Update on renal osteodystrophy: pathogenesis and clinical management

Management of osteoporosis in patients with chronic kidney disease

Patients with CKD have a 4-fivefold higher rate of fractures. The incidence of fractures increases with deterioration of kidney function. The process of skeletal changes in CKD patients is characterized by compromised bone strength because of deterioration of bone quantity and/or quality. The fractures lead to a deleterious effect on the quality of life and higher mortality in patients with CKD. The pathogenesis of bone loss and fracture is complex and multi-factorial. Renal osteodystrophy, uremic milieu, drugs, and systemic diseases that lead to renal failure all contribute to bone damage in CKD patients. There is no consensus on the optimal diagnostic method of compromised bone assessment in patients with CKD. Bone quantity and mass can be assessed by dual-energy x-ray absorptiometry (DXA) or quantitative computed tomography (QCT). Bone quality on the other side can be assessed by non-invasive methods such as trabecular bone score (TBS), high-resolution bone imaging methods, and invasive bone biopsy. Bone turnover markers can reflect bone remodeling, but some of them are retained by kidneys. Understanding the mechanism of bone loss is pivotal in preventing fracture in patients with CKD. Several non-pharmacological and therapeutic interventions have been reported to improve bone health. Controlling laboratory abnormalities of CKD-MBD is crucial. Anti-resorptive therapies are effective in improving BMD and reducing fracture risk, but there are uncertainties about safety and efficacy especially in advanced CKD patients. Accepting the prevalent of low bone turnover in patients with advanced CKD, the osteo-anabolics are possibly promising. Parathyroidectomy should be considered a last resort for intractable cases of renal hyperparathyroidism. There is a wide unacceptable gap in osteoporosis management in patients with CKD. This article is focusing on the updated management of CKD-MBD and osteoporosis in CKD patients. Chronic kidney disease deteriorates bone quality and quantity. The mechanism of bone loss mainly determines pharmacological treatment. DXA and QCT provide information about bone quantity, but assessing bone quality, by TBS, high-resolution bone imaging, invasive bone biopsy, and bone turnover markers, can guide us about the mechanism of bone loss.

The Impact of Hemodialysis on Spatio-Temporal Characteristics of Gait and Role of Exercise: A Systematic Review

Background: People with end-stage kidney disease (ESKD) on hemodialysis (HD) commonly have functional impairments. The purpose of this systematic review was to evaluate the effect of HD on spatio-temporal characteristics of gait, and effect of exercise on these parameters. Methods: Electronic databases were searched to identify relevant citations. Extracted data was computed using a random effects model for means (Hedges’ and 95% confidence interval (CI). Results: 27 studies met inclusion criteria. Mean values: gait speed (GS)—1.0 m/s (CI: 0.9–1.1 m/s; 16 studies), fast walking speed (FWS)—1.5 m/s (CI: 1.3–1.6 m/s; 7 studies), timed get-up & go test (TUG) —6.8 s (CI: 6.1–7.5 s; 2 studies), walk tests (WT) 193.0 s (CI: 116.0–270.0; 5 studies), 6 min-walk-test (6MWT)—386.6 m (CI: 243.2–530.0 m; 11 studies). 4 studies compared participants on HD with normal controls and 10 studies evaluated the effect of nutrition/exercise. Conclusions: Compared to age-matched populations, people with ESKD/HD had significantly slower GS and reduced walk distances; with intervention, the change in the distance walked was significant. Further research is required to evaluate the effect of HD on gait parameters, and the type of exercise/nutrition that will lead to meaningful changes.

Management of endocrine disease: Secondary osteoporosis: pathophysiology and management

Osteoporosis is a skeletal disorder characterized by decreased mass and compromised bone strength predisposing to an increased risk of fractures. Although idiopathic osteoporosis is the most common form of osteoporosis, secondary factors may contribute to the bone loss and increased fracture risk in patients presenting with fragility fractures or osteoporosis. Several medical conditions and medications significantly increase the risk for bone loss and skeletal fragility. This review focuses on some of the common causes of osteoporosis, addressing the underlying mechanisms, diagnostic approach and treatment of low bone mass in the presence of these conditions.

