Pathogenic, clinical, and therapeutic aspects of secondary hyperparathyroidism in chronic renal failure

What Each Clinical Anatomist Has to Know about Left Renal Vein Entrapment Syndrome (Nutcracker Syndrome): A Review of the Most Important Findings

Nutcracker syndrome (NCS) is the most common term for compression of the left renal vein between the superior mesenteric artery and the abdominal aorta. The development of NCS is associated with the formation of the left renal vein (LRV) from the aortic collar during the sixth to eighth week of gestation and abnormal angulation of the superior mesenteric artery from the aorta. Collateralization of venous circulation is the most significant effect of NCS. It includes mainly the left gonadal vein and the communicating lumbar vein. Undiagnosed NCS may affect retroperitoneal surgery and other radiological and vascular procedures. The clinical symptoms of NCS may generally be described as renal presentation when symptoms like haematuria, left flank pain, and proteinuria occur, but urologic presentation is also possible. Radiological methods of confirming NCS include Doppler ultrasonography as a primary test, retrograde venography, which can measure the renocaval pressure gradient, computed tomography angiography, which is faster and less traumatic, intravascular ultrasound, and magnetic resonance angiography. Treatment can be conservative or surgical, depending on the severity of symptoms and degree of LRV occlusion. Nutcracker syndrome is worth considering especially in differential diagnosis of haematuria of unknown origin.

Successful Conversion From Parenteral Paricalcitol to Pulse Oral Calcitriol for the Management of Secondary Hyperparathyroidism in Hemodialysis Patients

OBJECTIVE

The management of hyperparathyroidism in hemodialysis patients involves the administration of phosphate binders, vitamin D receptor activators, and calcimimetics. Intravenous paricalcitol has been preferred over oral calcitriol as it may cause less hypercalcemia and hyperphosphatemia. However, there is little data looking at the efficacy and tolerability of oral calcitriol in the calcimimetic era particularly in a real practice-based experience. The University of California, Irvine free-standing dialysis center converted from routine intravenous paricalcitol to oral calcitriol due to pharmacy purchasing preferences. We report the efficacy, safety, and cost of such a change.

SUBJECTS

Ninety-three preconversion intravenous paricalcitol and 91 postconversion oral calcitriol.

INTERVENTION

Conversion to in-center, pulse, oral calcitriol (0.25 mcg = 1 mcg paricalcitol) 3 times a week from intravenous paricalcitol. Additional dose adjustments were made by the nephrologists based on clinical indications.

MAIN OUTCOME MEASURE

Five-month average serum calcium, phosphorous, and intact parathyroid hormone levels and cardiovascular events pretransition and posttransition.

RESULTS

There were 93 patients on intravenous paricalcitol between April 2013 and August 2013, of which 74 converted to oral calcitriol and were included in the postconversion group evaluated between October 2013 and February 2014. An additional 17 new patients had initiated calcitriol such that 91 patients were on oral therapy in the postconversion period. Sevelamer use increased from 41 (44.1%) patients preconversion to 48 (52.7%) postconversion, whereas calcium acetate use significantly dropped from 62 (66.7%) to 46 (50.5%) (P = .026). Cinacalcet use dropped slightly from 37 (39.7%) patients preconversion to 35 (38.4%) postconversion. Average serum calcium, phosphorus, and intact parathyroid hormone levels remained unchanged after conversion. Percent of values within Kidney Disease Outcome Quality Initiative guidelines were similarly maintained. Estimated vitamin D cost savings were $564 per person/year. No increase in the incidence of cardiovascular events was observed.

CONCLUSIONS

We conclude that in-center distributed pulse oral calcitriol may be an effective, safe, and economical treatment option for the management of hyperparathyroidism in hemodialysis patients.

Minimal Change Disease as a Secondary and Reversible Event of a Renal Transplant Case with Systemic Lupus Erythematosus

Secondary causes of minimal change disease (MCD) account for a minority of cases compared to its primary or idiopathic form and provide ground for consideration of common mechanisms of pathogenesis. In this paper we report a case of a 27-year-old Latina woman, a renal transplant recipient with systemic lupus erythematosus (SLE), who developed nephrotic range proteinuria 6 months after transplantation. The patient had recurrent acute renal failure and multiple biopsies were consistent with MCD. However, she lacked any other features of the typical nephrotic syndrome. An angiogram revealed a right external iliac vein stenosis in the region of renal vein anastomosis, which when restored resulted in normalization of creatinine and relief from proteinuria. We report a rare case of MCD developing secondary to iliac vein stenosis in a renal transplant recipient with SLE. Additionally we suggest that, in the event of biopsy-proven MCD presenting as an atypical nephrotic syndrome, alternative or secondary, potentially reversible, causes should be considered and explored.

