Mineralized bone loss at different sites in dialysis patients: implications for prevention

Mixed uremic osteodystrophy: an ill-described common bone pathology in patients with chronic kidney disease

Renal osteodystrophy (ROD) starts early and progresses with further loss of kidney function in patients with chronic kidney disease (CKD). There are four distinct types of ROD based on undecalcified bone biopsy results. Adynamic bone disease and osteomalacia are the predominant forms of low bone turnover, while hyperparathyroid bone disease and mixed uremic osteodystrophy (MUO) are typically associated with high bone turnover. MUO is a prevalent but poorly described pathology that demonstrates evidence of osteomalacia on top of the high bone formation/resorption. The prevalence of MUO ranges from 5 to 63% among different studies. The pathogenesis of MUO is multi-factorial. Altered phosphate homeostasis, hypocalcemia, vitamin D deficiency, increased FGF-23, interleukins 1 and 6, TNF-α, amyloid, and heavy metal accumulation are the main inducers of MUO. The clinical findings of MUO are usually non-specific. The use of non-invasive testing such as bone turnover markers and imaging techniques might help to suspect MUO. However, it is usually impossible to precisely diagnose this condition without performing bone biopsy. The principal management of MUO is to control the maladaptive hyperparathyroidism along with correcting any nutritional mineral deficiencies that may induce mineralization defect. MUO is a common but still poorly understood bone pathology category; it demonstrates the complexity and difficulty in understanding ROD. A large prospective bone biopsy-based studies are needed for better identification as proper diagnosis and management would improve the outcome of patients with MUO.

Renal hyperparathyroidism

The number of the patients with chronic kidney disease is now increasing in the world. The pathophysiology of renal hyperparathyroidism is closely associated with Klotho-FGF-endocrine axes, which must be solved definitively as early as possible. It was revealed that the expression of fgf23 is activated by calciprotein particles, which induces vascular ossification. And it is well known that phosphorus overload directly increases parathyroid hormone and hyperparathyroid bone disease develops in those subjects. On the other hand, low turnover bone disease is often recently. Both the patients with chronic kidney disease suffering from hyperparathyroid bone disease or low turnover bone disease are associated with increased fracture risk. Micropetrosis may be one of the causes of increased fracture risk in the subjects with low turnover bone disease. In this chapter, we now describe the diagnosis, pathophysiology and treatments of renal hyperparathyroidism.

Micropetrosis in hemodialysis patients

Micropetrosis develops as a result of stagnation of calcium, phosphorus and bone fluid, which appears as highly mineralized bone area in the osteocytic perilacunar/canalicular system regardless of bone turnover of the patients. And microcracks are predisposed to increase in these areas, which leads to increased bone fragility. However, micropetrosis of hemodialysis (HD) patients has not been discussed at all. Micropetrosis area per bone area (Mp.Ar/B·Ar) and osteocyte number per micropetrosis area (Ot.N/Mp.Ar) were measured in nine HD patients with renal hyperparathyroidism (Group I), twelve patients with hypoparathyroidism within 1 year after the treatment of renal hyperparathyroidism (Group II) and seven patients suffering from hypoparathyroidism for over two years (Group III). And bone mineral density (BMD) and tissue mineral density (TMD) were calculated using μCT to evaluate bone mineral content of iliac bone of the patients. These parameters were compared among the three groups. Only Mp.Ar/B·Ar was statistically greater in Group II and III compared to Group I in the parameters of bone mineral content and micropetrosis. However, the other parameters were not statistically different among the three groups. In long-term HD patients, BMD and TMD may be modified by the causes of renal insufficiency and the treatment of renal bone disease. We concluded that Mp.Ar/B·Ar was greater in patients with long-term hypoparathyroidism than both those with short-term hypoparathyroidism and with renal hyperparathyroidism. Special attention should be paid to avoid long-term hypoparathyroidism of the patients from the view point of increased fracture risk caused by increased micropetrosis area.

Predictive value of quantitative ultrasound parameters in individuals with chronic kidney disease: A population-based analysis of CARTaGENE

BACKGROUND

The use of calcaneal quantitative ultrasound (QUS) to predict fractures has not been well studied in early CKD populations. We compared the association of QUS with incidental fractures and its predictive properties in non-CKD and CKD individuals.

METHODS

Analysis of a prospective population-based survey of 40- to 69-year-old individuals recruited between 2009 and 2010. QUS parameters (stiffness index [SI], speed of sound [SOS], broadband attenuation [BUA]) were measured at baseline. Renal function was measured using baseline creatinine and was classified into CKD stages (non-CKD, stage 2, stage 3). Fracture incidence at any site or at major osteoporotic fracture sites for up to 7 years of follow-up was identified in administrative databases using a validated algorithm. The association (age-adjusted hazard ratio per standard deviation decrease in Cox models), discrimination (c-statistic) and calibration (standardized incidence ratio [SIR]) of QUS parameters with fracture outcomes was computed in each CKD stratum.

RESULTS

We included 18,306 individuals (9,011 non-CKD; 8,595 CKD stage 2; 700 CKD stage 3). During a median follow-up of 70 months, we identified 782 fractures at any site and 326 major osteoporotic fractures. Although all QUS parameters (SI, SOS and BUA) were associated with any or major fracture incidence in non-CKD and CKD patients, the magnitude of these associations was lower for any fracture and for BUA. QUS parameters moderately discriminated incidental fractures across CKD strata but underestimated fracture incidence in CKD stage 3 even after adjustment for demographics and clinical risk factors. At a given QUS value, CKD stage 3 patients had higher fracture risk than non-CKD and CKD stage 2 patients.

CONCLUSIONS

QUS parameters are associated with fracture incidence in both non-CKD and CKD but underestimate fracture incidence in individuals with early CKD.

The Importance of Biologically Active Vitamin D for Mineralization by Osteocytes After Parathyroidectomy for Renal Hyperparathyroidism

Hypomineralized matrix is a factor determining bone mineral density. Increased perilacunar hypomineralized bone area is caused by reduced mineralization by osteocytes. The importance of vitamin D in the mineralization by osteocytes was investigated in hemodialysis patients who underwent total parathyroidectomy (PTX) with immediate autotransplantation of diffuse hyperplastic parathyroid tissue. No previous reports on this subject exist. The study was conducted in 19 patients with renal hyperparathyroidism treated with PTX. In 15 patients, the serum calcium levels were maintained by subsequent administration of alfacalcidol (2.0 μg/day), i.v. calcium gluconate, and oral calcium carbonate for 4 weeks after PTX (group I). This was followed in a subset of 4 patients in group I by a reduced dose of 0.5 μg/day until 1 year following PTX; this was defined as group II. In the remaining 4 patients, who were not in group I, the serum calcium (Ca) levels were maintained without subsequent administration of alfacalcidol (group III). Transiliac bone biopsy specimens were obtained in all groups before and 3 or 4 weeks after PTX to evaluate the change of the hypomineralized bone area. In addition, patients from group II underwent a third bone biopsy 1 year following PTX. A significant decrease of perilacunar hypomineralized bone area was observed 3 or 4 weeks after PTX in all group I and II patients. The area was increased again in the group II patients 1 year following PTX. In group III patients, an increase of the hypomineralized bone area was observed 4 weeks after PTX. The maintenance of a proper dose of vitamin D is necessary for mineralization by osteocytes, which is important to increase bone mineral density after PTX for renal hyperparathyroidism. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

A multi-imaging modality study of bone density, bone structure and the muscle - bone unit in end-stage renal disease

