The use of bone mineral density measured by dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed microtomography in chronic kidney disease

Obesity and Bone Mineral Density Protection Paradox in Chronic Kidney Disease: Secreted Protein Acidic and Rich in Cysteine as a Piece of the Puzzle?

Obesity is a health condition that represents a risk factor for numerous diseases and complications. However, obesity might also have-to some extent-some "benefits" in certain situations. This includes potential bone protection in patients suffering from chronic kidney disease. In an attempt to explain such a paradox, we highlight secreted protein acidic and rich in cysteine (SPARC) as a hypothetical mediator of this protection. Indeed, SPARC properties provide a logical rationale to describe such bone protection via its overexpression combined with its calcium-binding and collagen-binding properties. We believe that exploring such hypotheses could open new doors to elucidate unknown pathways towards developing a new generation of molecular therapies.

Bone and Chronic Kidney Disease

Chronic kidney disease (CKD) induces mineral and bone disorders (CKD-MBD) that affect calcium and phosphate metabolism. This review links pathophysiology, histologic aspects, and radiologic signs. CKD leads to bone lesions, namely renal osteodystrophy, which may combine low or high bone remodeling, impaired mineralization, and bone loss. CKD-MBD also comprises vascular calcifications, which, together with bone disease, lead to a high risk of cardiovascular events and osteoporotic fractures that increase both morbidity and mortality. Osteoporosis assessment is based on screening for classic risk factors and CKD-related factors (disease duration/severity, transplantation history, dialysis vintage). Treatment of mineral disorders may combine serum phosphate lowering drugs, natural vitamin D or its 1-α derivatives, or calcium-sensing receptor agonists. Treatment of osteoporosis is conventional in mild to moderate stages but more complex in severe CKD because evidence about the efficacy and safety of anti-osteoporosis drugs is scant.

Bone mass measurement by DXA should be interpreted with caution in the CKD population with vascular calcification

Background

KDIGO guidelines suggest the use of dual-energy X-ray absorptiometry (DXA) to assess bone mineral density (BMD) in patients with CKD 3a-5D. Previous studies have demonstrated an association between trabecular bone mass loss and coronary artery calcification (CAC) progression. This study aimed to prospectively investigate the relationship between BMD changes, quantified by DXA, and CAC progression in the non-dialyzed CKD population.

Methods

In this post hoc study, BMD by DXA was measured at the lumbar spine and total hip at baseline and 12-months. Patients were categorized according to BMD changes into 3 different groups: LOSS, UNCHANGED and GAIN. CAC quantification was obtained by multislice computed tomography at baseline and 12-months.

Results

87 patients (55.6 ± 10.7 years, 62% males, 30% diabetic, eGFR = 39.2 ± 18.1 mL/min/1.73m²) were enrolled. CAC was found in 41 (47%) of the patients at baseline and CAC progression in 25 (64%) of them. Considering the lumbar spine and total hip BMD changes together, 24%, 48%, and 25% of the patients were in the LOSS, UNCHANGED and GAIN groups, respectively. Compared to the UNCHANGED or LOSS groups, the GAIN group had an increase in calcium score (p = 0.04) and a higher proportion of patients with CAC progression (p = 0.01). In the logistic regression analysis, CAC progression was 4.5 times more likely to be in the GAIN group.

Conclusions

The association between the increase in BMD values and the progression of vascular calcification was the result of two concomitant processes overlapping, leading to a misinterpretation of DXA results. Thus, the use of DXA for the evaluation of bone mass, especially at the lumbar spine, must be applied with restraint and its results very carefully interpreted in CKD patients.

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DXA should be interpreted with caution in the CKD population.

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Vascular calcification progression is highly prevalent among CKD patients.

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The increase of BMD values by DXA should be taken with restraint in CKD patients particularly in those with vascular calcification progression.