Serum 25-hydroxyvitamin D level and kidney function decline in a Swiss general adult population

BACKGROUND AND OBJECTIVES

Molecular evidence suggests that levels of vitamin D are associated with kidney function loss. Still, population-based studies are limited and few have considered the potential confounding effect of baseline kidney function. This study evaluated the association of serum 25-hydroxyvitamin D with change in eGFR, rapid eGFR decline, and incidence of CKD and albuminuria.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline (2003-2006) and 5.5-year follow-up data from a Swiss adult general population were used to evaluate the association of serum 25-hydroxyvitamin D with change in eGFR, rapid eGFR decline (annual loss >3 ml/min per 1.73 m(2)), and incidence of CKD and albuminuria. Serum 25-hydroxyvitamin D was measured at baseline using liquid chromatography-tandem mass spectrometry. eGFR and albuminuria were collected at baseline and follow-up. Multivariate linear and logistic regression models were used considering potential confounding factors.

RESULTS

Among the 4280 people included in the analysis, the mean±SD annual eGFR change was -0.57±1.78 ml/min per 1.73 m(2), and 287 (6.7%) participants presented rapid eGFR decline. Before adjustment for baseline eGFR, baseline 25-hydroxyvitamin D level was associated with both mean annual eGFR change and risk of rapid eGFR decline, independently of baseline albuminuria. Once adjusted for baseline eGFR, associations were no longer significant. For every 10 ng/ml higher baseline 25-hydroxyvitamin D, the adjusted mean annual eGFR change was -0.005 ml/min per 1.73 m(2) (95% confidence interval, -0.063 to 0.053; P=0.87) and the risk of rapid eGFR decline was null (odds ratio, 0.93; 95% confidence interval, 0.79 to 1.08; P=0.33). Baseline 25-hydroxyvitamin D level was not associated with incidence of CKD or albuminuria.

CONCLUSIONS

The association of 25-hydroxyvitamin D with eGFR decline is confounded by baseline eGFR. Sufficient 25-hydroxyvitamin D levels do not seem to protect from eGFR decline independently from baseline eGFR.

[Pharmaceutical therapy of bone metabolism disorders in chronic kidney disease mineral bone disorder (CKD-MBD) with special respect to antiresorptive substances]

Disturbances in bone and mineral turnover are common complications in patients with impaired renal function. Besides an increased risk for cardiovascular events they promote skeletal events, such as bone pain and fractures. Evidence for the antifracture efficacy of antiresorptive and osteoanabolic treatment strategies has only been demonstrated for patients with osteoporosis. The use of osteotropic drugs in patients with impaired renal function requires large randomized placebo-controlled trials.

Mineral metabolic abnormalities and mortality in dialysis patients

The survival rate of dialysis patients, as determined by risk factors such as hypertension, nutritional status, and chronic inflammation, is lower than that of the general population. In addition, disorders of bone mineral metabolism are independently related to mortality and morbidity associated with cardiovascular disease and fracture in dialysis patients. Hyperphosphatemia is an important risk factor of, not only secondary hyperparathyroidism, but also cardiovascular disease. On the other hand, the risk of death reportedly increases with an increase in adjusted serum calcium level, while calcium levels below the recommended target are not associated with a worsened outcome. Thus, the significance of target levels of serum calcium in dialysis patients is debatable. The consensus on determining optimal parathyroid function in dialysis patients, however, is yet to be established. Therefore, the contribution of phosphorus and calcium levels to prognosis is perhaps more significant. Elevated fibroblast growth factor 23 levels have also been shown to be associated with cardiovascular events and death. In this review, we examine the associations between mineral metabolic abnormalities including serum phosphorus, calcium, and parathyroid hormone and mortality in dialysis patients.

