Bone imaging and fracture risk assessment in kidney disease

Risk factors and renal outcomes of low bone mineral density in patients with non-dialysis chronic kidney disease

Bone disorder is a common complication of chronic kidney disease (CKD). The clinical usefulness of bone mineral density (BMD) in CKD is not well known. Our study shows that low BMD is associated with physical activity and dietary Na/K intake ratio and can predict poor renal outcome in non-dialysis CKD.

PURPOSE

Despite evidence of a link between bone mineral disorders and chronic kidney disease (CKD), the clinical implications of bone mineral density (BMD) in CKD are not well established. We investigated risk factors and renal outcomes of low BMD in CKD.

METHODS

We analyzed data from the KNOW-CKD. BMD measured by dual-energy x-ray absorptiometry was classified by T score: normal (T score ≥ - 1.0), osteopenia (- 1.0 > T score > - 2.5), and osteoporosis (T score ≤ - 2.5) of the lumbar spine, hip, or femoral neck. Logistic regression analysis to assess risk factors of low BMD (T score < - 1.0) and Cox proportional hazards models to estimate risk of incident end-stage renal disease (ESRD).

RESULTS

Low BMD was prevalent (osteopenia 33%; osteoporosis 8%) in 2128 adults with CKD (age 54 ± 12 years; male 61%). Over a median follow-up of 4.3 years, there were 521 cases of incident ESRD. Lower BMD was associated with female sex, older age, low eGFR, low BMI, and lifestyle factors of physical activity (odds ratio (OR) = 0.62, 95% confidence interval (0.49-0.77)) and spot urine Na/K ratio (1.07 (1.00-1.15)). In adjusted Cox models, low BMD was associated with increased incident ESRD (hazard ratio (HR) = 1.14 (0.92-1.41) for osteopenia; 1.43 (1.01-2.04) for osteoporosis, P for trend < 0.05) compared with the reference of normal BMD. The association between low BMD and ESRD was similar according to T score discordance classification.

CONCLUSIONS

Low BMD was associated with modifiable lifestyle factors including low physical activity and high dietary Na/K intake ratio. The presence of low BMD is associated with poor renal outcomes in non-dialysis CKD.

Trabecular bone score in patients with chronic kidney disease

Patients with chronic kidney disease have high risk of osteoporotic fractures. Lower trabecular bone score (TBS) was associated with poorer kidney function and higher fracture risk when kidney function was normal. Addition of TBS to The Fracture Risk Assessment Tool with bone mineral density did not improve fracture risk prediction.

INTRODUCTION

We sought to determine whether trabecular bone score (TBS) either independently or adjusted for The Fracture Risk Assessment Tool (FRAX) could predict risk of major osteoporotic fractures (MOFs) in a large population-based sample of patients with all stages of chronic kidney disease (CKD).

METHODS

We used population-based administrative databases to identify patients above age 20 years who had dual-energy X-ray absorptiometry (DXA) scan and serum creatinine measured within 1 year, during the years 2005 to 2010. Patients were excluded if they were on dialysis or had a functioning renal transplant. We stratified patients by estimated glomerular filtration rate (eGFR). We collected femoral neck bone mineral density (BMD), lumbar spine TBS, incident major osteoporotic fractures (MOF) and hip fractures, and other clinical characteristics.

RESULTS

Among 8289 patients, there were 6224 (75.1%) with eGFR ≥ 60 mL/min/1.73 m², 1624 (19.6%) with eGFR 30-60 mL/min/1.73 m², and 441 (5.3%) with eGFR < 30 mL/min/1.73 m². There were 593 patients (7.2%) with MOFs and 163 (2.0%) with hip fractures. Lower TBS score was associated with increased risk of MOF and hip fractures across all eGFR strata in unadjusted Cox proportional hazards models but after adjusting for FRAX with BMD, lower TBS was only statistically significant for MOF prediction for eGFR ≥ 60 mL/min/1.73 m².

CONCLUSION

Lower TBS scores were associated with lower eGFR and increased fracture risk in patients with eGFR ≥ 60 mL/min/1.73 m². However, the addition of TBS to the FRAX score with BMD did not significantly improve fracture risk prediction in patients with CKD.

Time course of rapid bone loss and cortical porosity formation observed by longitudinal μCT in a rat model of CKD

BACKGROUND

Rodent studies of bone in chronic kidney disease have primarily relied on end-point examinations of bone microarchitecture. This study used longitudinal in vivo microcomputed tomography (in vivo μCT) to characterize the onset and progression of bone loss, specifically cortical porosity, in the Cy/+ rat of model of CKD.