Bone Biopsy for Histomorphometry in Chronic Kidney Disease (CKD): State-of-the-Art and New Perspectives

The use of bone biopsy for histomorphometric analysis is a quantitative histological examination aimed at obtaining quantitative information on bone remodeling, structure and microarchitecture. The labeling with tetracycline before the procedure also allows for a dynamic analysis of the osteoblastic activity and mineralization process. In the nephrological setting, bone biopsy is indicated to confirm the diagnosis of subclinical or focal osteomalacia and to characterize the different forms of renal osteodystrophy (ROD). Even if bone biopsy is the gold standard for the diagnosis and specific classification of ROD, the use of this approach is very limited. The main reasons for this are the lack of widespread expertise in performing or interpreting bone biopsy results and the cost, invasiveness and potential pain associated with the procedure. In this regard, the sedation, in addition to local anesthesia routinely applied in Italian protocol, significantly reduces pain and ameliorates the pain perception of patients. Concerning the lack of widespread expertise, in Italy a Hub/Spokes model is proposed to standardize the analyses, optimizing the approach to CKD patients and reducing the costs of the procedure. In addition, new tools offer the possibility to evaluate the osteogenic potential or the ability to form bone under normal and pathological conditions, analyzing mesenchymal stem cells and their ability to differentiate in the osteogenic lineage. In the same way, circulating microRNAs are suggested as a tool for exploring osteogenic potential. The combination of different diagnostic approaches and the optimization of the bioptic procedure represent a concrete solution to spread the use of bone biopsy and optimize CKD patient management.

The renal patient seen by non-renal physicians: the kidney embedded in the 'milieu intérieur'

Chronic kidney disease is defined as a decrease in renal function or evidence of kidney injury for >3 months. This represents an oversimplification that may confuse physicians. Thus kidney function is equated to glomerular filtration rate, which represents one of multiple kidney functions. Some potentially more important renal functions are lost earlier, such as the production for the anti-ageing factor Klotho. Overall, these changes modify the emergent properties of the body, altering the relationships between different organs and systems, in a manner that is difficult to predict the response to interventions based on normal physiology concepts, as there is a novel steady state of interorgan relations. In this regard we now discuss the impact of CKD on heart failure; osteomuscular and joint pain and bone fragility and fractures; and osteosarcopaenia as seen by a cardiologist, a rheumatologist and a geriatrician.

A Contemporary View of the Diagnosis of Osteoporosis in Patients With Axial Spondyloarthritis

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that primarily affects the axial joints. Altered bone metabolism associated with chronic inflammation leads to both new bone formation in the spine and increased bone loss. It is known that patients with axSpA have a high prevalence of osteoporosis and fractures. However, there is no consensus on which imaging modality is the most appropriate for diagnosing osteoporosis in axSpA. Bone mineral density measurement using dual-energy X-ray absorptiometry is the primary diagnostic method for osteoporosis, but it has notable limitations in patients with axSpA. This method may lead to the overestimation of bone density in patients with axSpA because they often exhibit abnormal calcification of spinal ligaments or syndesmophytes. Therefore, the method may not provide adequate information about bone microarchitecture. These limitations result in the underdiagnosis of osteoporosis. Recently, new imaging techniques, such as high-resolution peripheral quantitative computed tomography, and trabecular bone score have been introduced for the evaluation of osteoporosis risk in patients with axSpA. In this review, we summarize the current knowledge regarding imaging techniques for diagnosing osteoporosis in patients with axSpA.

Iliac crest bone biopsy by interventional radiologists to improve access to bone biopsy in chronic kidney disease populations: technical note and a case series

INTRODUCTION

Chronic kidney disease-mineral and bone disorder (CKD-MBD) leads to increased fracture risk. Iliac crest biopsy remains the gold standard for diagnosing bone disease in CKD. Unfortunately, bone biopsy is rarely performed which is mainly due to the inability of clinicians to perform the procedure. In this paper, we propose a fluoroscopy-guided procedure performed by interventional radiologists as a novel approach to iliac crest biopsy in adult population. We describe the implementation of the procedure and present the first 11 cases of CKD patients who underwent iliac crest biopsy with this new approach.

METHODS

A nephrologist already trained in performing iliac crest biopsy initiated the creation of a fluoroscopy-based iliac crest biopsy program. Two interventional radiologists underwent a short training. Patients' demographical, clinical and biochemical data were collected on the day of the biopsy. Complications within the first three months after the procedure were collected from electronical records.