End stage renal disease (ESRD) is associated with sarcopenia and skeletal fragility. The objectives of this cross-sectional study were to (1) characterize body composition, bone mineral density (BMD) and bone structure in hemodialysis patients compared with controls, (2) assess whether DXA areal BMD (aBMD) correlates with peripheral quantitative CT (pQCT) measures of volumetric BMD (vBMD), cortical dimensions and MRI measures of trabecular microarchitecture, and (3) determine the magnitude of bone deficits in ESRD after adjustment for muscle mass. Thirty ESRD participants, ages 25 to 64 years, were compared with 403 controls for DXA and pQCT outcomes and 104 controls for MRI outcomes; results were expressed as race- and sex- specific Z-scores relative to age. DXA appendicular lean mass index (ALMI kg/m2) and total hip, femoral neck, ultradistal and 1/3rd radius aBMD were significantly lower in ESRD, vs. controls (all p < 0.01). pQCT trabecular vBMD (p < 0.01), cortical vBMD (p < 0.001) and cortical thickness (due to a greater endosteal circumference, p < 0.02) and MRI measures of trabecular number, trabecular thickness, and whole bone stiffness were lower (all p < 0.01) in ESRD, vs. controls. ALMI was positively associated with total hip, femoral neck, ultradistal radius and 1/3rd radius aBMD and with tibia cortical thickness (R = 0.46 to 0.64). Adjustment for ALMI significantly attenuated bone deficits at these sites: e.g. mean femoral neck aBMD was 0.79 SD lower in ESRD, compared with controls and this was attenuated to 0.33 with adjustment for ALMI. In multivariate models within the dialysis participants, pQCT trabecular vBMD and cortical area Z-scores were significant and independently (all p < 0.02) associated with DXA femoral neck, total hip, and ultradistal radius aBMD Z-scores. Cortical vBMD (p = 0.01) and cortical area (p < 0.001) Z-scores were significantly and independently associated with 1/3rd radius areal aBMD Z-scores (R2 = 0.62). These data demonstrate that DXA aBMD captures deficits in trabecular and cortical vBMD and cortical area. The strong associations with ALMI, as an index of skeletal muscle, highlight the importance of considering the role of sarcopenia in skeletal fragility in patients with ESRD.

Symptomatic fracture risk in the renal replacement therapy population

Background

Bone fractures are an important cause of morbidity and mortality in patients on renal replacement therapy (RRT). The aim of this multicentre observational study was to quantify the incidence of radiologically proven bone fracture by anatomical site in prevalent RRT groups and study its relationship to potential risk factors.

Methods

We performed a retrospective analysis of electronic records of all 2096 adults prevalent on RRT in the West of Scotland on 7 July 2010 across all hospitals (except one where inception was 1 August 2011) to identify all subsequent radiologically proven fractures during a median 3-year follow-up.

Results

There were 340 fractures, with an incidence of 62.8 per 1000 patient-years. The incidences were 37.6, 99.2 and 57.6 per 1000 patient-years in the transplant, haemodialysis (HD) and peritoneal dialysis (PD) groups, respectively (P < 0.05). In the multivariable model, age and HD (relative to transplant or PD) were independently associated with increased risk of fractures, while primary glomerular disease, increasing serum albumin and taking alfacalcidol or lanthanum were associated with decreased risk. In a multivariable model of only HD patients, age was independently associated with an increased risk of fractures, while glomerular disease, high serum albumin and being on alfacalcidol and lanthanum were associated with decreased risk. In a multivariable model in transplant patients, there were no significant independent predictors of fracture.

Conclusions

The risk of symptomatic bone fracture is high in RRT patients and is ∼2.5 times higher in HD than in renal transplant patients, with the increased risk being independent of baseline factors. Fracture risk increases with age and lower serum albumin and is reduced if the primary renal diagnosis is glomerular disease. The possible protective role of alfacalcidol and lanthanum in HD patients deserves further exploration.

Skeletal manifestations of renal disease in childhood

PURPOSE OF REVIEW

This review summarizes recent findings on musculoskeletal health in three chronic renal conditions of childhood: chronic kidney disease stages 2-5D, nephrotic syndrome, and urolithiasis. Findings with important clinical implications warranting further investigation are highlighted.

RECENT FINDINGS

Recent cohort studies have demonstrated a high burden of fracture and progressive deficits of cortical bone in children with chronic kidney disease. Lower cortical density is associated with incident fracture and may be an important therapeutic target. Parathyroid hormone and calcium are independent correlates of cortical density, and modifiable factors for fracture include parathyroid hormone and phosphate binder use. Children with nephrotic syndrome, even with normal renal function, have evidence of abnormal bone metabolism and structure, and vitamin D deficiency may be an important modifiable risk factor in this population. Urolithiasis has been associated with reduced bone mineral density and is increasingly common in children and adolescents. Population-based data found a significantly increased risk of fracture in adolescent males and young women.

SUMMARY

Recent findings substantiate concern regarding the particular vulnerability of the growing skeleton to chronic renal disease. Studies are needed to determine how to optimize assessment and management of bone health in children with these conditions, particularly in terms of calcium and vitamin D requirements, with the goal of improving childhood bone accrual for lifelong fracture prevention.

An update on bone imaging and markers in chronic kidney disease

Bone disorders in chronic kidney disease (CKD) are associated with heightened risks of fractures, vascular calcification, poor quality of life and mortality compared to the general population. However, diagnosis and management of these disorders in CKD are complex and appreciably limited by current diagnostic modalities. Areas covered: Bone histomorphometry remains the gold standard for diagnosis but is not widely utilised and lacks feasibility as a monitoring tool. In practice, non-invasive imaging and biochemical markers are preferred to guide therapeutic decisions. Expert commentary: This review aims to summarize the risk factors for, and spectrum of bone disease in CKD, as well as appraise the clinical utility of dual energy X-ray densitometry, peripheral quantitative computed tomography, high-resolution peripheral quantitative computed tomography, and bone turnover markers.

Phosphate Binding with Sevelamer Preserves Mechanical Competence of Bone Despite Acidosis in Advanced Experimental Renal Insufficiency

Introduction

Phosphate binding with sevelamer can ameliorate detrimental histomorphometric changes of bone in chronic renal insufficiency (CRI). Here we explored the effects of sevelamer-HCl treatment on bone strength and structure in experimental CRI.

Methods

Forty-eight 8-week-old rats were assigned to surgical 5/6 nephrectomy (CRI) or renal decapsulation (Sham). After 14 weeks of disease progression, the rats were allocated to untreated and sevelamer-treated (3% in chow) groups for 9 weeks. Then the animals were sacrificed, plasma samples collected, and femora excised for structural analysis (biomechanical testing, quantitative computed tomography).

Results

Sevelamer-HCl significantly reduced blood pH, and final creatinine clearance in the CRI groups ranged 30%-50% of that in the Sham group. Final plasma phosphate increased 2.4- to 2.9-fold, and parathyroid hormone 13- to 21-fold in CRI rats, with no difference between sevelamer-treated and untreated animals. In the femoral midshaft, CRI reduced cortical bone mineral density (-3%) and breaking load (-15%) (p<0.05 for all versus Sham), while sevelamer increased bone mineral density (+2%) and prevented the deleterious changes in bone. In the femoral neck, CRI reduced bone mineral density (-11%) and breaking load (-10%), while sevelamer prevented the decrease in bone mineral density (+6%) so that breaking load did not differ from controls.

Conclusions

In this model of stage 3–4 CRI, sevelamer-HCl treatment ameliorated the decreases in femoral midshaft and neck mineral density, and restored bone strength despite prevailing acidosis. Therefore, treatment with sevelamer can efficiently preserve mechanical competence of bone in CRI.