Association between muscle hydration measures acquired using bioelectrical impedance spectroscopy and magnetic resonance imaging in healthy and hemodialysis population

Establishing the effect of fluctuating extracellular fluid (ECF) volume on muscle strength in people with end-stage renal disease (ESRD) on hemodialysis (HD) is essential, as inadequate hydration of the skeletal muscles impacts its strength and endurance. Bioelectrical impedance spectroscopy (BIS) has been a widely used method for estimating ECF volume of a limb or calf segment. Magnetic resonance imaging (MRI)-acquired transverse relaxation times (T2) has also been used for estimating ECF volumes of individual skeletal muscles. The purpose of this study was to determine the association between T2 (gold standard) of tibialis anterior (TA), medial (MG), and lateral gastrocnemius (LG), and soleus muscles and calf BIS ECF, in healthy and in people with ESRD/HD. Calf BIS and MRI measures were collected on two occasions before and after HD session in people with ESRD/HD and on a single occasion for the healthy participants. Linear regression analysis was used to establish the association between these measures. Thirty-two healthy and 22 participants on HD were recruited. The association between T2 of TA, LG, MG, and soleus muscles and ratio of calf BIS-acquired ECF and intracellular fluids (ICF) were: TA: β = 0.30, P > 0.05; LG: β = 0.37, P = 0.035; MG: β = 0.43, P = 0.014; soleus: β = 0.60, P < 0.001. For the HD group, calf ECF was significantly associated with T2 of TA (β = 0.44, P = 0.042), and medial gastrocnemius (β = 0.47, P = 0.027) following HD only. Hence BIS-acquired measures cannot be used to measure ECF volumes of a single muscle in the ESRD/HD population; however, BIS could be utilized to estimate ratio of ECF: ICF in healthy population for the LG, MG, and soleus muscles.

The clinical utility of FRAX to discriminate fracture status in men and women with chronic kidney disease

We assessed the ability of the World Health Organization's fracture risk assessment tool (FRAX), bone mineral density (BMD), and age to discriminate fracture status in adults with pre-dialysis chronic kidney disease (CKD). In adults with CKD, FRAX was able to discriminate fracture status but performed no better than BMD alone.

INTRODUCTION

Patients with CKD are at increased risk for fracture but the best method to assess fracture risk is not known.

METHODS

We assessed the ability of the World Health Organization's FRAX, compared with BMD at the femoral neck (FN), and age to discriminate fracture status (prevalent clinical nonspine and/or morphometric vertebral) in men and women, 18 years and older with pre-dialysis CKD. Results are presented as area under receiver operator characteristic curves (AUC) with 95% confidence intervals (CI).

RESULTS

We enrolled 353 subjects; mean age was 65 ± 14 years; weight was 79 ± 18 kg, and estimated glomerular filtration rate was 28 ml/min/1.73 m(2). About one third of the subjects had a prevalent clinical nonspine and/or morphometric vertebral fracture. FRAX was able to discriminate among those with prevalent clinical nonspine fractures (AUC, 0.72; 95% CI, 0.65-0.78), morphometric vertebral fractures (AUC, 0.66; 95% CI, 0.59-0.73), and any fracture (AUC, 0.71; 95% CI, 0.65-0.77). The discriminative ability of BMD at the FN alone was similar to FRAX for morphometric vertebral and any fractures; FRAX performed better than BMD for prevalent clinical nonspine fractures (AUC for BMD alone, 0.66; 95% CI, 0.60-0.73). Compared to FRAX, the AUC for age alone was lower for all fracture types.

CONCLUSIONS

Among men and women with CKD, FRAX is able to discriminate fracture status but performs no better than BMD alone.

Determination of bone architecture and strength in men and women with stage 5 chronic kidney disease

Fractures are common in men and women with dialysis-dependent chronic kidney disease (stage 5D CKD) and are associated with substantial morbidity and mortality. The clinical utility of dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT), noninvasive measures of bone mass and architecture that reflect fracture risk in healthy men and women, is uncertain in patients with stage 5D CKD. This review will outline the epidemiology and etiology of fractures and will summarize the published data that describe the association between fractures, bone mass, and bone strength in stage 5D CKD. Fracture risk assessment in stage 5D CKD is complicated as the etiology of fractures is multifactorial and includes impairments in bone quantity and quality. Cross-sectional data suggest that bone density by DXA is lower among stage 5D CKD patients with fractures compared with those without, and that this may be particularly true at cortical sites. However, DXA does not capture bone microarchitecture and cannot differentiate between cortical and trabecular bone. Some, but not all studies, that measure cortical and trabecular bone by pQCT in stage 5D CKD, demonstrate a preferential decrease in cortical bone; however, these studies are limited by small sample sizes and cross-sectional study design. No studies have reported on longitudinal relationships between bone architecture, strength, and incident fractures in patients with stage 5D CKD. Further research is needed to identify noninvasive measures of bone strength that can be used for fracture risk assessment in stage 5D CKD.

