Evidence for skeletal resistance to parathyroid hormone in magnesium deficiency. Studies in isolated perfused bone

Skeletal parathyroid hormone hyporesponsiveness: a neglected, but clinically relevant reality in chronic kidney disease

PURPOSE OF REVIEW

Defining the optimal parathyroid hormone (PTH) target in chronic kidney disease (CKD) is challenging, especially for bone outcomes, due to the substantial variability in the skeleton's response to PTH. Although PTH hyporesponsiveness is as integral a component of CKD-mineral bone disorder as elevated PTH levels, clinical awareness of this condition is limited. In this review, we will discuss factors and mechanisms contributing to PTH hyporesponsiveness in CKD. This knowledge may provide clues towards a personalized approach to treating secondary hyperparathyroidism in CKD.

RECENT FINDINGS

Indicates a link between disturbed phosphate metabolism and impaired skeletal calcium sensing receptor signaling as an important mediator of PTH hyporesponsiveness in CKD. Further, cohort studies with diverse populations point towards differences in mineral metabolism control, rather than genetic or environmental factors, as drivers of the variability of PTH responsiveness.

IN SUMMARY

Skeletal PTH hyporesponsiveness in CKD has a multifactorial origin, shows important interindividual variability, and is challenging to estimate in clinical practice. The variability in skeletal responsiveness compromises PTH as a biomarker of bone turnover, especially when considering populations that are heterogeneous in ethnicity, demography, kidney function, primary kidney disease and mineral metabolism control, and in patients treated with bone targeting drugs.

Magnesium and Fracture Risk in the General Population and Patients Receiving Dialysis: A Narrative Review

Purpose of Review

Magnesium is an essential mineral for bone metabolism, but little is known about how magnesium intake alters fracture risk. We conducted a narrative review to better understand how magnesium intake, through supplementation, diet, or altering the concentration of dialysate magnesium, affects mineral bone disease and the risk of fracture in individuals across the spectrum of kidney disease.

Sources of Information

Peer-reviewed clinical trials and observational studies.

Methods

We searched for relevant articles in MEDLINE and EMBASE databases. The methodologic quality of clinical trials was assessed using a modified version of the Downs and Black criteria checklist.

Key Findings

The role of magnesium intake in fracture prevention is unclear in both the general population and in patients receiving maintenance dialysis. In those with normal kidney function, 2 meta-analyses showed higher bone mineral density in those with higher dietary magnesium, whereas 1 systematic review showed no effect on fracture risk. In patients receiving maintenance hemodialysis or peritoneal dialysis, a higher concentration of dialysate magnesium is associated with a lower concentration of parathyroid hormone, but little is known about other bone-related outcomes. In 2 observational studies of patients receiving hemodialysis, a higher concentration of serum magnesium was associated with a lower risk of hip fracture.

Limitations

This narrative review included only articles written in English. Observed effects of magnesium intake in the general population may not be applicable to those with chronic kidney disease particularly in those receiving dialysis.

Hungry bone syndrome after parathyroid surgery

INTRODUCTION

Data on the incidence rates of hungry bone syndrome after parathyroidectomy in patients on dialysis are inconsistent, as the published rates vary from 15.8% to 92.9%.

METHODS

Between 2009 and 2019, 120 hemodialysis patients underwent parathyroidectomy for secondary hyperparathyroidism at the Chang Gung Memorial Hospital. The patients were stratified into two groups based on the presence (n = 100) or absence (n = 20) of hungry bone syndrome after parathyroidectomy.

FINDINGS

Subtotal parathyroidectomy was the most common surgery performed (76.7%), followed by total parathyroidectomy with autoimplantation (23.3%). Pathological examination revealed parathyroid hyperplasia. Hungry bone syndrome developed within 0.3 ± 0.3 months and lasted for 11.1 ± 14.7 months. After surgery, compared with patients without hungry bone syndrome, patients with hungry bone syndrome had lower levels of nadir corrected calcium (P < 0.001), as well as lower nadir (P < 0.001) and peak (P < 0.001) intact parathyroid hormone levels. During 59.3 ± 44.0 months of follow-up, persistence and recurrence of hyperparathyroidism occurred in 25 (20.8%) and 30 (25.0%) patients, respectively. Furthermore, patients with hungry bone syndrome had a lower rate of persistent hyperparathyroidism than those without hungry bone syndrome (P < 0.001). Four patients (3.3%) underwent a second parathyroidectomy. Patients with hungry bone syndrome received fewer second parathyroidectomies than those without hungry bone syndrome (P < 0.001). Finally, a multivariate logistic regression model revealed that the preoperative blood ferritin level was a negative predictor of the development of hungry bone syndrome (P = 0.038).

DISCUSSION

Hungry bone syndrome is common (83.3%) after parathyroidectomy for secondary hyperparathyroidism in patients undergoing hemodialysis, and this complication should be monitored and managed appropriately.