Chronic Kidney Disease Impairs Bone Defect Healing in Rats

Chronic kidney disease (CKD) has been regarded as a risk for bone health. The aim of this study was to evaluate the effect of CKD on bone defect repair in rats. Uremia was induced by subtotal renal ablation, and serum levels of BUN and PTH were significantly elevated four weeks after the second renal surgery. Calvarial defects of 5-mm diameter were created and implanted with or without deproteinized bovine bone mineral (DBBM). Micro-CT and histological analyses consistently revealed a decreased newly regenerated bone volume for CKD rats after 4 and 8 weeks. In addition, 1.4-mm-diameter cortical bone defects were established in the distal end of femora and filled with gelatin sponge. CKD rats exhibited significantly lower values of regenerated bone and bone mineral density (BMD) within the cortical gap after 2 and 4 weeks. Moreover, histomorphometric analysis showed an increase in both osteoblast number (N.Ob/B.Pm) and osteoclast number (N.Oc/B.Pm) in CKD groups due to hyperparathyroidism. Notably, collagen maturation was delayed in CKD rats as verified by Masson’s Trichrome staining. These data indicate that declined renal function negatively affects bone regeneration in both calvarial and femoral defects.

Estrogen Deficiency Leads to Further Bone Loss in the Mandible of CKD Mice

Background

Chronic kidney disease (CKD) has been regarded as a grave public health problem. Estrogen is a critical factor for both renal protection and bone remodeling. Our previous study demonstrated that CKD impairs the healing of titanium implants. The aim of this study was to investigate the effects of estrogen deficiency on the mandibular bone in CKD mice.

Methods

Forty eleven-week-old female C57BL mice were used in this study. Uremia and estrogen deficiency were induced by 5/6 nephrectomy and ovariectomy (OVX), respectively. After 8 weeks, the mice were sacrificed, and their mandibles were collected for micro-CT analysis and histological examination.

Results

All the mice survived the experimental period. Serum measurements confirmed a significant increase in BUN in the CKD group that was further increased by OVX. OVX led to significant decreases in both the BV/TV and cortical thickness of the mandibular bone in CKD mice.

Conclusion

In summary, our findings indicate that estrogen deficiency leads to further mandibular bone loss in CKD mice.

Fracture Burden and Risk Factors in Childhood CKD: Results from the CKiD Cohort Study

Childhood chronic kidney disease (CHD) poses multiple threats to bone accrual; however, the associated fracture risk is not well characterized. This prospective cohort study included 537 CKD in Children (CKiD) participants. Fracture histories were obtained at baseline, at years 1, 3, and 5 through November 1, 2009, and annually thereafter. We used Cox regression analysis of first incident fracture to evaluate potential correlates of fracture risk. At enrollment, median age was 11 years, and 16% of patients reported a prior fracture. Over a median of 3.9 years, 43 males and 24 females sustained incident fractures, corresponding to 395 (95% confidence interval [95% CI], 293-533) and 323 (95% CI, 216-481) fractures per 10,000 person-years, respectively. These rates were 2- to 3-fold higher than published general population rates. The only gender difference in fracture risk was a 2.6-fold higher risk in males aged ≥15 years (570/10,000 person-years, adjusted P=0.04). In multivariable analysis, advanced pubertal stage, greater height Z-score, difficulty walking, and higher average log-transformed parathyroid hormone level were independently associated with greater fracture risk (all P≤0.04). Phosphate binder treatment (predominantly calcium-based) was associated with lower fracture risk (hazard ratio, 0.37; 95% CI, 0.15-0.91; P=0.03). Participation in more than one team sport was associated with higher risk (hazard ratio, 4.87; 95% CI, 2.21-10.75; P<0.001). In conclusion, children with CKD have a high burden of fracture. Regarding modifiable factors, higher average parathyroid hormone level was associated with greater risk of fracture, whereas phosphate binder use was protective in this cohort.

Mineral metabolism and cortical volumetric bone mineral density in childhood chronic kidney disease

CONTEXT

The relationships among cortical volumetric bone mineral density (CortBMD) and comprehensive measures of mineral metabolism have not been addressed in chronic kidney disease (CKD).

OBJECTIVE

The aim of the study was to identify the determinants of CortBMD in childhood CKD. A secondary objective was to assess whether CortBMD was associated with subsequent fracture.

DESIGN AND PARTICIPANTS

This prospective cohort study included 171 children, adolescents, and young adults (aged 5-21 years) with CKD stages 2-5D at enrollment and 89 1 year later.

OUTCOMES

Serum measures included vitamin D [25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25(OH)₂D), 24,25-dihydroxyvitamin D], vitamin D-binding protein, intact PTH, fibroblast growth factor 23, calcium, and phosphorus. Tibia quantitative computed tomography measures of CortBMD were expressed as sex-, race-, and age-specific Z-scores based on 675 controls. Multivariable linear regression identified the independent correlates of CortBMD Z-scores and the change in CortBMD Z-scores.

RESULTS

Lower calcium (β = .31/1 mg/dL, P = .01) and 25(OH)D (β = .18/10 ng/mL, P = .04) and higher PTH (β = -.02/10%, P = .002) and 1,25(OH)₂D (β = -.07/10%, P < .001) were independently associated with lower CortBMD Z-scores at baseline. The correlations of total, free, and bioavailable 25(OH)D with CortBMD did not differ. Higher baseline 1,25(OH)₂D (P < .05) and greater increases in PTH (P < .001) were associated with greater declines in CortBMD Z-scores. Greater increases in calcium concentrations were associated with greater increases in CortBMD Z-scores in growing children (interaction P = .009). The hazard ratio for fracture was 1.75 (95% confidence interval 1.15-2.67; P = .009) per SD lower baseline CortBMD.

CONCLUSIONS

Greater PTH and 1,25(OH)₂D and lower calcium concentrations were independently associated with baseline and progressive cortical deficits in childhood CKD. Lower CortBMD Z-score was associated with increased fracture risk.

Changes in bone structure and the muscle-bone unit in children with chronic kidney disease

The impact of pediatric chronic kidney disease (CKD) on acquisition of volumetric bone mineral density (BMD) and cortical dimensions is lacking. To address this issue, we obtained tibia quantitative computed tomography scans from 103 patients aged 5-21 years with CKD (26 on dialysis) at baseline and 12 months later. Gender, ethnicity, tibia length, and/or age-specific Z-scores were generated for trabecular and cortical BMD, cortical area, periosteal and endosteal circumference, and muscle area based on over 700 reference subjects. Muscle area, cortical area, and periosteal and endosteal Z-scores were significantly lower at baseline compared with the reference cohort. Cortical BMD, cortical area, and periosteal Z-scores all exhibited a significant further decrease over 12 months. Higher parathyroid hormone levels were associated with significantly greater increases in trabecular BMD and decreases in cortical BMD in the younger patients (significant interaction terms for trabecular BMD and cortical BMD). The estimated glomerular filtration rate was not associated with changes in BMD Z-scores independent of parathyroid hormone. Changes in muscle and cortical area were significantly and positively associated in control subjects but not in CKD patients. Thus, children and adolescents with CKD have progressive cortical bone deficits related to secondary hyperparathyroidism and potential impairment of the functional muscle-bone unit. Interventions are needed to enhance bone accrual in childhood-onset CKD.