RESULTS

IR rapidly mastered the procedure. The use of fluoroscopy allowed a precise localisation of the biopsy site and standardization of the intervention, which ensured specimen quality. The new approach allowed CKD patients to access iliac crest biopsy, which resulted in precise bone disease diagnosis (levels of bone turnover and mineralization) and targeted therapy for each case. There were no complications during, nor within 3 months after the intervention.

CONCLUSIONS

We believe this approach will increase the access to iliac crest biopsy for diagnosing bone disease in CKD population. Studies are now needed to evaluate whether CKD patients will benefit from anti-osteoporotic therapy based on the results of iliac crest biopsy.

Cortical unlike trabecular bone loss is not associated with vascular calcification progression in CKD patients

Background

Vascular calcification progression has been associated with the loss of trabecular bone in chronic kidney disease (CKD) patients. There are few data evaluating the relationship between cortical bone loss and vascular calcification in this population. The aim of this study was to prospectively evaluate the association between changes in cortical bone density and coronary artery calcification (CAC) progression in non-dialyzed CKD patients.

Methods

Changes of cortical and trabecular bone, and changes of calcium score, were analyzed using vertebral tomographic images from a prospective study. Automatic delineation of the cortical bone layer was performed by Image J software, and trabecular bone was determined by selecting a region of interest using Vitrea 2® software. Cortical and trabecular bone density (BD) were expressed in Hounsfield Units (HU), and coronary artery calcium score in Agatston Units (AU).

Results

Seventy asymptomatic patients [57.8 ± 10.2 years, 63% males, 20% diabetic, estimated glomerular filtration rate (eGFR) = 37.3 (24.8–51.3) mL/min/1.73m²] were followed for 24 months. The mean cortical and trabecular BD did not change over time. While 49 patients lost either bone, 29 (41%) patients lost cortical [− 4.4%/year (ranging from − 7.15 to − 0.5)] and 39 (56%) lost trabecular bone [− 3.15%/year (− 13.7 to − 0.25)]. There was no association between cortical and trabecular BD changes (p = 0.12). CAC was observed in 33 (46%) patients at baseline, and 30 (91%) of them showed CAC progression. While an inverse correlation between trabecular bone and calcium score changes was observed (p = 0.001), there was no correlation between cortical bone and calcium score changes (p = 0.34).

Conclusion

CKD patients experience either cortical or trabecular bone loss over time, but these changes do not take place simultaneously in all patients. Cortical, unlike trabecular bone loss, is not associated with vascular calcification progression in these patients.

Aortic pulse wave velocity is greater in peritoneal dialysis patients with lower dual energy X-ray absorptiometry (DXA) femoral neck bone mineral density

BACKGROUND

Increased vascular stiffness is associated with low bone mineral density (BMD) in the general population, and both are risk factors for mortality. We wished to determine whether vascular stiffness is associated with BMD in peritoneal dialysis (PD) patients.

METHODS

We measured vascular stiffness by aortic pulse wave velocity (aPWV), BMD by dual electron absorptiometry (DXA) scanning, and body composition using bioimpedance.

RESULTS

We reviewed DXA scans in 125 PD patients, 56.8% male, mean age 64.4 ± 15.3 years, mean aPWV, 10.2 ± 2.6 m/s. We divided patients by aPWV (< 10 and > 10 m/s), and there were no statistical differences in patient demographics, body composition, PD adequacy, peritoneal and urinary calcium losses. On univariate analysis aPWV was negatively associated with total body T score (r = - 0.20, p = 0.037). On multivariable logistic regression patients with higher aPWV were prescribed fewer non-calcium containing phosphate binders, odds ratio (OR) 0.83, 95% confidence interval (CI) 0.70-0.99, p = 0.039, more had lower 25 hydroxy-vitamin D₃ concentrations < 50 ng/L (OR 0.34, CI 0.12-0.93, p = 0.035, and lower femoral BMD OR 0.03 (CI 0-0.3.4), p = 0.029, but there was no association with total or lumbar spine BMD.

CONCLUSION

Our study reinforces the hypothesis of a link between bone disease and vascular disease in dialysis patients. As patients with higher aPWV were prescribed fewer non-calcium containing phosphate binders and fewer had higher 25 hydroxy-vitamin D₃ concentrations, then this raises the possibility that differences in clinical practice and drug prescribing may help to reduce vascular stiffness, which will require testing in future trials.