Fracture risk assessment in patients with chronic kidney disease

Fractures are common in patients with chronic kidney disease (CKD) and associated with substantially high morbidity and mortality. Bone mass measurements are commonly used to assess fracture risk in the general population, but the utility of these measurements in patients with CKD, and specifically among those on hemodialysis, is unclear. This review will outline the epidemiology and etiology of fractures in patients with CKD with a particular emphasis on men and women on hemodialysis. As well, we will summarize the published data, which describes the association between risk factors for fracture (including bone mass measurements, biochemical markers of mineral metabolism, and muscle strength) and fractures in patients with CKD. Patients with CKD suffer from fractures due to impairments in bone quantity, bone quality, and abnormalities of neuromuscular function. There is a paucity of evidence on the associations between bone quality, bone turnover markers, neuromuscular function, and fractures in patients with CKD. Furthermore, the complex etiology of fractures combined with the technical limitations of bone mineral density testing, both by dual energy X-ray absorptiometry (DXA) and by peripheral quantitative tomography (pQCT), limits the clinical utility of bone mass measurements for fracture prediction in CKD; this is particularly true among patients with stages 4 and 5 CKD. Further prospective studies to identify noninvasive measures of bone strength that can be used for fracture risk assessment are needed.

Fracture Risk Assessment in Chronic Kidney Disease, Prospective Testing Under Real World Environments (FRACTURE): a prospective study

Background

Chronic kidney disease (CKD) is associated with an increased risk of fracture. Decreased bone mass and disruption of microarchitecture occur early in the course of CKD and worsens with the progressive decline in renal function so that at the time of initiation of dialysis at least 50% of patients have had a fracture. Despite the excess fracture risk, and the associated increases in morbidity and mortality, little is known about the factors that are associated with an increase in fracture risk. Our study aims to identify prognostic factors for bone loss and fractures in patients with stages 3 to 5 CKD.

Methods

This prospective study aims to enroll two hundred and sixty men and women with stages 3 to 5 CKD. Subjects will be followed for 24 months and we will examine the ability of: 1) bone mineral density by dual x-ray absorptiometry at the spine, hip, and radius; 2) volumetric bone density by high resolution peripheral quantitated computed tomography at the radius and tibia; 3) serum markers of bone turnover; 4) bone formation rate by bone biopsy; and 5) muscle strength and balance to predict spine and non-spine fractures, identified by self-report and/or vertebral morphometry. All measurements will be obtained at baseline, at 12 and at 24 months with the exception of bone biopsy, which will be measured once at 12 months. Subjects will be contacted every 4 months to determine if there have been incident fractures or falls.

Discussion

This study is one of the first that aims to identify risk factors for fracture in early stage CKD patients. Ultimately, by identifying risk factors for fracture and targeting treatments in this group-before the initiation of renal replacement therapy - we will reduce the burden of disease due to fractures among patients with CKD.

Magnesium metabolism in health and disease

Magnesium (Mg) is the main intracellular divalent cation, and under basal conditions the small intestine absorbs 30-50% of its intake. Normal serum Mg ranges between 1.7-2.3 mg/dl (0.75-0.95 mmol/l), at any age. Even though eighty percent of serum Mg is filtered at the glomerulus, only 3% of it is finally excreted in the urine. Altered magnesium balance can be found in diabetes mellitus, chronic renal failure, nephrolithiasis, osteoporosis, aplastic osteopathy, and heart and vascular disease. Three physiopathologic mechanisms can induce Mg deficiency: reduced intestinal absorption, increased urinary losses, or intracellular shift of this cation. Intravenous or oral Mg repletion is the main treatment, and potassium-sparing diuretics may also induce renal Mg saving. Because the kidney has a very large capacity for Mg excretion, hypermagnesemia usually occurs in the setting of renal insufficiency and excessive Mg intake. Body excretion of Mg can be enhanced by use of saline diuresis, furosemide, or dialysis depending on the clinical situation.

INTRAOCULAR VIRAL AND IMMUNE PATHOGENESIS OF IMMUNE RECOVERY UVEITIS IN PATIENTS WITH HEALED CYTOMEGALOVIRUS RETINITIS

PURPOSE

To investigate immune and viral contributions to the pathogenesis of immune recovery uveitis (IRU), which presents as vitritis, macular edema, or formation of epiretinal membranes, and develops in patients with acquired immunodeficiency syndrome (AIDS) who experienced cytomegalovirus (CMV) retinitis before antiretroviral treatment (ART) induced immune reconstitution.