Relationship between aortic mineral elements and osteodystrophy in mice with chronic kidney disease

In chronic kidney disease (CKD), osteodystrophy and arterial calcification often coexist. However, arterial alterations have not been addressed in CKD unaccompanied by evidence of calcification. We investigated the association of phosphate (P) and calcium (Ca) accumulation in calcification-free aortas with CKD-induced osteodystrophy. Aortic accumulation of magnesium (Mg), an inhibitor of calcification, was also examined. Male mice aged 26 weeks with CKD characterized by hyperparathyroidism and hyperphosphatemia (Nx, n = 8) and age-matched healthy male mice (shams, n = 8) were sampled for blood, and thoracic vertebrae and aortas were harvested. Bone structure and chemicals were analyzed by microcomputed tomography and infrared microspectroscopy, respectively, and aortic accumulation of P, Ca, and Mg was evaluated by plasma-atomic emission spectrometry. Volume fractions of cortical and trabecular bones were smaller in Nx than in sham animals (P < 0.05), attributed to cortical thinning and reduction in trabecular number, respectively. Bone chemicals were not different between the groups. No calcification was found in either group, but P, Ca, and Mg contents were higher in Nx than in shams (P < 0.05). The mass ratio of Ca/P was lower in Nx than in shams (P < 0.05), but that of Mg/Ca and Mg/P was not different between the groups. Aortic P and Ca contents were inversely correlated with the volume fraction of cortical bone (P < 0.05). In conclusion, the relationship of osteodystrophy with aortic P and Ca accumulation suggests the existence of a bone-vascular axis, even in calcification-free arteries in CKD. The preservation of ratios of Mg/Ca and Mg/P despite CKD development might contribute to calcification resistance.

Cinacalcet hydrochloride therapy for secondary hyperparathyroidism in hemodialysis patients

This study compared the efficacy of a cinacalcet-based regimen with unrestricted conventional therapy (vitamin D and phosphate binders) for achieving Kidney Disease Outcome Quality Initiative (K/DOQI) targets for dialysis patients. In this multicenter, prospective study, hemodialysis patients with poorly controlled secondary hyperparathyroidism (SHPT) were randomized to receive a cinacalcet-based regimen (n=55) or a conventional therapy (n=27). Doses of cinacalcet, vitamin D sterols, and phosphate binders were adjusted during a 12-week dose-titration phase to achieve intact parathyroid hormone (iPTH) levels ≤ 31.8 pmol/L. The primary end point was the percentage of patients with values in this range during a 24-week efficacy-assessment phase. The clinical response to 36-week cinacalcet treatment was evaluated. A dual energy X-ray absorptiometry was performed before and after 36 weeks of cinacalcet therapy. Fifty-eight percent of the cinacalcet group reached the primary end point, as compared with 19% of the conventional therapy group (P=0.001). A higher percentage of patients receiving the cinacalcet-based regimen versus conventional therapy achieved the targets for calcium, phosphorus and Ca×P. Achievement of targets was greatest in patients with less severe disease (intact PTH range, 31.8 to 53 pmol/L). Cinacalcet therapy increased proximal femur bone mineral density (BMD), but did not affect the lumbar spine. Itching intensity decreased significantly. Cinacalcet based treatment facilitates achievement of the K/DOQI targets for iPTH and bone mineral metabolism compared with conventional therapy in hemodialysis patients. Suppression of iPTH with cinacalcet reverses bone loss in the proximal femur. Cinacalcet alleviated itching.

Volumetric bone mineral density and bone structure in childhood chronic kidney disease

Chronic kidney disease (CKD) is associated with increased fracture risk and skeletal deformities. The impact of CKD on volumetric bone mineral density (vBMD) and cortical dimensions during growth is unknown. Tibia quantitative computed tomographic scans were obtained in 156 children with CKD [69 stages 2 to 3, 51 stages 4 to 5, and 36 stage 5D (dialysis)] and 831 healthy participants aged 5 to 21 years. Sex-, race-, and age- or tibia length-specific Z-scores were generated for trabecular BMD (TrabBMD), cortical BMD (CortBMD), cortical area (CortArea) and endosteal circumference (EndoC). Greater CKD severity was associated with a higher TrabBMD Z-score in younger participants (p < .001) compared with healthy children; this association was attenuated in older participants (interaction p < .001). Mean CortArea Z-score was lower (p < .01) in CKD 4-5 [-0.49, 95% confidence interval (CI) -0.80, -0.18)] and CKD 5D (-0.49, 95% CI -0.83, -0.15) compared with healthy children. Among CKD participants, parathyroid hormone (PTH) levels were positively associated with TrabBMD Z-score (p < .01), and this association was significantly attenuated in older participants (interaction p < .05). Higher levels of PTH and biomarkers of bone formation (bone-specific alkaline phosphatase) and resorption (serum C-terminal telopeptide of type 1 collagen) were associated with lower CortBMD and CortArea Z-scores and greater EndoC Z-score (r = 0.18-0.36, all p ≤ .02). CortBMD Z-score was significantly lower in CKD participants with PTH levels above versus below the upper limit of the Kidney Disease Outcome Quality Initiative (KDOQI) CKD stage-specific target range: -0.46 ± 1.29 versus 0.12 ± 1.14 (p < .01). In summary, childhood CKD and secondary hyperparathyroidism were associated with significant reductions in cortical area and CortBMD and greater TrabBMD in younger children. Future studies are needed to establish the fracture implications of these alterations and to determine if cortical and trabecular abnormalities are reversible.

A mandibular body fracture related to mouth-opening training in a dialysis patient

A mandibular body fracture related to mouth-opening training in a dialysis patient is reported. A 61-year-old male patient had noticed pain in the right mandibular body and difficulty in mouth opening a week previously. The patient had been performing mouth-opening training for a couple of weeks. The right lower face was slightly swollen with tenderness at the right lower border of the mandible. Hypoesthesia of the right lower lip was also observed. A bone step was palpable on the alveolar ridge of the right mandible, but mobility was not marked. The mandible was atrophic in the body region with only four anterior teeth left. Panoramic X-ray examination revealed a moderately displaced fracture in the right molar region of the mandible. The patient had no severe pain or difficulty in eating using a partial denture. The patient had received dialysis for 17 years and had also been treated by warfarin and aspirin. The patient was followed up under restricted mouth opening. Osteosynthesis with bone remodeling was confirmed after 6 months by X-ray examination. No complication requiring further treatment occurred during the follow-up period. In this patient, a medically compromised condition under long-term dialysis is considered a predisposing factor, which made the atrophic mandible more susceptible to the stress related to mouth-opening training.

Management of osteoporosis in CKD Stages 3 to 5

Osteoporosis and chronic kidney disease (CKD) are both common conditions of older adults and both may be associated with substantial morbidity. However, biochemical and histologic changes that occur with progressive kidney disease require specific interventions, some of which may be concordant with osteoporosis management in the general population, whereas others may be less relevant or perhaps even harmful. In this article, we review the diagnosis of and management strategies for osteoporosis in individuals with CKD, placing these into perspective with the recently published KDIGO (Kidney Disease: Improving Global Outcomes) guidelines for treatment of CKD-mineral and bone disorder (CKD-MBD). Specifically, we highlight osteoporosis treatment recommendations by CKD stage and discuss new avenues for osteoporosis treatment that may be useful in individuals with CKD.

Characterization of mandibular bone in a mouse model of chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a worldwide health problem with increasing prevalence and poor outcomes, including severe cardiovascular disease and renal osteodystrophy. With advances in medical treatment, patients with CKD are living longer and require oral care. The aim of this study is to determine the effects of CKD and dietary phosphate on mandibular bone structure using a uremic mouse model.

