetric bone mineral density (290 (233-360) versus 323 (232-406) mg/cm³; p < 0.05) were observed in cystinotic patients in comparison to controls at the tibia. There were no differences for trabecular parameters. Similar results were observed at the radius.

CONCLUSIONS

In this pilot study, bone impairment (rather cortical than trabecular) is a significant clinical problem in nephropathic cystinosis; 70% of patients displayed significant bone symptoms, during teenage or young adulthood. This new complication should be known by physicians because of its potential dramatic impact on quality of life.

Nephropathic Cystinosis: Symptoms, Treatment, and Perspectives of a Systemic Disease

Cystinosis is a rare autosomal recessive lysosomal storage disorder caused by mutations in the CTNS gene. Main dysfunction is a defective clearance of cystine from lysosomes that leads to accumulation of cystine crystals in every tissue of the body. There are three different forms: infantile nephropathic cystinosis, which is the most common form, juvenile nephropatic, and non-nephropathic cystinosis. Mostly, first symptom in infantile nephropathic cystinosis is renal Fanconi syndrome that occurs within the first year of life. Another prominent symptom is photophobia due to corneal crystal deposition. Cystine depletion therapy with cysteamine delays end-stage renal failure but does not stop progression of the disease. A new cysteamine formulation with delayed-release simplifies the administration schedule but still does not cure cystinosis. Even long-term depletion treatment resulting in bypassing the defective lysosomal transporter cannot reverse Fanconi syndrome. A future perspective offering a curative therapy may be transplantation of CTNS-carrying stem cells that has successfully been performed in mice.

Treatment of Pediatric Chronic Kidney Disease-Mineral and Bone Disorder

PURPOSE OF REVIEW

In this paper, we review the pathogenesis and treatment of chronic kidney disease-mineral and bone disorder (CKD-MBD), especially as it relates to pediatric CKD patients.

RECENT FINDINGS

Disordered regulation of bone and mineral metabolism in CKD may result in fractures, skeletal deformities, and poor growth, which is especially relevant for pediatric CKD patients. Moreover, CKD-MBD may result in extra-skeletal calcification and cardiovascular morbidity. Early increases in fibroblast growth factor 23 (FGF23) levels play a key, primary role in CKD-MBD pathogenesis. Therapeutic approaches in pediatric CKD-MBD aim to minimize complications to the growing skeleton and prevent extra-skeletal calcifications, mainly by addressing hyperphosphatemia and secondary hyperparathyroidism. Ongoing clinical trials are focused on assessing the benefit of FGF23 reduction in CKD. CKD-MBD is a systemic disorder that has significant clinical implications. Treatment of CKD-MBD in children requires special consideration in order to maximize growth, optimize skeletal health, and prevent cardiovascular disease.

Prevalence of vitamin D insufficiency among adolescents and its correlation with bone parameters using high-resolution peripheral quantitative computed tomography

Vitamin D deficiency and insufficiency are highly prevalent among adolescents in Hong Kong, which is a sub-tropical city with ample sunshine. Vitamin D level is significantly correlated with key bone density and bone quality parameters. Further interventional studies are warranted to define the role of vitamin D supplementation for improvement of bone health among adolescents.

INTRODUCTION

The relationship between bone quality parameters and vitamin D (Vit-D) status remains undefined among adolescents. The aims of this study were to evaluate Vit-D status and its association with both bone density and bone quality parameters among adolescents.

METHODS

Three hundred thirty-three girls and 230 boys (12-16 years old) with normal health were recruited in summer and winter separately from local schools. Serum 25(OH) Vit-D level, bone density and quality parameters by Dual Energy X-ray Absorptiometry (DXA) and High-Resolution peripheral Quantitative Computed Tomography (HR-pQCT), dietary calcium intake, and physical activity level were assessed.