METHODS

Male CKD rats and normal littermates were studied. In vivo μCT scans of the right distal tibia repeated at 25, 30, and 35 weeks were analyzed for longitudinal changes in cortical and trabecular bone morphometry. In vitro μCT scans of the tibia and femur identified spatial patterns of bone loss across distal, midshaft and proximal sites.

RESULTS

CKD animals had reduced BV/TV and cortical BV at all time points but developed cortical porosity and thinning between 30 and 35 weeks. Cortical pore formation was localized near the endosteal surface. The severity of bone loss was variable across bone sites, but the distal tibia was representative of both cortical and trabecular changes.

CONCLUSIONS

The distal tibia was found to be a sensitive suitable site for longitudinal imaging of both cortical and trabecular bone changes in the CKD rat. CKD trabecular bone loss progressed through ~30 weeks followed by a sudden acceleration in cortical bone catabolism. These changes varied in timing and severity across individuals, and cortical bone loss and porosity progressed rapidly once initiated. The inclusion of longitudinal μCT in future studies will be important for both reducing the number of required animals and to track individual responses to treatment.

Factors Associated With Osteoporosis Care of Men Hospitalized for Hip Fracture: A Retrospective Cohort Study

Rates of postfracture DXA and pharmacotherapy appear to be declining despite their known benefits in fracture reduction. We sought to identify factors associated with osteoporosis care among male veterans aged 50 years and older after hip fracture and to evaluate trends in rates of care with an observational cohort design using US Department of Veterans Affairs’ (VA) inpatient, pharmacy, and outpatient encounters and Centers for Medicare and Medicaid Services outpatient pharmacy claims (2007 to 2014) from men aged 50 years and older treated for hip fracture (N = 7317). We used the Cox proportional hazards model with random effects for the admitting facility. A sensitivity analysis was performed for a subset of patients aged 65 to 99 dually enrolled in Medicare ( N = 5821). Overall, approximately 13% of patients had evidence of osteoporosis care within one year of fracture. In the adjusted model, rural residence was associated with lower likelihood of care, and several comorbidities were associated with higher likelihood of receiving care. In sensitivity analyses of patients dually enrolled in Medicare, rural residence remained associated with lower likelihood of osteoporosis care. Overall rates of care decreased over time, but rates of DXA in the VA remained stable. These findings highlight the ongoing problem of low rates of postfracture care among a population with the highest risk of future fracture and its associated morbidity and mortality. The rural disparity in care and differences in rates of care across healthcare delivery systems illustrates the importance of healthcare delivery systems in promoting pharmacotherapy and DXA after sentinel events. Because the VA removes a majority of cost barriers to care, this integrated healthcare system may outperform the private sector in access to care. However, declining rates of pharmacotherapy imply knowledge gaps that undermine quality care. © 2019 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Updates in CKD-Associated Osteoporosis

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is associated with bone loss and fractures. The purpose of this review is to provide clinicians with an overview of the underlying pathogenesis of CKD-associated osteoporosis, and a summary of the current diagnostic and therapeutic approaches to this disease.

RECENT FINDINGS

In 2017, the Kidney Disease Improving Global Outcomes Committee on Bone Quality updated their guidelines to include screening for osteoporosis and fracture risk by dual energy X-ray absorptiometry in patients with CKD. Once a diagnosis of osteoporosis and/or fracture risk is established, it is not clear how nephrologists should manage their patients. Patients with CKD should be screened for CKD-associated osteoporosis and considered for strategies that prevent bone loss and fractures. Assessment of bone turnover via imaging, biochemical testing, or bone biopsy can help guide the choice of therapy. Randomized controlled trials are needed to assess safety and efficacy of treatments to prevent bone loss and fractures.