METHODS

Aqueous and vitreous fluids from patients with IRU, active CMV retinitis, and control human immunodeficiency virus (HIV)-negative, noninflamed eyes were compared for presence of cytokines IL-6, IL12, interferon gamma using enzyme-linked immunosorbent assay techniques, and CMV DNA (by polymerase chain reaction).

RESULTS

IRU eyes (11 patients, 18 samples) had the highest levels of IL-12 (median 48 pg/mL), moderate levels of IL-6 (median 146 pg/mL), and low but significant interferon gamma (median 15 pg/mL), compared to controls (P < 0.01). All uveitis eyes tested (9/9) were CMV DNA negative. In contrast, active CMV retinitis eyes were CMV DNA positive, had higher levels of IL-6 (median 349 pg/mL) (25 patients, 41 samples) than both control (P = 0.0001) and uveitis eyes (P = 0.048), similar levels of interferon gamma (median 27 pg/mL) to uveitis eyes, but less IL-12 (median 0 pg/mL) than uveitis eyes.

CONCLUSIONS

Inflammatory IRU can be differentiated from active CMV retinitis by the presence of IL-12, less IL-6, and absence of detectable CMV replication.

Osteoprotegerin (OPG) and receptor activator of NF-kB ligand (RANK-L) serum levels in patients on chronic hemodialysis

The mechanisms underlying the skeletal resistance to PTH in patients on chronic hemodialysis (CHD) are not yet fully clarified. Osteoprotegerin (OPG) and receptor activator of NF-kB ligand (RANK-L) modulate the genesis and activity of osteoclasts, however their role in renal osteodystrophy pathogenesis has not been clarified so far. The present study aimed to evaluate OPG and RANK-L serum levels in hemodialysis patients and whether OPG/RANK-L system could have a role in the skeletal resistance to PTH. In fasting blood samples obtained from 60 patients (36 males and 24 females) on CHD for at least 2 yr and from 40 healthy subjects of similar age and gender distribution as controls (CTRs), we measured serum OPG, RANK-L, bone alkaline phosphatase (B-ALP), N-terminal telopeptide of type I collagen (NTx), PTH(1-84), calcium and phosphate. In 30 of 60 hemodialysis patients, a blood sample was also drawn soon after the dialytic session. Serum levels of RANK-L, but not OPG, showed a slight but significant (p<0.05) decrease after the dialytic session. OPG resulted being about six times higher in CHD patients than in CTRs (38.7 +/- 16.2 vs 6.3 +/- 0.17 pg/ml), whereas RAN K-L serum levels were only slightly increased with respect to controls (0.88 +/- 0.47 vs 0.64 +/- 0.38 pmol/l). CHD patients showed serum PTH(1-84) and bone turnover higher than in CTRs. No correlation was found between OPG/RANK-L system and PTH or bone turnover markers. Instead, in the patients with high osteoclast activity (no.=21) OPG/RANK-L ratio was correlated (r=-0.41, p<0.01) with NTx serum levels, whereas in patients with decreased osteoclast activity (no.=39) no relationship was found. In conclusion, our findings showed that, although both OPG and RANK-L are accumulated in hemodialysis patients, only RANK-L and the balance between OPG and RANK-L seem to be related to osteoclast activity.

Localized jaw enlargement in renal osteodystrophy: report of a case and review of the literature

Renal osteodystrophy is a common long-term complication of end-stage renal disease. Involvement of the jaws is common and radiographic alterations are often one of the earliest signs of chronic renal disease. However, marked enlargement of the jaws is a rare complication of renal osteodystrophy. A case of localized asymptomatic enlargement of the mandible in a 38-year-old woman with chronic renal failure is presented. The clinical, radiographic, and histological findings were consistent with renal osteodystrophy. To our knowledge, this is the third case of localized mandibular enlargement of renal osteodystrophy reported in the English-language literature.

A new serum assay to measure N-terminal fragment of telopeptide of type I collagen in patients with renal osteodystrophy