RESULTS

Sixty-four point seven percent and 11.4 % of subjects were insufficient [25 ≤ 25(OH)Vit-D ≤ 50 nmol/L] and deficient [25(OH)Vit-D < 25 nmol/L] in Vit-D, respectively. The mean level of serum 25(OH)Vit-D in summer was significantly higher than that in winter (44.7 ± 13.6 and 35.9 ± 12.6 nmol/L, respectively) without obvious gender difference. In girls, areal bone mineral density (aBMD) and bone mineral content (BMC) of bilateral femoral necks, cortical area, cortical thickness, total volumetric bone mineral density (vBMD), and trabecular thickness were significantly correlated with 25(OH)Vit-D levels. In boys, aBMD of bilateral femoral necks, BMC of the dominant femoral neck, cortical area, cortical thickness, total vBMD, trabecular vBMD, BV/TV, and trabecular separation were significantly correlated with 25(OH)Vit-D levels.

CONCLUSION

Vit-D insufficiency was highly prevalent among adolescents in Hong Kong with significant correlation between Vit-D levels and key bone density and bone quality parameters being detected in this study. Given that this is a cross-sectional study and causality relationship cannot be inferred, further interventional studies investigating the role of Vit-D supplementation on improving bone health among adolescents are warranted.

The consequences of pediatric renal transplantation on bone metabolism and growth

PURPOSE OF REVIEW

During childhood, growth retardation, decreased final height and renal osteodystrophy are common complications of chronic kidney disease (CKD). These problems remain present in patients undergoing renal transplantation, even though steroid-sparing strategies are more widely used. In this context, achieving normal height and growth in children after transplantation is a crucial issue for both quality of life and self-esteem. The aim of this review is to provide an overview of pathophysiology of CKD-mineral bone disorder (MBD) in children undergoing renal transplantation and to propose keypoints for its daily management.

RECENT FINDINGS

In adults, calcimimetics are effective for posttransplant hyperparathyroidism, but data are missing in the pediatric population. Fibroblast growth factor 23 levels are associated with increased risk of rejection, but the underlying mechanisms remain unclear. A recent meta-analysis also demonstrated the effectiveness of rhGH therapy in short transplanted children.

SUMMARY

In 2013, the daily clinical management of CKD-MBD in transplanted children should still focus on simple objectives: to optimize renal function, to develop and promote steroid-sparing strategies, to provide optimal nutritional support to maximize final height and avoid bone deformations, to equilibrate calcium/phosphate metabolism so as to provide acceptable bone quality and cardiovascular status, to correct all metabolic and clinical abnormalities that can worsen both bone and growth (mainly metabolic acidosis, anemia and malnutrition), promote good lifestyle habits (adequate calcium intake, regular physical activity, no sodas consumption, no tobacco exposure) and eventually to correct native vitamin D deficiency (target of 25-vitamin D >75 nmol/l).

The evaluation of bone metabolism in children with renal transplantation

This study aims to evaluate BMD and bone biomarkers and to investigate the effects of immunosuppressives on bone disease after RTx. Thirty-three RTR aged 16.7 ± 3.7 yr and healthy controls (n = 32) were enrolled. There was no difference between pre-RTx BMD and BMD at the time of study (45.9 ± 30.9 months after RTx), while both values were lower than controls (p < 0.01 and p < 0.05, respectively). Worst BMD scores were obtained at sixth month after RTx (-0.2 ± 0.9) and best at fourth year (1.4 ± 1.3). 25-hydroxy-(OH) vitamin D and OPG were higher in RTR (p < 0.001). BMD z scores negatively correlated with OPG and cumulative CS doses at the time of study (r = -0.344, p < 0.05 and r = -0.371, p < 0.05, respectively). Regression analysis revealed OPG as the only predictor of BMD (β -0.78, 95% CI -0.004 to -0.013, p < 0.001). The increase in OPG, a significant predictor of BMD, could either be secondary to graft dysfunction or for protection against bone loss. CS doses should be minimized to avoid their untoward effects on bone metabolism.