METHODS

Uremia (U) was induced in female dilute brown agouti/2 mice by partial renal ablation. Uremic mice received a normal-phosphate (NP) or a high-phosphate (HP) diet. sham surgeries were performed in a control group of mice; half received an NP diet, and the other half was fed an HP diet. At termination, animals were sacrificed, and mandibles were collected for microcomputed tomography (micro-CT) and histologic analysis.

RESULTS

Sera levels of blood urea nitrogen, parathyroid hormone, and alkaline phosphatase were significantly increased in U/NP and U/HP mice versus sham controls, whereas serum calcium was increased in the U/HP group, and no differences were noted in serum phosphate levels among groups. Micro-CT analyses revealed a significant reduction in cortical bone thickness and an increase in trabecular thickness and trabecular bone volume/tissue volume in U/NP and U/HP groups compared to the sham/NP group. A significant reduction in cortical bone thickness was also found in the sham/HP group versus the sham/NP group. Histologic evaluation confirmed increased trabeculation in the U groups.

CONCLUSION

CKD in mice, especially under conditions of HP feeding, results in marked effects on alveolar bone homeostasis.

Bone histomorphometry in renal osteodystrophy

On bone biopsies from patients with chronic kidney disease, measurements are made of the turnover, mineralization, and volume. Turnover depends on the bone formation rate and bone resorption rate; the former can be measured using tetracycline labelling. The osteoid width and bone apposition rate determine the mineralization rates. Bone volume includes both mineralized and unmineralized bone and is directly related to the porosity. Using these measurements, biopsies can be separated into the classic types of renal osteodystrophy: normal, adynamic, high-turnover, mixed, and osteomalacia. Fracture rates among these types are not consistent, but several studies have found high fracture rates with adynamic or osteomalacia. The bone density tests cannot distinguish between different types of bone histology.

Usefulness of bone uptake ratio of bone scintigraphy in hemodialysis patients

OBJECTIVE

It is important to estimate the bone metabolism in patients with renal osteodystrophy. The methods of estimation must be noninvasive, accurate, and able to measure repeatedly.

METHODS

The regions of interest on bone scintigraphy were drawn over the radius in 22 hemodialysis patients (10 males, 12 females). The bone/soft tissue ratio (B/ST ratio) was calculated for all patients. The bone soft tissue ratio of both skull (S) and radius (R) was obtained from the resultant count ratios. We investigated the correlation between intact parathyroid hormone (PTH), alkaline phosphatase (ALP) and the uptake ratios S and R.

RESULTS

Intact PTH had a significantly linear correlation with R (r = 0.745, p < 0.0001) and S (r = 0.702, p = 0.0001). ALP also had a significantly linear correlation with R (r = 0.537, p = 0.009) and S (r = 0.772, p < 0.0001).

CONCLUSION

The measurement of the bone soft tissue ratio of radius on bone scintigraphy was crucial for estimating renal osteodystrophy.

A structural approach to skeletal fragility in chronic kidney disease

Renal osteodystrophy is a multifactorial disorder of bone metabolism in chronic kidney disease (CKD). As CKD progresses, ensuing abnormalities in mineral metabolism result in distortions in trabecular microarchitecture, thinning of the cortical shell, and increased cortical porosity. Recent studies have shown significantly increased hip fracture rates in CKD stages 3 and 4, in dialysis patients, and in transplant recipients. The majority of studies of bone loss in CKD relied on dual-energy x-ray absorptiometry (DXA) measures of bone mineral density. However, DXA summarizes the total bone mass within the projected bone area, concealing distinct structural alterations in trabecular and cortical bone. Recent data have confirmed that peripheral quantitative computed tomography (pQCT) measures of cortical density and thickness provide substantially better fracture discrimination in dialysis patients, compared with hip or spine DXA. This review summarizes the growing evidence for bone fragility in CKD stages 3 through 5, considers the effects of CKD on trabecular and cortical bone structure as it relates to fracture risk, and details the potential advantages and disadvantages of DXA and alternative measures of bone density, geometry, and microarchitecture, including pQCT, high-resolution pQCT, and micro-magnetic resonance imaging for fracture risk assessment in CKD.

Proton pump inhibitor omeprazole use is associated with low bone mineral density in maintenance haemodialysis patients

OBJECTIVE

Limited studies have shown that proton pump inhibitor (PPI) therapy may decrease bone density or insoluble calcium reabsorption through induction of hypochlorhydria. However, PPI therapy may also reduce bone resorption via inhibition of osteoclastic vacuolar proton pumps. The aim of this study was to determine whether the opposing effects of PPI therapy may cause clinically important alterations in bone mineral densitometry (BMD) parameters in maintenance haemodialysis patients.

METHODS

Sixty-eight maintenance haemodialysis patients were enrolled in this study. Patients were classified into two groups involving users of PPI therapy (omeprazole 20 mg/day, group 1, n = 36 patients) and non-users of acid suppression drugs (group 2, n = 32 patients). Patients had radius, hip and spine BMD assessed by dual-energy X-ray absorptiometry.

RESULTS

The mean duration of PPI therapy with omeprazole was 27 +/- 5 months. The users of PPI therapy had lower values of bone mineral density and T-scores at the anatomical regions than non-users of acid suppression drugs. Serum calcium and phosphate levels, calcium-phosphate product and serum intact parathormone levels and the ratio of users of vitamin D therapy were similar among groups. A mutivariable adjusted odds ratio for lower bone density associated with more than 18 months of omeprazole, when all the potential confounders were considered, was 1.31 in the proximal radius, 0.982 in the femur neck, 0.939 in the trochanter and 1.192 in the lumbal spine.

CONCLUSION

The present data suggest that PPI therapy should be cautiously prescribed in maintenance haemodialysis patients, especially with lower BMD values.

Histomorphometric measurements of bone turnover, mineralization, and volume

A recent Kidney Disease: Improving Global Outcomes report suggested that bone biopsies in patients with chronic kidney disease should be characterized by determining bone turnover, mineralization, and volume. This article focuses on the calculations and interpretation of these measurements. In most cases of renal osteodystrophy, the bone formation rate is roughly similar to the bone resorption rate; therefore, the bone formation indices can be used to describe turnover. It is important to remember that these conventions will not apply in some situations. Activation frequency should not be confused with bone formation rate or bone metabolic unit birth rate. Abnormal mineralization can be described using the osteoid volume, increased osteoid maturation time, or increased mineralization lag time. The concept of bone volume is the easiest to understand, but there is a large error from one biopsy to the next in the same person. There are some difficulties with each of the measurements, and further research in patients with chronic kidney must be done to enable a consensus to be reached about cut points to define categories within the spectrum of renal osteodystrophy and how to evaluate treatment responses.

Chronic kidney disease and bone fracture: a growing concern

Susceptibility to fracture is increased across the spectrum of chronic kidney disease (CKD). Moreover, fracture in patients with end-stage kidney disease (ESKD) results in significant excess mortality. The incidence and prevalence of CKD and ESKD are predicted to increase markedly over the coming decades in conjunction with the aging of the population. Given the high prevalence of both osteoporosis and CKD in older adults, it is of the utmost public health relevance to be able to assess fracture risk in this population. Dual-energy X-ray absorptiometry (DXA), which provides an areal measurement of bone mineral density (aBMD), is the clinical standard to predict fracture in individuals with postmenopausal or age-related osteoporosis. Unfortunately, DXA does not discriminate fracture status in patients with ESKD. This may be, in part, because excess parathyroid hormone (PTH) secretion may accompany declining kidney function. Chronic exposure to high PTH levels preferentially causes cortical bone loss, which may be partially offset by periosteal expansion. DXA can neither reliably detect changes in bone volume nor distinguish between trabecular and cortical bone. In addition, DXA measurements may be low, normal, or high in each of the major forms of renal osteodystrophy (ROD). Moreover, postmenopausal or age-related osteoporosis may also affect patients with CKD and ESKD. Currently, transiliac crest bone biopsy is the gold standard to diagnose ROD and osteoporosis in patients with significant kidney dysfunction. However, bone biopsy is an invasive procedure that requires time-consuming analyses. Therefore, there is great interest in developing non-invasive high-resolution imaging techniques that can improve fracture risk prediction for patients with CKD. In this paper, we review studies of fracture risk in the setting of ESKD and CKD, the pathophysiology of increased fracture risk in patients with kidney dysfunction, the utility of various imaging modalities in predicting fracture across the spectrum of CKD, and studies evaluating the use of bisphosphonates in patients with CKD.