Fungal granulomatous interstitial nephritis presenting as acute kidney injury diagnosed by renal histology including PCR assay

We describe two cases of fungal granulomatous interstitial nephritis (GIN) presenting as acute kidney injury (AKI). Increased serum creatinine was detected in Patient 1 after chemotherapy for pharyngeal cancer and in Patient 2 after steroid pulse therapy for bronchial asthma. Renal histology of both patients revealed GIN. Polymerase chain reaction (PCR)-based detection of fungal DNA sequences from kidney tissue demonstrated Trichosporon laibachii and Candida albicans, respectively. When AKI occurs in an immunocompromised host, differential diagnosis of fungal interstitial nephritis should be considered. Furthermore, PCR-based detection of fungal DNA sequences from renal specimens can be useful for rapid diagnosis.

Varicocele and nutcracker syndrome: sonographic findings

OBJECTIVE

Varicocele is a vascular lesion commonly associated with infertility. Its etiology is only partly understood; hence, the purpose of the study was to establish its correlation with intrinsic anatomic differences and nutcracker syndrome.

METHODS

A total of 93 patients with varicocele and 76 patients without varicocele were enrolled. The diagnosis of varicocele was based on physical examination, followed by sonographic evaluation of the hilar portion and aortomesenteric portion (AMP) of the left renal vein (LRV). The anteroposterior diameter in millimeters and peak flow in centimeters per second in each region were measured.

RESULTS

A total of 28 patients with the nutcracker syndrome were identified in the study group (30.10%), and 2 were identified in the control group (2.63%). The mean diameters of the hilar portion and AMP of the LRV were significantly different in varicocele-affected patients compared with the control group (P < .0001 for both). The mean peak velocities in the hilar portion and AMP were significantly different in patients with varicocele (P < .0001). Patients with varicocele and nutcracker syndrome did not have a significant difference in either the hilar or AMP diameter compared with patients with varicocele without nutcracker syndrome. They had a significant difference in both the hilar and AMP peak flow velocity (P = .0001 for both).

CONCLUSIONS

Our findings indicate that nutcracker syndrome is a frequent finding in varicocele-affected patients and should be routinely excluded as a possible cause of varicocele. In addition, intrinsic anatomic differences in the AMP and hilar portion of the LRV could be directly responsible for the onset of varicocele.

The vitamin D system: a crosstalk between the heart and kidney

Chronic kidney disease (CKD) independently increases the rates of cardiovascular disease, whereas the severity of kidney disease correlates with increased cardiovascular morbidity and death. Vitamin D is modified in the liver and the kidney to its active form (1,25-dihydroxyvitamin D) by the 25-hydroxy vitamin D 1-hydroxylase enzyme (CYP27B1). The activated vitamin D brings about its actions through the vitamin D receptor (VDR). The VDRs and CYP27B1 have recently been shown to be expressed in several tissues, not directly involved in mineral homeostasis, including the cardiovascular, immune, and epithelial systems. The action of vitamin D in these tissues is implicated in the regulation of endothelial, vascular smooth muscle, and cardiac cell function, the renin-angiotensin system, inflammatory and fibrotic pathways, and immune response. Impaired VDR activation and signalling results in cellular dysfunction in several organs and biological systems, which leads to reduced bone health, an increased risk for epithelial cancers, metabolic disease, and uncontrolled inflammatory responses. Failure of cardiovascular VDR activation results in hypertension, accelerated atherosclerosis and vascular calcification, cardiac hypertrophy with vascular rarification and fibrosis, and progressive renal dysfunction. An emerging body of evidence has prompted attention to the relationship between CKD, mineral bone disorder (CKD-MBD), and cardiovascular disease in the new guidelines from Kidney Disease: Improving Global Outcomes. Vitamin D receptor activators, commonly used to treat CKD-MBD, and an appropriate treatment of vitamin D hormonal system failure in patients with CKD, may help to reduce cardiovascular morbidity and mortality in these patients.

Impact of secondary hyperparathyroidism on disease progression, healthcare resource utilization and costs in pre-dialysis CKD patients

BACKGROUND AND OBJECTIVES

Secondary hyperparathyroidism (SHPT) can lead to significant morbidity, mortality, and additional healthcare resource utilization in chronic kidney disease (CKD) stage 5. The objective of this study was to examine healthcare costs and utilization, and the risks of dialysis or mortality, among pre-dialysis CKD patients with and without SHPT.