Longitudinal assessment of bone quality in pediatric patients with chronic kidney disease in relation to treatment modality

Children with chronic kidney disease (CKD) are at high risk of developing impaired bone quality. Our aim was to investigate changes of bone quality in children with CKD in relation to their treatmant using two imaging techniques-dual energy X-ray absorptiometry and quantitative ultraSonography (QUS). Thirty-three patients with CKD (18 boys and 15 girls, mean age 10.37 ± 3.37 years) were evaluated with bone mineral density (BMD) measured by DXA at the lumbar spine and hip and with speed of sound (SOS) measured by QUS at the radius and tibia at the beginning and at the end of the study. The patient cohort consisted of 14 patients with CKD stage 3-4 not treated with dialysis (CKD group), 5 patients on peritoneal dialysis treatment (PD group) and 14 patients after kidney transplantation (RTx group). BMD measurements did not show any significant changes in CKD and PD patients during the study. There was a reduction in BMD measured at the lumbar spine, femoral neck and total hip in RTx patients that was approaching significance. During the 2-year follow-up, SOS measurements at the radius decreased significantly in PD patients, whereas SOS measurements at the tibia significantly improved in RTx patients. No significant changes in QUS parameters were recorded for patients in the CKD group. In conclusion, our study shows that QUS parameters seem to better reflect the state of hyperparathyroidism of renal osteodystrophy as they deteriorate significantly in patients on dialysis and improve after renal transplantation.

Bone structural and mechanical indices in Adolescent Idiopathic Scoliosis evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT)

Adolescent Idiopathic Scoliosis (AIS) is associated with systemic low bone mass. It could persist into adulthood and was shown to be an important prognostic factor for curve progression in AIS. Previous studies were confined to areal bone mineral density (aBMD) measured by Dual-energy X-ray Absorptiometry (DXA) which was a two-dimensional measurement for a three-dimensional structure. This conventional measurement was inadequate to evaluate volumetric bone density and bone quality which are important determinants for bone strength and bone health status as defined in the 2000 NIH consensus statement. High-resolution peripheral quantitative computed tomography (HR-pQCT) was therefore used in this study for three-dimensional evaluation of volumetric bone mineral density and bone micro-architecture as well as estimation of bone strength. In this study, 214 newly diagnosed AIS girls and 187 age and gender-matched normal control aged between 11 and 13years old were recruited for HR-pQCT evaluations on bone geometry, trabecular bone micro-architecture and volumetric BMD (vBMD) at the non-dominant distal radius. We demonstrated that AIS was associated with lower Cortical Bone Area, Cortical Bone vBMD, Trabecular Number and greater Trabecular Separation. With multivariate linear regression analysis and after adjustment for age, dietary calcium intake and physical activity level, the association of AIS with lower Cortical Bone vBMD, lower Trabecular Number and greater Trabecular Separation remained statistically significant. The findings of this study indicated that AIS was associated with an abnormal bone quality profile suggestive of alteration in endocortical modeling, derangement in trabecular bone structure and disturbance in bone mineralization. The cause for these changes and how they are related to the etiopathogenesis of AIS warrant further studies.

Metabolic bone disease after renal transplantation

PURPOSE OF THE REVIEW

Posttransplantation mineral and bone disorder (MBD) is an important issue in the care of children after kidney transplantation (KTx) resulting in increased comorbidity, for example, bone pain, fractures, growth failure, and vascular calcifications. It is distinctly different from common forms of osteoporosis and mainly due to preexisting renal osteodystrophy at the time of KTx, glucocorticoid treatment, and reduced graft function. The purpose of this review is to give an overview of the pathogenesis and treatment of posttransplant MBD in children.

RECENT FINDINGS

Recent studies underline the impact of elevated levels of the phosphaturic hormone fibroblast growth factor-23 on posttransplant MBD. Glucocorticoid treatment results in impairment of bone strength, increased fracture risk, and lack of significant catch up, whereas steroid-sparing protocols allow for a normal adult height in the majority of patients. Whether the latter also improves bone strength remains to be elucidated.

SUMMARY

Therapeutic efforts to reduce MBD after KTx should focus on steroid-sparing immunosuppressive protocols, adequate treatment of alterations of calcium, phosphate and vitamin D metabolism, maintenance of regular physical activity, and preservation of transplant function. Preemptive KTx, that is with no prior dialysis, can prevent progressive vascular calcifications.