A structural approach to the assessment of fracture risk in children and adolescents with chronic kidney disease

Children with chronic kidney disease (CKD) have multiple risk factors for impaired accretion of trabecular and cortical bone. CKD during childhood poses an immediate fracture risk and compromises adult bone mass, resulting in significantly greater skeletal fragility throughout life. High-turnover disease initially results in thickened trabeculae, with greater bone volume. As disease progresses, resorption cavities dissect trabeculae, connectivity degrades, and bone volume decreases. Increased bone turnover also results in increased cortical porosity and decreased cortical thickness. Dual-energy X-ray absorptiometry (DXA)-based measures of bone mineral density (BMD) are derived from the total bone mass within the projected bone area (g/cm(2)), concealing distinct disease effects in trabecular and cortical bone. In contrast, peripheral quantitative computed tomography (pQCT) estimates volumetric BMD (vBMD, g/cm(3)), distinguishes between cortical and trabecular bone, and provides accurate estimates of cortical dimensions. Recent data have confirmed that pQCT measures of cortical vBMD and thickness provide substantially greater fracture discrimination in adult dialysis patients compared with hip or spine DXA. The following review considers the structural effects of renal osteodystrophy as it relates to fracture risk and the potential advantages and disadvantages of DXA and alternative measures of bone density, geometry, and microarchitecture, such as pQCT, micro-CT (microCT), and micro magnetic resonance imaging (microMRI) for fracture risk assessment.

Structural and functional assessment of trabecular and cortical bone by micro magnetic resonance imaging

Osteoporosis is a multifactorial disorder of bone mineral homeostasis affecting the elderly. It is a major public health issue with significant socioeconomic consequences. Recent findings suggest that bone loss-the key manifestation of the disease-is accompanied by architectural deterioration, both affecting the bone's mechanical competence and susceptibility to fracture. This article reviews the potential of quantitative micro MRI (mu-MRI), including a discussion of the technical requirements for image acquisition, processing, and analysis for assessing the architectural implications of osteoporosis and as a means to monitor the response to treatment. With current technology, the resolution achievable in clinically acceptable scan times and necessary signal-to-noise ratio (SNR) is comparable to trabecular thickness. This limited spatial resolution regime demands processing and analysis algorithms designed to operate under such limiting conditions. It is shown that three different classes of structural parameters can be distinguished, characterizing scale, topology, and orientation. There is considerable evidence that osteoporotic bone loss affects all three classes but that topological changes, resulting from conversion of trabecular plates to rods, with the latter's eventual disconnection, are particularly prominent. Clinical applications discussed can be divided into those dealing with assessment of osteoporotic fracture risk as opposed to the study of the effect of disease progression and regression in response to treatment. Current data suggest that noninvasive assessment of cortical and trabecular bone (TB) architecture by mu-MRI may provide new surrogate endpoints to assess the efficacy of intervention in osteoporosis treatment and prevention.

Quantitative Microcomputed Tomography Assessment of Intratrabecular, Intertrabecular, and Cortical Bone Architecture in a Rat Model of Severe Renal Osteodystrophy

OBJECTIVE

To determine the effects of renal osteodystrophy (ROD) on bone microarchitecture in growing rats.

METHODS

A total of 24 rats underwent 5/6 nephrectomy (NX) and were fed a high-phosphorus diet to induce ROD; another 6 underwent sham NX. In vitro microcomputed tomography images (GEMS, London, Ontario, Canada) were obtained in the femoral metaphysis and midshaft.

RESULTS

Trabecular and cortical bone volume/total volume (BV/TV) were significantly lower in NX specimens because of pores within the trabeculae and along the endosteal surface. Topological analysis using component labeling in 3-dimensions verified that trabecular pores connected to the marrow space. After the trabecular pores were filled using a morphological filter, trabecular thickness was significantly increased in NX. In contrast, cortical thickness was significantly decreased in NX compared with controls; however, after filling the endocortical pores, thickness did not differ.

CONCLUSIONS

The ROD resulted in decreased cortical and trabecular BV/TV, increased porosity, and increased trabecular thickness. Advanced image processing algorithms demonstrated the effects of cortical and trabecular porosity on BV/TV and structure in ROD.

Minimodeling Reduces the Rate of Cortical Bone Loss in Patients With Secondary Hyperparathyroidism

BACKGROUND

Secondary hyperparathyroidism often causes progressive cortical thinning because of increased bone resorption at the endocortical surface and increases cortical porosity because of increased resorption at the intracortical surface. Because bone formation by minimodeling has not yet been reported in cortical bone, we investigated the effects of cortical minimodeling on the decrease in rate of bone loss.

METHODS

Thirty-five patients with secondary hyperparathyroidism were enrolled. Remodeling and minimodeling parameters at the endocortical and periosteal surfaces, as well as at the intracortical surface, were measured. Relationships between remodeling parameters and minimodeling parameters at each surface were investigated by using linear regression analysis. Cortical bone specimens were classified into 3 groups according to cortical width and cortical porosity values. Relationships of minimodeling parameters at the endocortical surface with cortical width and at the intracortical surface with cortical porosity were investigated.

RESULTS

Some minimodeling parameters showed positive correlations with serum parathyroid hormone levels and remodeling parameters. Minimodeling bone volume at the endocortical surface was greater in the narrow-cortical-width group than wide-cortical-width group, possibly slowing the progression of cortical thinning. Minimodeling volume at the intracortical surface was greater in the high-porosity than low-porosity group, possibly slowing the progression of intracortical resorption space enlargement. Minimodeling of the periosteal surface was found in 1 specimen.

CONCLUSION

Results show enhanced cortical minimodeling in patients with secondary hyperparathyroidism, possibly representing the decrease in rate of cortical bone loss.

Bone mineral density in children with chronic renal failure

Bone mineral density (BMD) is important in children and adolescents because of its relationship to long-term skeletal health, and because, in adults with chronic renal failure (CRF), a relationship between low BMD and vascular calcification has been suggested. To investigate the relationship between BMD and manipulable factors that might affect it, i.e. plasma calcium, phosphate and parathyroid hormone (PTH), 64 patients with a median glomerular filtration rate (GFR) of 31 (range 7-60) ml min(-1) 1.73 m(-2) and median age of 10.0 (4.1-16.9) years were followed over 1.3 (0.7-1.7) years at an average of 5 (3-14) clinic visits. At one visit, BMD of the lumbar spine was measured by dual energy X-ray absorptiometry. The mean BMD Z-score was normal (=0.0). Overall mean calcium, phosphate and PTH levels were in their respective normal ranges. The majority of the patients (72%) were treated with calcium carbonate, mean dose 65 mg kg(-1) day(-1); prescription was positively related to serum calcium levels and calcium-phosphate product (P=0.012 and P<0.01 respectively). Almost all patients (98%) were treated with alfacalcidol, mean dose 12 ng kg(-1) day(-1); prescription was not related to investigated factors. Patients grew well; there was no change in height standard deviation score (DeltaHtSDS=0.0). Normal BMD Z-score for age and sex can be achieved in children with CRF managed with the aim of maintaining normal PTH levels by dietary phosphate restriction, calcium-based phosphate binders and small doses of alfacalcidol. Further investigation of the underlying bone by the use of biopsy and histomorphometry is required to determine actual bone health.