RESEARCH DESIGN AND METHODS

This retrospective cohort study examined insurance claims from 66 644 adult, pre-dialysis, CKD patients with and without SHPT during a 72-month period. Annualized estimates of healthcare costs and utilization, and disease progression to dialysis or death following index CKD diagnosis were compared.

RESULTS

Post-index annualized costs and inpatient healthcare resource utilization was higher in those with SHPT in both unadjusted and adjusted (controlling for gender, age, plan type, payer type, geographic region, physician specialty, pre-index co-morbidities, and pre-index total healthcare costs), and unmatched and matched analyses. Kaplan-Meier analysis demonstrated that the rate of progression to dialysis or death was higher for CKD with SHPT compared to CKD without SHPT, and Cox proportional hazard models suggested that CKD patients with SHPT were more than four to five times as likely to initiate dialysis or die as compared to CKD without SHPT.

CONCLUSION

SHPT in pre-dialysis CKD patients is associated with significantly greater healthcare costs, inpatient hospitalizations, and a faster rate of disease progression compared to pre-dialysis CKD without SHPT. Since observational studies are designed to demonstrate associations rather than causality, further investigation is required to confirm these findings.

Prevalence and severity of disordered mineral metabolism in Blacks with chronic kidney disease

Disorders of mineral metabolism develop early in chronic kidney disease, but it appears that Blacks with stage-5 disease have more severe secondary hyperparathyroidism than other races. We measured levels of parathyroid hormone, calcium, phosphorus, 25-hydroxyvitamin D (25D) and 1,25-dihydroxyvitamin D (1,25D) in 227 Black and 1633 non-Black participants in the SEEK study, a multi-center cohort of patients with early chronic kidney disease. Overall, Blacks had similar 1,25D levels compared with non-Blacks, but significantly lower levels of 25D with higher levels of calcium, phosphorus, and parathyroid hormone, and were significantly more likely to have hyperphosphatemia than non-Blacks. In multivariable analyses adjusted for age, gender, estimated glomerular filtration rate, body mass index, and diabetes, Blacks had significantly lower 25D and higher parathyroid hormone levels than non-Blacks, with the latter parameter remaining significant after further adjustment for calcium, phosphorus, 25D, and 1,25D. The association between Black race and secondary hyperparathyroidism, independent of known risk factors, suggests that novel mechanisms contribute to secondary hyperparathyroidism in Blacks with chronic kidney disease.

Review of dialysate calcium concentration in hemodialysis

The dialysate calcium (Ca) concentration for hemodialysis (HD) patients can be adjusted to manage more optimally the body's Ca and phosphate balance, and thus improve bone metabolism as well as reduce accelerated arteriosclerosis and cardiovascular mortality. The appropriate dialysate Ca concentration allowing this balance should be prescribed to each individual patient depending on a multitude of variable factors relating to Ca load. A lower dialysate Ca concentration of 1.25 to 1.3 mmol/L will permit the use of vitamin D supplements and Ca-based phosphate binders in clinical practice, with much less risk of Ca loading and resultant hypercalcemia and calcification. Low Ca baths are useful in the setting of adynamic bone disease where an increase in bone turnover is required. However, low Ca levels in the dialysate may also predispose to cardiac arrhythmias and hemodynamically unstable dialysis sessions with intradialytic hypotension. Higher Ca dialysate is useful to sustain normal serum Ca levels where patients are not taking Ca-based binders or if Ca supplements are not able to normalize serum levels. Suppression of hyperparathyroidism is also effective with dialysate Ca of 1.75 mmol/L, but hypercalcemia, metastatic calcification, and oversuppression of parathyroid hormone are risks. Dialysate Ca of 1.5 mmol/L may be a compromise between bone protection and reduction in cardiovascular risk for conventional HD and is a common concentration used throughout the world. The increase in longer, more frequent dialysis such as short-daily and nocturnal HD, however, provides another challenge with regard to optimal dialysate Ca levels and higher levels of 1.75 mmol/L are probably indicated in this setting. Difficulties in determining the ideal dialysate Ca occur because of the complex pathophysiology of bone and mineral metabolism in HD patients and there needs to be a balance between dialysis prescription and other treatment modalities. To optimize management of the abnormal Ca balance, other aspects of this disorder need to be more fully clarified and, with evolving medications for phosphate control and treatment of secondary hyperparathyroidism, as well as the emergence of a multitude of different HD regimes, further studies are required to make definitive recommendations. At present, we need to maintain flexibility with HD treatments and so dialysate Ca needs to be individualized to meet the specific requirements of patients by optimizing management of renal bone disease and simultaneously reducing metastatic calcification and cardiovascular disease.