Abnormal bone quality versus low bone mineral density in adolescent idiopathic scoliosis: a case-control study with in vivo high-resolution peripheral quantitative computed tomography

BACKGROUND CONTEXT

Adolescent idiopathic scoliosis (AIS) is associated with low bone mass that could persist into early adulthood and is an important prognostic factor for curve progression. Previous studies were confined to areal bone mineral density measurement that was a two-dimensional investigation for a three-dimensional structure. Evaluation of volumetric BMD (vBMD) and other bone quality parameters are important for gaining in-depth understanding of the etiopathogenesis of AIS.

PURPOSE

The objective of this study was to carry out direct in vivo measurement of bone quality in AIS using high-resolution peripheral quantitative computed tomography (HR-pQCT) and compare the correlation of bone quality with osteopenia between AIS and control subjects.

STUDY DESIGN/SETTING

A case-control study.

PATIENT SAMPLE

Newly diagnosed AIS girls (n=112) and non-AIS girls (n=115) between 11 and 13 years.

OUTCOME MEASURES

Areal bone mineral density of bilateral femoral necks and HR-pQCT of the nondominant distal radius were performed.

METHODS

Areal bone mineral density of femoral necks was measured by dual-energy X-ray absorptiometry. Subjects were classified into the osteopenic (Z score less than or equal to -1) and nonosteopenic (Z score more than -1) groups. Bone quality parameters, including bone morphometry, trabecular bone microarchitecture, and vBMD, were measured by HR-pQCT (XtremeCT; Scanco Medical, Zurich, Switzerland).

RESULTS

In AIS, the osteopenic group had lower measurements in cortical area, cortical thickness, average vBMD, compact bone vBMD, trabecular vBMD, trabecular bone volume to tissue volume ratio, and trabecular thickness compared with nonosteopenic AIS subjects. In contrast, among the non-AIS controls, the osteopenic group had lower measurements only in bone morphometry, average vBMD, and compact bone vBMD but not in trabecular vBMD and all other trabecular bone microarchitecture parameters.

CONCLUSIONS

This is the first study using HR-pQCT to compare the correlation of bone quality with osteopenia in AIS and non-AIS subjects. It provides new insights and highlights the unique bone quality profile with predominant changes in the trabecular compartment in association with osteopenia being notably only detected in the AIS subjects. Further studies in this area are warranted for defining the metabolic nature and biomechanical sequelae of derangement in bone mass and bone quality and their roles in the etiopathogenesis of AIS.

A two-yr prospective study of bone health in children after renal transplantation employing two imaging techniques

The aim of this study was to prospectively and longitudinally evaluate bone properties with the use of two bone imaging techniques (dual energy X-ray absorptiometry [DXA], and quantitative ultraSonography [QUS]) in pediatric renal transplant recipients. Fourteen patients (eight boys and six girls) with a mean age of 12.25 ± 3.11 yr (range: 8-17.5 yr) completed a two-yr follow-up. Measurements of bone mineral density (BMD) by DXA at lumbar spine and hip and speed of sound (SOS) by QUS at radius and tibia were performed at the beginning and at the end of the study. A significant improvement in mean Z-score of SOS values measured at tibia (1.01 ± 1.31 vs. -0.46 ± 1.14, p = 0.005) was observed. On the contrary, mean Z-score of BMD values measured at femoral neck was significantly reduced (-1.95 ± 2.15 vs. -0.33 ± 1.13, p = 0.041). Finally, multivariate stepwise regression analyses showed that glomerular filtration rate at the beginning of the study was the best predictor of the difference in BMD Z-scores measured at lumbar spine. Additionally, values of intact parathormone (iPTH) at the beginning of the study and the change in iPTH throughout the study predicted the 72.3% of the difference in Z-score of SOS measured at radius with an inverse relationship.