Definition, evaluation, and classification of renal osteodystrophy: a position statement from Kidney Disease: Improving Global Outcomes (KDIGO)

Disturbances in mineral and bone metabolism are prevalent in chronic kidney disease (CKD) and are an important cause of morbidity, decreased quality of life, and extraskeletal calcification that have been associated with increased cardiovascular mortality. These disturbances have traditionally been termed renal osteodystrophy and classified based on bone biopsy. Kidney Disease: Improving Global Outcomes (KDIGO) sponsored a Controversies Conference on Renal Osteodystrophy to (1) develop a clear, clinically relevant, and internationally acceptable definition and classification system, (2) develop a consensus for bone biopsy evaluation and classification, and (3) evaluate laboratory and imaging markers for the clinical assessment of patients with CKD. It is recommended that (1) the term renal osteodystrophy be used exclusively to define alterations in bone morphology associated with CKD, which can be further assessed by histomorphometry, and the results reported based on a unified classification system that includes parameters of turnover, mineralization, and volume, and (2) the term CKD-Mineral and Bone Disorder (CKD-MBD) be used to describe a broader clinical syndrome that develops as a systemic disorder of mineral and bone metabolism due to CKD, which is manifested by abnormalities in bone and mineral metabolism and/or extra-skeletal calcification. The international adoption of these recommendations will greatly enhance communication, facilitate clinical decision-making, and promote the evolution of evidence-based clinical practice guidelines worldwide.

Severe hyperparathyroidism with bone abnormalities and metastatic calcification in rats with adenine-induced uraemia

BACKGROUND

Marked parathyroid hyperplasia with bone diseases and vascular calcification are unsolved issues in dialysis patients. In this study, we made azotemic model rats by adenine feeding and analyzed the development and progression of the abnormalities.

METHODS

Renal failure was induced in 8-week-old male Wistar rats by feeding 0.75% adenine-containing diet for 6 weeks. Serum parameters, parathyroid hyperplasia, bone changes and metastatic calcification were examined at 2, 4 and 6 weeks.

RESULTS

Progressive increase of serum creatinine and inorganic phosphate, and decreased levels of serum calcium and 1,25(OH)2D3 were confirmed. Markedly enlarged parathyroid glands and extremely high PTH levels were observed in all adenine-fed rats compared with the control (PTH: 199.3+/-58.0 vs 10.5+/-3.0 pmol/l, P<0.01, respectively, at 6 weeks). In cortical bone of the femur, the morphometric parameters showed increased bone resorption with increased fibrosis, whereas in the trabecular bone, bone resorption decreased and bone volume increased with a larger amount of osteoid compared with the control. Metastatic calcification in aorta, coronary artery and other soft tissues were also found in adenine-fed rats.

CONCLUSIONS

Uraemic rats made by adenine diet developed severe abnormalities of calcium metabolism in a relatively short period and therefore they may serve as a useful model for the analysis of parathyroid hyperplasia and vascular calcification in chronic renal failure.

Assessment of therapeutic effect in patients with secondary hyperparathyroidism using bone scintigraphy

OBJECTIVE

The semi-quantitative method of bone scintigraphy [bone to soft tissue (B/ST) ratio] has been used in diagnosing and evaluating systemic metabolic bone diseases. The aim of this study is to evaluate of the therapeutic effect of secondary hyperparathyroidism (SHP).

METHODS

The subjects were ten hemodialysis patients with SHP. Seven patients underwent parathyroidectomy (PTX), and 22-Oxacalcitoriol (derivative of 1,25-dihydroxyvitamin D3) (OCT) was given to three patients. Bone scintigraphy and blood tests [intact parathyroid hormone (PTH), alkaline phosphatase (ALP), calcium (Ca), phosphorus (P), bone alkaline phosphatase (BALP), and deoxypridinoline (DPYD)] were performed before and after treatment. Regions of interest were drown around cranium, lumbar vertebrae, femoral neck and soft tissue of left medial thigh to calculate the B/ST ratio.

RESULT

The B/ST ratios of cranium, lumbar vertebrae, and femoral neck were reduced significantly after PTX (cranium, p = 0.0079, lumbar vertebrae, p = 0.0282, femoral neck, p = 0.0252). Intact PTH, ALP, Ca, P, BALP and DPYD levels were reduced significantly after PTX (intact PTH, p = 0.003, Ca, p = 0.0005, P, p = 0.0393, ALP, p = 0.0051, DPYD, p = 0.0232, BALP, p = 0.0324). After OCT administration, the B/ST ratio of each bony region showed tendency to diminish, although not significantly. Intact PTH levels were reduced significantly, although ALP, BALP, and DPYD levels were not. Ca and P levels were increased significantly because of the medicinal action of OCT.

CONCLUSION

The B/ST ratio of cranium may be non-invasive method and have potential in evaluating the therapeutic effect of SHP.

Usefulness of whole PTH assay in patients with renal osteodystrophy —Correlation with bone scintigraphy

OBJECTIVE

Intact parathyroid hormone (PTH) assay has recently been reported to be effective in evaluating both 1-84 PTH (whole PTH) and inactive 7-84 PTH. Inactive 7-84 PTH is considered to be increased in hemodialysis patients and to prevent the effects of 1-84 PTH, and intact PTH is considered to overestimate the PTH activity in these patients. As such, a whole PTH assay has recently been developed. The purpose of this study was to examine the usefulness of a whole PTH assay using the bone to soft tissue (B/ST) ratio on bone scintigraphy.

METHOD

Twenty-five hemodialysis patients were included in our study. In all patients, bone scintigraphy and a blood test [whole PTH, intact PTH, alkaline phosphatase (ALP), calcium (Ca), and phosphorus (P)] were performed. Regions of interest (ROIs) were drawn around the cranium, lumbar vertebrae, left femoral neck, and soft tissue of the medial left thigh to obtain the B/ST ratio.

RESULTS

The B/ST ratio of the cranium and left femoral neck correlated with whole PTH and intact PTH. In particular, the B/ST ratio of the cranium correlated most significantly with the value of whole PTH. Whole PTH levels correlated with intact PTH levels (r = 0.891, p < 0.0001).

CONCLUSION

Our data indicate that a whole PTH assay may be useful in evaluating PTH activity using the B/ST ratio. The B/ST ratio of the cranium may reflect the bone metabolism of hemodialysis patients.