Rethinking Bone Disease in Kidney Disease

Renal osteodystrophy (ROD) is the bone component of chronic kidney disease mineral and bone disorder (CKD-MBD). ROD affects bone quality and strength through the numerous hormonal and metabolic disturbances that occur in patients with kidney disease. Collectively these disorders in bone quality increase fracture risk in CKD patients compared with the general population. Fractures are a serious complication of kidney disease and are associated with higher morbidity and mortality compared with the general population. Furthermore, at a population level, fractures are at historically high levels in patients with end-stage kidney disease (ESKD), whereas in contrast the general population has experienced a steady decline in fracture incidence rates. Based on these findings, it is clear that a paradigm shift is needed in our approach to diagnosing and managing ROD. In clinical practice, our ability to diagnose ROD and initiate antifracture treatments is impeded by the lack of accurate noninvasive methods that identify ROD type. The past decade has seen advances in the noninvasive measurement of bone quality and strength that have been studied in kidney disease patients. Below we review the current literature pertaining to the epidemiology, pathology, diagnosis, and management of ROD. We aim to highlight the pressing need for a greater awareness of this condition and the need for the implementation of strategies that prevent fractures in kidney disease patients. Research is needed for more accurate noninvasive assessment of ROD type, clinical studies of existing osteoporosis therapies in patients across the spectrum of kidney disease, and the development of CKD-specific treatments. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Biopsy vs. peripheral computed tomography to assess bone disease in CKD patients on dialysis: differences and similarities

Results from bone biopsy and high-resolution peripheral quantitative computed tomography (HR-pQCT) were compared in 31 CKD patients. There was an agreement mainly for cortical compartment that may represent a perspective on the fracture risk assessment. HR-pQCT also provided some clues on the turnover status, which warrants further studies.

INTRODUCTION

Chronic kidney disease (CKD) patients are at high risk of bone disease. Although bone biopsy is considered the best method to evaluate bone disease, it is expensive and not always available. Here we have compared, for the first time, data obtained from bone biopsy and HR-pQCT in a sample of CKD patients on dialysis.

METHODS

HR-pQCT and dual-energy X-ray absorptiometry (DXA) were performed in 31 CKD patients (30 on dialysis). Biopsies were analyzed by quantitative histomorphometry, and classified according to TMV.

RESULTS

We have found an inverse correlation between radius cortical density measured by HR-pQCT, with serum, as well as histomorphometric bone remodeling markers. Trabecular density and BV/TV measured through HR-pQCT in the distal radius correlated with trabecular and mineralized trabecular bone volume. Trabecular number, separation, and thickness obtained from HR-pQCT and from bone biopsy correlated with each other. Patients with cortical porosity on bone histomorphometry presented lower cortical density at the distal radius. Cortical density at radius was higher while bone alkaline phosphatase was lower in patients with low turnover. Combined, these parameters could identify the turnover status better than individually.

CONCLUSIONS

There was an agreement between HR-pQCT and bone biopsy parameters, particularly in cortical compartment, which may point to a new perspective on the fracture risk assessment for CKD patients. Besides classical bone resorption markers, HR-pQCT provided some clues on the turnover status by measurements of cortical density at radius, although the significance of this finding warrants further studies.

Osteoprotegerin and uremic osteoporosis in chronic hemodialysis patients

INTRODUCTION

Osteoprotegerin (OPG) is a powerful inhibitor of osteoclast activity, and it plays an important role in bone metabolism. In hemodialysis (HD) patients, the relationship between OPG and bone mineral density (BMD) is important, but remains unclear yet. The study objective was to assess the OPG role related to uremic osteoporosis in HD patients.

METHODS

This cross-sectional study has been realized on a cohort of 63 chronic HD patients.

INCLUSION CRITERIA

elderly prevalent HD patients with an age over 55 years old.

EXCLUSION CRITERIA

previous bone disease or previous renal transplant; neoplasia; parathyroidectomy, hormone replacement therapy. The data regarding demographical and clinical characteristics, including treatments for mineral and cardiovascular complications, were recorded. Serum OPG and mineral markers levels were measured. BMD was assessed by calcaneus quantitative ultrasound; it measured broadband ultrasound attenuation, speed of sound (SOS) and stiffness index (STI).

RESULTS

The high OPG levels were associated with higher bone mineral density (OPG-SOS P = 0.003; R = 0.37; OPG-STI P = 0.03; R = 0.28). Malnutrition, anemia and advanced age correlated with bone demineralization. Males had higher bone density parameters than females. In patients treated with vitamin D (P = 0.005), the BMD was increased comparing to patients without these treatments.

CONCLUSIONS

OPG levels had directly correlated with bone mineral density parameters. Our study further confirms the critical role of OPG in the pathogenesis of uremic osteoporosis in ESRD. Whether the increased circulant OPG protect against bone loss in patients undergoing HD remains to be established.