Skeletal effects and growth in children with chronic kidney disease: a 5-year prospective study

This study was designed to follow the evolving process of growth, bone modeling and remodeling in children with chronic kidney disease (CKD) who are at risk of developing CKD-mineral bone disorder (CKD-MBD). Fifteen patients, 4-15 years, were included with a median glomerular filtration rate of 46 (range 12-74) mL/min/1.73 m(2). Growth, bone mineral density (BMD) and markers of bone and mineral metabolism were investigated over a 5-year period. The median height standard deviation score was -0.65 at the start and 0.1 after 5 years, with a range from -1.7 to 1.7, which implies that growth was acceptable. Total body, femoral neck, and lumbar spine BMD increased over the study period (p < 0.0001). None had total body BMD Z-scores and lumbar spine Z-scores below -2.0 at follow-up. Most bone markers were within the reference intervals, but the formation markers of alkaline phosphatase and type I procollagen intact amino-terminal propeptide (PINP) were slightly increased in about one-third of the patients after 5 years. Eleven out of 15 CKD patients had increased parathyroid hormone levels at baseline and 10 patients after 5 years had increased parathyroid hormone levels. Taken together, this is the first 5-year longitudinal study of skeletal effects, growth and bone turnover in children with CKD. Growth and BMD Z-scores were well preserved on a group basis; however, these parameters varied significantly on an individual basis. We suggest, therefore, that it is difficult to state an overall recommendation and growth, bone mass, and markers of bone and mineral metabolism should be monitored and treated individually in CKD children.

Idiopathic juvenile osteoporosis: a cross-sectional single-centre experience with bone histomorphometry and quantitative computed tomography

BACKGROUND

Idiopathic juvenile osteoporosis (IJO) is a rare condition of poorly understood etiology and pathophysiology that affects otherwise healthy children. This condition is characterized clinically by bone pain and vertebral fractures; spontaneous recovery is observed after puberty in the majority of cases. Although decreased trabecular bone turnover has been noted previously, cortical and trabecular bone characteristics as determined by quantitative computed tomography (QCT) and their relationship to bone histomorphometry are unknown.

METHODS

All children with a clinical diagnosis of IJO who were followed in our center since 1995 and who had undergone at least one diagnostic bone biopsy were included in this cross-sectional analysis.

RESULTS

Fifteen patients (11 males/4 females) with median ages of 5.8 and 10.2 years at first symptoms and at referral, respectively, were included in the analysis. Histomorphometric analysis demonstrated decreased trabecular bone turnover (BFR/BS) in the majority of patients with heterogeneous parameters of trabecular mineralization and volume. QCTresults demonstrated that bone mineral density (BMD) was reduced in both trabecular/lumbar and cortical/femoral bone: Z score: -2.1 (-3.6;-1.0) and -0.9 (-8.2;1.4)in the two compartments, respectively. In the eight patients who underwent both bone biopsy and QCT, cortical BMD was associated with trabecular separation and with trabecular bone formation rate (r = 0.898 and -0.881, respectively, both p < 0.05).

CONCLUSIONS

This series confirms that IJO is characterized by impaired trabecular architecture that can be detected by both bone biopsy and QCT. The association between bone biopsy and QCT results may have implications for diagnosis, treatment, and follow-up of these children.

Anatomically reproducible assessment of volumetric bone mineral density--based on clinical computed tomography

Local distribution and quality of bone mineral density (BMD) in the proximal humerus are important for rotator cuff repair, internal fixations, and arthroplasty. The current study aimed to develop a volumetric BMD (vBMD) measurement technique that can specify the volumetric region of interest in an anatomically reproducible manner and ensures fair comparison of vBMD among intrasubjective or intersubjective measurements. Computed toed into three-dimensional (3D) polygon models. A standardized volumetric block was asmographic images of 10 intact shoulders (from six women and four men, age range 46-69 years) were reconstruct signed, and it included whole insertion areas of the supraspinatus and infraspinatus tendons on the greater tuberosity. For standardizing a bone block, a mathematical method for reproducible landmark assignment and reproducible local coordinate system was developed. After converting the polygonal standardized volumetric block into 3D tetrahedron finite element models, its vBMD was calculated. The repeatability and reproducibility standard deviations of the vBMD measurement method were found to be less than 2%. The current study developed a vBMD measurement technique that can specify the vROI in an anatomically reproducible manner and ensures fair comparison of BMD among intrasubjective or intersubjective measurements, with less than 2% reproducibility error.