BACKGROUND: Up until now, there was little known about the use of bone resorption markers in the assessment of bone status in patients with chronic renal failure (CRF). The present study evaluated the ability of a new immunoassay for N-terminal telopeptide of type I collagen to assess bone turnover in a group of hemodialyzed patients. METHODS: The following parameters were measured in a fasting blood sample from 111 patients on maintenance hemodialysis for at least 2 years and in 120 healthy subjects: calcium, phosphorus, magnesium, BALP, PTH, and N-terminal telopeptide of type I collagen (NTx-ELISA, OSTEOMARK NTx Siero-Ostex International). RESULTS: Serum PTH, BALP, and NTx were significantly higher (P<0.001) in hemodialyzed (HD) patients than in healthy subjects. In HD patients, PTH was correlated to BALP and NTx (r=0.40 and 0.55, respectively). When combining PTH and BALP serum levels, 17 patients showed high turnover (HT) and 65 were found to have a normal to low turnover (N-LT). In HT patients, serum NTx and dialytic age were significantly (P<0.01) higher than in N-LT patients. Moreover, even after adjusting for age, body mass index, dialytic age, and calcium-vitamin D treatment, serum NTx discriminated between HT and N-LT with a sensitivity of 97.6% and a specificity of 90.9%. CONCLUSION: Although bone biopsy remains the reference method for the diagnosis of renal osteodystrophy, the combined use of markers of bone resorption and bone formation could improve the clinical management of renal bone diseases.

Paradoxical activity of CMV retinitis in patients receiving highly active antiretroviral therapy

PURPOSE

To report two types of atypical behaviors of cytomegalovirus (CMV) retinitis in the highly active antiretroviral therapy (HAART) era, including active CMV retinitis in the presence of persistently high CD4 cell counts during HAART and CMV retinitis that has not reactivated despite persistently low CD4 cell counts.

METHODS

Prospective, longitudinal, observational study of a cohort of 116 patients with acquired immunodeficiency syndrome who had a history of CMV retinitis during the HAART era.

RESULTS

Sixty (52%) of the 116 patients with acquired immunodeficiency syndrome and CMV retinitis were HAART responders. Subsequently, HAART failed for 9 of the 60 patients with low CD4 cell counts. Of these 9 patients, 5 developed reactivation of CMV retinitis, and 4 remained free of CMV retinitis despite CD4 cell counts of <50/microL and lack of anti-CMV therapy. Paradoxically, there was a patient with a documented median CD4 cell count of 204/microL for 19 months who had newly diagnosed active CMV retinitis.

CONCLUSION

In the HAART era, CMV retinitis may remain quiescent despite extremely low CD4 cell counts, and rarely, CMV retinitis may become active in the setting of persistently high CD4 cell counts in a subset of HAART responders.

Bone density and heel ultrasound testing do not identify patients with dialysis-dependent renal failure who have had fractures

Patients with dialysis-dependent renal failure are at increased risk for low-trauma fractures. However, the optimal means of identifying patients at high risk for fracture is not known. We assessed the association between fracture history and two tests of bone mineral density (dual x-ray absorptiometry [DEXA] and calcaneal ultrasound) among patients with hemodialysis-dependent renal failure. We evaluated 71 men and 33 women aged 55 years or older who had been receiving hemodialysis for at least 1 year. All patients underwent spinal radiography, DEXA of the hip and lumbar spine, and calcaneal ultrasonography. We assessed risk factors for low-trauma fractures by questionnaire and medical chart review. Of patients, 52% had a fracture on spinal radiographs or a history of a low-trauma fracture, 69% had osteopenia by DEXA, and 26% had a low heel ultrasound measurement. Neither DEXA nor calcaneal ultrasound was associated with fracture history, however. Our findings indicate that fractures among patients with dialysis-dependent renal failure are common. Tests of bone strength do not adequately identify patients with a history of fractures. Prospective studies to determine the optimal method of identifying patients with dialysis-dependent renal failure at high risk for fracture are needed.

Is there an optimal parathyroid hormone level in end-stage renal failure: the lower the better?

Skeletal resistance to parathyroid hormone is well defined in patients with chronic renal failure. In recent years, with the increased frequency of development of adynamic bone disease, it has been recognized that secondary hyperparathyroidism must exist as a 'trade off' mechanism to maintain skeletal bone remodeling in this patient population. An optimal level of intact parathyroid hormone to maintain the normal skeletal bone turnover is believed to be between 2.0 and 2.5 times the upper limit of normal parathyroid hormone. It has very recently been argued that the optimal parathyroid hormone level for maintenance of skeletal bone remodeling may be insufficient to prevent the extraskeletal complications of coronary artery calcifications, calcific valvular heart disease, and cardiac death. To provide optimal health care for these patients several new treatments have been developed, including use of new vitamin D analogs, calcimimetic agents, and noncalcium-based phosphorus binders. It is anticipated that with lower suppression of parathyroid hormone by these vitamin D analogs, intermittent suppression of parathyroid hormone with calcimimetic agents, and the use of noncalcium phosphorus binders (Renageltrade) by regulating serum calcium, the resultant phosphorus concentrations will provide an optimal parathyroid hormone activity to maintain skeletal bone remodeling, while preventing extraskeletal complications.