VITAMIN D IN HEALTH AND DISEASE: Beyond Minerals and Parathyroid Hormone: Role of Active Vitamin D in End-Stage Renal Disease

Secondary hyperparathyroidism is a common complication of end-stage renal disease (ESRD) that is often treated with activated forms of intravenous vitamin D. The natural course and treatment of secondary hyperparathyroidism in hemodialysis patients is punctuated by episodes of hypercalcemia, hyperphosphatemia, and increased calcium-phosphate product, which in previous studies were linked to increased mortality. Historically these episodes have been attributed to vitamin D, leading some authorities to favor decreased vitamin D use. However, the studies that examined the impact of mineral levels and parathyroid hormone (PTH) on survival did not consistently account for vitamin D therapy itself on hemodialysis patient survival. The current review examines in detail two recent large-scale studies of hemodialysis patients: one that demonstrated a survival advantage of paricalcitol over calcitriol and a second that demonstrated a significant survival advantage of any intravenous vitamin D formulation versus none. In both studies, the effects were independent of mineral and PTH levels, suggesting "nontraditional" actions of vitamin D contributed to the observed survival advantage. Several of these nontraditional actions are reviewed with an emphasis on those that might impact hemodialysis outcomes.

Inhibition of human intestinal brush border membrane vesicle Na+-dependent phosphate uptake by phosphophloretin derivatives

Hyperphosphatemia and II(o) hyperparathyroidism are common and severe complications of chronic renal failure. Reduced dietary phosphorus has been shown to be an effective treatment in reducing serum phosphate and serum PTH. 2(')-Phosphophloretin inhibited small intestine apical membrane Na(+)/phosphate cotransport and reduced serum phosphate in adult rats. 2(')-PP and phosphoesters of phloretin were tested for inhibition of human small intestine brush border membrane alkaline phosphatase activity and for inhibition of Na(+)-dependent phosphate uptake. The IC(50)'s for inhibition of alkaline phosphatase suggested an order of inhibitory potency of 4-PP > phloretin > 4(')-PP > 2(')-PP. Inhibition of Na(+)-dependent phosphate uptake followed the sequence 2(')-PPz.Gt;4(')-PP > 4-PP > phloretin. These results are consistent with 2(')-PP being a specific inhibitor of human intestinal brush border membrane Na(+)/phosphate cotransport.

A phosphorylated phloretin derivative. Synthesis and effect on intestinal Na(+)-dependent phosphate absorption

2'-Phosphophloretin (2'-PP), a phosphorylated derivative of the plant chalcone, was synthesized. The effect of 2'-PP, on Na(+)-dependent phosphate uptake into intestinal brush-border membrane vesicles (BBMV) isolated from rabbit and rat duodenum and jejunum was examined. 2'-PP decreased Na(+)-dependent phosphate uptake into rabbit BBMV with an IC(50) of 55 nM and into rat BBMV with an IC(50) of 58 nM. 2'-PP did not affect Na(+)-dependent glucose, Na(+)-dependent sulfate, or Na(+)-dependent alanine uptake by rabbit intestinal BBMVs. 2'-PP inhibition of rabbit intestinal BBMV Na(+)-dependent phosphate uptake was sensitive to external phosphate concentration, suggesting that 2'-PP inhibition of Na(+)-dependent phosphate uptake was competitive with respect to phosphate. Binding of [(3)H]2'-PP to rabbit intestinal BBMV was examined. Binding of [(3)H]2'-PP was Na(+)-dependent with a K(0.5) for Na(+)(Na(+) concentration for 50% 2'-PP binding) of 30 mM. The apparent K(s) for Na(+)-dependent [(3)H]2'-PP binding to rabbit BBMVs was 58 nM in agreement with the IC(50) for 2'-PP inhibition of Na(+)-dependent phosphate uptake. These results indicate that 2'-PP bound to rabbit or rat intestinal BBMV Na(+)-phosphate cotransporter and inhibited Na(+)-dependent phosphate uptake. In rats treated with 2'-PP by daily gavage, the effect of 2'-PP on serum phosphate, serum glucose, and serum calcium was examined. In a concentration-dependent manner, 2'-PP reduced serum phosphate by 45% 1 wk after starting treatment. 2'-PP did not alter serum calcium or serum glucose. The apparent IC(50) for 2'-PP in vivo was 3 microM.