The consequences of chronic kidney disease on bone metabolism and growth in children

Growth retardation, decreased final height and renal osteodystrophy (ROD) are common complications of childhood chronic kidney disease (CKD), resulting from a combination of abnormalities in the growth hormone (GH) axis, vitamin D deficiency, hyperparathyroidism, hypogonadism, inadequate nutrition, cachexia and drug toxicity. The impact of CKD-associated bone and mineral disorders (CKD-MBD) may be immediate (serum phosphate/calcium disequilibrium) or delayed (poor growth, ROD, fractures, vascular calcifications, increased morbidity and mortality). In 2012, the clinical management of CKD-MBD in children needs to focus on three main objectives: (i) to provide an optimal growth in order to maximize the final height with an early management with recombinant GH therapy when required, (ii) to equilibrate calcium/phosphate metabolism so as to obtain acceptable bone quality and cardiovascular status and (iii) to correct all metabolic and clinical abnormalities that can worsen bone disease, growth and cardiovascular disease, i.e. metabolic acidosis, anaemia, malnutrition and 25(OH)vitamin D deficiency. The aim of this review is to provide an overview of the mineral, bone and vascular abnormalities associated with CKD in children in terms of pathophysiology, diagnosis and clinical management.

Can bisphosphonates play a role in the treatment of children with chronic kidney disease?

In patients with chronic kidney disease (CKD) renal osteodystrophy, in the form of either low- or high-turnover bone disease, is quite common. While renal transplantation is expected to reverse renal osteodystrophy, long-term treatment with glucocorticoids before and/or after transplantation may lead to osteoporosis instead. Osteoporosis is defined as a skeletal disease with low bone mineral density, microarchitectural deterioration, and concomitant fragility. In adults, bisphosphonates are widely used to treat osteoporosis and other diseases associated with excessive bone resorption. In pediatric CKD patients the efficacy and safety of these drugs have not yet been addressed adequately and thus no evidence-based recommendations regarding the optimal type of bisphosphonate, dosage, or duration of therapy are available. Furthermore, while in adults the determination of areal bone mineral density is sufficient to diagnose osteoporosis, this is not the case in children. Instead, in pediatric patients, careful morphological assessment of bone structure and formation is required. Indeed, data from studies with uremic rats indicated that bisphosphonates, via a deceleration of bone turnover, have the potential not only to aggravate pre-existing adynamic bone disease, but also to impair longitudinal growth. Thus, the widespread use of bisphosphonates in children with CKD should be discouraged until the risks and benefits have been carefully elucidated in clinical trials.

Mineral and bone disorders in children with chronic kidney disease

As children with chronic kidney disease (CKD) have a long lifespan, optimal control of bone and mineral homeostasis is essential not only for the prevention of debilitating skeletal complications and for achieving adequate growth but also for preserving long-term cardiovascular health. As the growing skeleton is highly dynamic and at particular risk of deterioration, close control of bone and mineral homeostasis is required in children with CKD. However, assessment of bone disease is hampered by the limited validity of biochemical parameters-major controversy exists on key issues such as parathyroid hormone target ranges and the lack of useful imaging techniques. The role of newly discovered factors in bone and mineral homeostasis, such as fibroblast growth factor 23, is not yet established. Even though scientific evidence is limited in children with CKD, ergocalciferol or cholecalciferol supplementation and the use of calcium-free phosphate binders is recommended. The new drug cinacalcet is highly promising; however, pediatric experience is still limited to observational data and the effect of cinacalcet on longitudinal growth and pubertal development is unknown. Randomized, controlled trials are underway, including studies of cinacalcet pharmacokinetics and pharmacodynamics in infants.