Serum levels of C-terminal telopeptide of type I collagen: a useful new marker of cortical bone loss in hemodialysis patients

Renal osteodystrophy is a major complication in hemodialysis patients. Measurement of serum peptide derived from the degradation of bone collagen could potentially provide an indirect estimate of bone resorption. The present study estimated the significance of the C-terminal telopeptide of type I collagen (beta-CTx) as a serum bone resorption marker in male hemodialysis patients. The mean age and hemodialysis duration of the 160 patients were 59.7 years (26-86 years) and 67.2 months (17-142 months), respectively. Bone mineral density (BMD) in the distal third of the radius was measured using dual-energy X-ray absorptiometry twice with a 2-year interval. A blood sample was collected immediately before the hemodialysis session at the time of the second BMD measurement. Other serum bone markers determined were bone-specific alkaline phosphatase (BAP) and intact and N-terminal midfragment (N-Mid) osteocalcin (OC) as bone-formation markers and serum pyridinoline (PYD) and deoxypyridinoline (DPD) as bone resorption markers. Serum beta-CTx correlated significantly in a positive manner with serum PYD, DPD, BAP, intact OC, and N-Mid OC. Serum beta-CTx, as well as PYD, DPD, BAP, intact OC, and N-Mid OC, correlated significantly with BMD in the distal third of the radius at the second measurement and with the rate of BMD reduction during the preceding 2 years. The highest quartile of serum beta-CTx was positively associated with rapid bone loss, defined as a change in the value for BMD in the distal third of the radius falling within the upper tertile of patients, in 55% of cases, and each quartile progress in serum beta-CTx increased the odds ratio of rapid bone loss by a factor of 1.73. Since the Youden index was twice as accurate for beta-CTx, BAP and N-Mid OC as for intact PTH, these bone-remodeling markers may be better risk markers of cortical bone loss than intact PTH. Inclusion in the highest quartile of PTH (above 288 pg/ml) predicted rapid bone loss with a sensitivity of only 26%. This means that the upper limit for serum PTH level recommended by K/DOQI may be too high, since 74% of cases with rapid bone loss showed serum PTH levels of below 288 pg/ml. In conclusion, serum measurement of beta-CTx may provide a new commercially viable and relevant serum assay to reflect cortical bone resorption in hemodialysis patients.

Effects of cinacalcet on bone mineral density in patients with secondary hyperparathyroidism

BACKGROUND

Cinacalcet, a calcimimetic agent, is effective in treating both primary and secondary hyperparathyroidism. Because hyperparathyroidism induces mineralized bone loss, we investigated the effects of cinacalcet treatment on bone mineral density (BMD) in patients with secondary hyperparathyroidism due to chronic kidney disease.

METHODS

Ten patients who were receiving haemodialysis and four patients, who had stage 4 chronic kidney disease participated and completed the multicentre, randomized, double-blind, placebo-controlled trials evaluating the safety and efficacy of cinacalcet for treating secondary hyperparathyroidism. The efficacy of cinacalcet was assessed by plasma intact parathyroid hormone (iPTH) levels. A dual energy X-ray absorptiometry was performed to measure the BMD of total proximal femurs and lumbar spine (L2-L4) before and after 26 weeks of treatment.

RESULTS

Cinacalcet reduced iPTH from 912+/-296 to 515+/-359 pg/ml in haemodialysis patients and from 210+/-46 to 56+/-51 pg/ml in pre-dialysis patients (means+/-SD; both P<0.05). When data from haemodialysis and pre-dialysis patients were pooled for analysis, cinacalcet treatment increased proximal femur BMD from 0.945+/-0.169 to 0.961+/-0.174 g/cm(2) (P<0.05), but did not affect lumbar spine BMD. There was a correlation between the change in femur BMD and the change in iPTH during the study period (R(2) = 0.39, P<0.05).

CONCLUSIONS

Secondary hyperparathyroidism is associated with progressive bone loss. Suppression of plasma iPTH with cinacalcet appears to reverse bone loss in the proximal femur, but does not affect BMD of the lumbar spine. A larger study is warranted to confirm that cinacalcet has a beneficial effect on the skeletal system in patients with secondary hyperparathyroidism.

Posttransplantation Bone Disease

Transplanted patients experience rapid loss of bone, high fracture rates, and increases in morbidity and mortality as a consequence of a posttransplant scenario that is highly deleterious to the skeleton. Immune suppressive drugs, especially glucocorticoids, are toxic to bone, often acting on a background of preexisting osteodystrophy resulting from long-standing renal, hepatic, cardiac, or pulmonary disease. Cyclosporin and tacrolimus lead to a severe osteopenic state in rats, but the skeletal toxicity of the calcineurin inhibitors in the clinical environment is less clear. Nor is it clear whether cyclosporin and tacrolimus differ in their skeletal actions. Mycophenolate mofetil and sirolimus do not appear to have important skeletal toxicity. Preventative strategies include minimizing glucocorticoid exposure and implementing therapies to counter the increase in bone resorption and decrease in bone formation that follows transplantation. Antiresorptive agents, especially bisphosphonates, appear capable of retarding or halting the early bone loss and possibly reduce fracture rates also. Vitamin D and calcium are ineffective, but calcitriol has utility in some reports. Bone anabolic agents, such as synthetic parathyroid hormone and growth hormone, have potential, but data are lacking.

Risk factors for decreased total body and regional bone mineral density in hemodialysis patients with severe secondary hyperparathyroidism

Hyperparathyroidism contributes significantly to decreased bone mineral density (BMD) in end-stage renal disease patients, but this negative influence is not homogeneous throughout the skeleton. We studied the BMD by dual-energy X-ray absorptiometry on total body and on different regions of the skeleton in 42 patients with severe hyperparathyroidism on hemodialysis. We also evaluated the relationship between different risk factors and BMD found on the regions examined in these patients. The legs and other sites where cortical bone predominate were mostly affected, whereas trabecular bone was relatively preserved. This is probably the result of the different effects of hyperparathyroidism on cortical and trabecular bone, but we cannot rule out the interference of ectopic calcifications and sclerotic lesions of vertebral end-plates falsely increasing lumbar spine BMD. The main determinants of low total-body BMD were, in order of importance, immobility, high intact parathyroid hormone levels, low body mass index, and low albumin. Eleven patients presented with pathologic fractures, mainly in the legs, and BMD was lower in this group than in patients without fractures. In conclusion, our study makes clear that hyperparathyroidism is a great threat to bone density in hemodialysis patients, mainly in the legs, the site mostly affected by fragility fractures in our patients. Physicians must worry not only with high parathyroid hormone levels, but also with the nutritional state of these patients.

Quantitative high-resolution magnetic resonance imaging reveals structural implications of renal osteodystrophy on trabecular and cortical bone

PURPOSE

To explore the potential role of micro-magnetic resonance imaging (micro-MRI) for quantifying trabecular and cortical bone structural parameters in renal osteodystrophy (ROD), a multifactorial disorder of bone metabolism, traditionally evaluated by bone biopsy.

MATERIALS AND METHODS

Seventeen hemodialysis patients (average PTH level = 502 +/- 415 microg/liter) were compared with 17 age-, gender-, and body mass index (BMI)-matched control subjects. The average dialysis duration for the patients was 5.5 years (range = 0.96-18.2 years). Three-dimensional (3D) fast large-angle spin-echo (FLASE) MR images of the distal tibia (voxel size = 137 x 137 x 410 microm(3)) were processed to yield bone volume fraction (BV/TV). From a skeletonized representation of the trabecular bone network, the topology of each bone voxel was determined providing surface and curve voxel densities (SURF and CURV) and the topological erosion index (EI). Further, high-resolution two-dimensional (2D) spin-echo images were collected at the tibial midshaft for measurement of cortical bone cross-sectional area (CCA), relative CCA expressed as a percentage of total bone area (RCA), and mean cortical thickness (MCT).

RESULTS

The data show both RCA and MCT to be lower in the patients (61.2 vs. 69.1%, P = 0.008, and 4.53 vs. 5.19 mm, P = 0.01). BV/TV and SURF were lower, while EI was increased in the patients, although these differences were not quite significant (P = 0.06-0.09). All of the cortical and trabecular findings are consistent with increased bone fragility.

CONCLUSION

The data suggest that micro-MRI may have potential to characterize the structural implications of metabolic bone disease, potentially providing a noninvasive tool for the evaluation of therapies for ROD.