The role of vitamin D in mild to moderate chronic kidney disease

Dietary vitamin D is a prohormone that is metabolized to the bioactive vitamin D hormone, 1 alpha, 25-dihydroxyvitamin D [1,25-(OH)2D]. 1,25-(OH)2D has been implicated in a variety of regulatory pathways that extend well beyond its traditional function in Ca2+ homeostasis. In uncovering these diverse functions, investigators have focused on the complex interaction between 1,25-(OH)2D and parathyroid hormone (PTH). Here, we present an overview of the functions of vitamin D hormone and PTH in the clinical context of secondary hyperparathyroidism. We discuss recent developments in treatment that address imbalances in vitamin D hormone and PTH levels, supporting the argument that early intervention can reduce the risk of metabolic complications caused by vitamin D hormone deficiency in patients with chronic kidney disease.

Different Mg to Fe ratios in the mixed metal MgFe hydroxy-carbonate compounds and the effect on phosphate binding compared with established phosphate binders

Due to the side effects of the current oral phosphate binders, there is a need for effective alternatives. A number of mixed metal hydroxy-carbonate compounds (MMHCs) based on Mg and Fe have recently been established as effective phosphate binders. We have now carried out further studies on the MMHCs with different ratios of Mg(2+):Fe(3+) in different forms to assess for phosphate binding efficacy and ionic release in aqueous solution and food slurries. The compounds that provide the most promise are those with Mg(2+):Fe(3+) ratios of 2:1 and 4:1 in the unaged/dry form. Their phosphate binding efficacy was compared with a wide range of established phosphate binders, such as aluminum hydroxide [Al(OH)(3)], calcium carbonate (CaCO(3)), calcium acetate (CaAc(2)), magnesium hydroxide [Mg(OH)(2)], and lanthanum carbonate [La(2)(CO(3))(3)] in various food slurries. The results showed that the MgFe compounds were much more effective (on a weight for weight basis) than the established binders, and their properties were relatively pH independent. Calcium compounds (CaCO(3) and CaAc(2)) were ineffective under the experimental conditions. Mg(OH)(2) was effective at low pH but not at pHs greater than 5.0, and also released two- to threefold more magnesium than the MgFe compounds. Al(OH)(3) showed some degree of efficacy, but the binding capacity was, at best, less than 50% of the MMHCs. La(2)(CO(3))(3) required at least a 10-fold increase in weight to give comparable binding to the MMHCs. In conclusion, MgFe hydroxy-carbonate compounds are effective phosphate binders and may provide a better alternative to both existing and emerging binders for combating hyperphosphataemia.

Cost-effectiveness of sevelamer versus calcium carbonate plus atorvastatin to reduce LDL in patients with chronic renal insufficiency with dyslipidemia and hyperphosphatemia

We conducted a cost-effectiveness analysis to compare costs and clinical outcomes of sevelamer versus calcium carbonate plus atorvastatin for treatment of dyslipidemia in patients with chronic renal insufficiency. The model was from the third-party payer perspective. Efficacy and adverse event rates for each regimen were obtained from published clinical trials. Drug costs were based on average wholesale prices; monitoring costs were based on Medicare reimbursement rates. Our model suggests that the combination of calcium carbonate plus atorvastatin is substantially more cost-effective than sevelamer in reducing low-density lipoprotein (LDL) in these patients. One-way sensitivity analyses were performed to assess if 25% and 50% price reductions in sevelamer affected overall cost-effectiveness results. A 50% sevelamer price reduction was less expensive than combination therapy but remained less cost-effective. A two-way sensitivity analysis on the probability that a patient achieves the goal of a 35% LDL reduction resulted in calcium carbonate plus atorvastatin remaining more cost-effective. Further cost-effectiveness studies are necessary to corroborate our data.