Bone mineral disorders in pediatric and adolescent renal transplant recipients

Incomplete resolution of abnormalities of mineral metabolism associated with CRF results in the relatively high prevalence of ROD in pediatric kidney recipients. This non-randomized, cross-sectional, and analytic-descriptive study on bone density, vitamin D, and mineral metabolism was performed in 57 children and adolescents who had received a total of 60 renal allografts in Shiraz, Iran. The height and weight of the patients were measured; their serum calcium (Ca), phosphorus (P), Alk-P, PTH, 25(OH)-vitamin D(3), BUN, creatinine, and electrolyte levels were analyzed, and a complete blood count was performed. In addition, standard radiologic bone assessments, which included conventional left hand-wrist radiography and bone mineral densitometry by the DXA technique, were carried out. Special pediatric software was used for age-related interpretation of the Z-scores of BMD. SPSS(®) software (version 15) was used for statistical analyses. We studied 57 patients (27 males [47.4%]) with a mean age of 18.7 ± 4.25 (9-27) yr and a mean age at transplantation of 13.1 ± 3.46 (4.5-20) yr. They had a post-transplantation follow-up of 67.1 ± 33.8 (6-132) months, and all had well-functioning allografts at enrollment. The mean height age of the patients was 11.9 ± 1.8 (6-15.5), and the mean bone age was 15.6 ± 3.3 (7-19) yr, which corresponded to mean height-age and bone-age retardations of 5.7 ± 2.3 (0.5-10.5) and 1.22 ± 1.47 (0-7) yr, respectively. Hyperphosphatemia and hypercalcemia were each found in nine patients (15.8%), hypophosphatemia in five (8.8%), and hypocalcemia in none of the patients. Seven out of 57 patients (12.3%) had a (Ca×P) product of more than 55 mg(2)/dL(2). Hyperparathyroidism was found in 27 (47.3%) and vitamin D(3) deficiency in four (7%) of the cases. The serum level of Alk-P was higher than the age-related normal range in 20 patients (35%). Left hand-wrist radiography showed no radiologic sign of ROD in any patient. The mean BMD Z-score was -1.77 ± 1.13 (-4.2-1.1) for the lumbar spine and -1.64 ± 0.89 (-3.9 to 1.9) for the femoral neck. "Stepwise backward regression" revealed a significant inverse correlation between the serum level of PTH and the GFR of the transplanted kidney; this correlation was independent from the influence of other variables such as Ca, P, and Alk-P (p = 0.011, β = -1.556). Bone age and height age both showed significant correlations with age at transplantation and serum levels of P (p < 0.001), but only bone age had a meaningful correlation with Alk-P (p = 0.036). The BMD Z-scores showed statistically meaningful correlations with the serum level of Alk-P, which were independent from the influence of other variables such as Ca, P, and PTH (p ≤ 0.002). Our study revealed a relatively high prevalence of bone mineral disorder in pediatric kidney recipients, which suggests the need for a routine program for periodic screening of these patients to facilitate early diagnosis of either persistent or evolving manifestations of disturbed mineral metabolism, especially ROD.

Comparative study of quantitative ultrasonography and dual-energy X-ray absorptiometry for evaluating renal osteodystrophy in children with chronic kidney disease

Our aim was to assess bone parameters in children with chronic kidney disease (CKD) with both dual-energy X-ray absorptiometry (DXA) and quantitative ultrasonography (QUS) and additionally with biochemical markers of bone turnover. Twenty children (12 boys and 8 girls) with CKD and a mean decimal age of 9.47 ± 4.44 years were included in the study where anthropometric parameters (height and weight), pubertal status, bone mineral density (BMD) at lumbar spine, speed of sound (SOS) measured by QUS at radius and at tibia, and biochemical markers of bone metabolism were measured. Six patients (30%) had tibial SOS Z score <-1, and 52.7% had radial SOS Z score <-1, whereas only 16.67% had BMD Z score <-1. Patients had significantly increased levels of serum intact parathormone (p < 0.001), serum bone alkaline phosphatase (BAP) (p < 0.001) and serum N-terminal-mid fragment (aminoacids 1-43) of osteocalcin (p < 0.001) compared to controls, whereas serum osteoprotegerin was significantly decreased in patients compared to controls (p = 0.001). SOS was significantly correlated to BAP (r = -0.586, p = 0.013 and r = -0.709, p = 0.001, respectively, for radius and tibia). In conclusion no association between DXA and QUS measurements was documented in our study, whereas QUS was better correlated to biochemical indices of ROD.

Bone assessment in children with chronic kidney disease: data from two new bone imaging techniques in a single-center pilot study

Bone damage in children with chronic kidney disease (CKD) is a challenge for pediatric nephrologists. Areal measurements of bone mineral density (BMD) by dual x-ray absorptiometry (DXA) have been routinely performed to assess bone mass but recent international guidelines have concluded that DXA was of less value in CKD. The aim of this study is to evaluate bone quality in CKD children using new bone imaging techniques in a pilot cross-sectional single-center study. We performed bone imaging (high-resolution peripheral quantitative computed tomography, HR-pQCT, XtremeCT, Scanco Medical AG, Switzerland), to assess compartmental volumetric BMD and trabecular microarchitecture in 22 CKD children and 19 controls. In seven younger patients (i.e., under 10 years of age), we performed bone texture analysis (BMA, D3A Medical Systems, France) in comparison to 15 healthy prepubertal controls. Among older children, CKD patients had significantly lower height and body weight without significant impairment of BMD and microarchitecture than healthy controls. In univariate analysis, there were significant correlations between cortical BMD and glomerular filtration rate (r= -0.46), age (r=0.60) and body mass index (r=0.67). In younger children, bone texture parameters were not different between patients and controls. Our results did not show significant differences between healthy controls and CKD children for compartmental bone densities and microarchitecture, but the small sample size and the heterogeneity of the CKD group require caution in the interpretation. Novel bone imaging techniques seem feasible in children, and further longitudinal studies are required to thoroughly explore long-term cardiovascular and bone consequences of phosphate-calcium metabolism deregulation during CKD.

CKD-MBD after kidney transplantation

Successful kidney transplantation corrects many of the metabolic abnormalities associated with chronic kidney disease (CKD); however, skeletal and cardiovascular morbidity remain prevalent in pediatric kidney transplant recipients and current recommendations from the Kidney Disease Improving Global Outcomes (KDIGO) working group suggest that bone disease-including turnover, mineralization, volume, linear growth, and strength-as well as cardiovascular disease be evaluated in all patients with CKD. Although few studies have examined bone histology after renal transplantation, current data suggest that bone turnover and mineralization are altered in the majority of patients and that biochemical parameters are poor predictors of bone histology in this population. Dual energy X-ray absorptiometry (DXA) scanning, although widely performed, has significant limitations in the pediatric transplant population and values have not been shown to correlate with fracture risk; thus, DXA is not recommended as a tool for the assessment of bone density. Newer imaging techniques, including computed tomography (quantitative CT (QCT), peripheral QCT (pQCT), high resolution pQCT (HR-pQCT) and magnetic resonance imaging (MRI)), which provide volumetric assessments of bone density and are able to discriminate bone microarchitecture, show promise in the assessment of bone strength; however, future studies are needed to define the value of these techniques in the diagnosis and treatment of renal osteodystrophy in pediatric renal transplant recipients.

Infrared spectroscopy indicates altered bone turnover and remodeling activity in renal osteodystrophy

Renal osteodystrophy alters metabolic activity and remodeling rate of bone and also may lead to different bone composition. The objective of this study was to characterize the composition of bone in high-turnover renal osteodystrophy patients by means of Fourier transform infrared spectroscopic imaging (FTIRI). Iliac crest biopsies from healthy bone (n = 11) and patients with renal osteodystrophy (ROD, n = 11) were used in this study. The ROD samples were from patients with hyperparathyroid disease. By using FTIRI, phosphate-to-amide I ratio (mineral-to-matrix ratio), carbonate-to-phosphate ratio, and carbonate-to-amide I ratio (turnover rate/remodeling activity), as well as the collagen cross-link ratio (collagen maturity), were quantified. Histomorphometric analyses were conducted for comparison. The ROD samples showed significantly lower carbonate-to-phosphate (p < .01) and carbonate-to-amide I (p < .001) ratios. The spatial variation across the trabeculae highlighted a significantly lower degree of mineralization (p < .05) at the edges of the trabeculae in the ROD samples than in normal bone. Statistically significant linear correlations were found between histomorphometric parameters related to bone-remodeling activity and number of bone cells and FTIRI-calculated parameters based on carbonate-to-phosphate and carbonate-to-amide I ratios. Hence the results suggested that FTIRI parameters related to carbonate may be indicative of turnover and remodeling rate of bone.