Influencing factors of serum magnesium in CKD5 patients: A multicenter study in southern China

INTRODUCTION

Magnesium (Mg) disturbances are related to cardiac, bone, and renal patient mortality. In this study, we compared biochemical markers in hemodialysis (HD) and peritoneal dialysis (PD) patients and explored the influencing factors of serum Mg in stage 5 chronic kidney disease (CKD5) patients.

MATERIAL AND METHODS

All 598 patients with CKD5 from three medical centers in South China were recruited into this prospective cohort study from March 1, 2018, to January 31, 2021. Our study recorded the clinical characteristics and laboratory data of the patients.

RESULTS

Hemodialysis patients (0.99 ± 0.19 mmol/L) had a higher mean serum Mg level than PD patients (0.86 ± 0.20 mmol/L; p < 0.01). Regression analysis showed that only corrected calcium (Ca), phosphate (P), Ca/Mg, Ca × P, albumin (Alb), total protein and creatine (Cr) predicted Mg levels in CKD5 patients (p < 0.01). Ca/Mg predicts hypomagnesemia with 78% sensitivity and 85% specificity in CKD5 patients. The AUC value corresponding to Ca/Mg was 0.88.

CONCLUSIONS

This multicenter study in southern China showed that for all CKD5 patients, corrected Ca and Alb had a significant positive effect on serum Mg, while Ca/Mg had a significant negative effect on serum Mg. In 123 HD patients, Ca × P was positively associated with Mg while Ca/Mg and P were negatively associated with Mg. In 398 PD patients, Ca × P, Alb, and total protein were positively associated with Mg while Ca/Mg and P were negatively associated with Mg. In 77 non-dialysis patients, corrected Ca, Cr, and total protein were positively associated with Mg while Ca/Mg was negatively associated with Mg. Furthermore, Ca/Mg might be another useful technique to monitor blood Mg levels in CKD5 patients.

CLINICAL TRIAL REGISTRATION

ChiCTR1800014557.

The Perilous PPI: Proton Pump Inhibitor as a Cause of Clinically Significant Hypomagnesaemia

Proton pump inhibitors (PPIs) are the mainstay of therapy for all gastric acid related diseases and are commonly used in current clinical practice. Although widely regarded as safe, PPIs have been associated with a variety of adverse effects, including hypomagnesaemia. The postulated mechanism of PPI-related hypomagnesaemia involves inhibition of intestinal magnesium absorption via transient receptor potential melastin (TRPM) 6 and 7 cation channels. PPIinduced hypomagnesaemia (PPIH) has become a well recognized phenomenon since it was first reported in 2006. Clinical concerns arise from growing number of case reports presenting PPIH as a consequence of long-term PPI use, with more than 30 cases published to date.

In this article, we report 2 cases of PPIH associated with the use of pantoprazole. Both patients presented with severe hypomagnesaemia and hypocalcaemia. One of them had associated hypokalemia and cardiac arrhythmia. A casual relation with PPIs postulated and supported by resolution of electrolyte abnormalities after discontinuation of PPIs.

Learning Physiology From Inherited Kidney Disorders

The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.

Proton-pump Inhibitor-induced Severe Hypomagnesemia and Hypocalcemia are Clinically Masked by Thiazide Diuretic

Hypomagnesemia, a side effect of proton-pump inhibitors (PPIs), can be asymptomatic. The presence of hypocalcemia or hypokalemia is indicative of hypomagnesemia; however, the concomitant use of PPIs and thiazide may mask hypocalcemia. A 79-year-old woman with a history of chronic heart failure and chronic kidney disease developed symptomatic hypocalcemia and hypomagnesemia. Five weeks earlier, she had developed thiazide-induced hyponatremia, so thiazide had been discontinued. Reviewing the patient's charts revealed that three discontinued thiazide administrations in the clinical course had unmasked hypocalcemia. Our case demonstrates that thiazide-induced hypercalcemia can be so prominent as to mask PPI-induced hypocalcemia and hypomagnesemia.

Clinical Approach to Hypocalcemia in Newborn Period and Infancy: Who Should Be Treated?

Introduction

Hypocalcemia is a common metabolic problem in newborn period and infancy. There is consensus on the treatment of the symptomatic cases while the calcium level at which the treatment will be initiated and the treatment options are still controversial in asymptomatic hypocalcemia.

Methods

This review article will cover hypocalcemia with specific reference to calcium homeostasis and definition, etiology, diagnosis, and treatment of hypocalcemia in newborn and infancy period.

Results

Hypocalcemia is defined as total serum calcium <8 mg/dL (2 mmol/L) or ionized calcium <4.4 mg/dL (1.1 mmol/L) for term infants or preterm infants weighing >1500 g at birth and total serum calcium <7 mg/dL (1.75 mmol/L) or ionized calcium <4 mg/dL (1 mmol/L) for very low birth weight infants weighing <1500 g. Early-onset hypocalcemia is generally asymptomatic; therefore, screening for hypocalcemia at the 24th and 48th hour after birth is warranted for infants with high risk of developing hypocalcemia. Late-onset hypocalcemia, which is generally symptomatic, develops after the first 72 h and toward the end of the first week of life. Excessive phosphate intake, hypomagnesemia, hypoparathyroidism, and vitamin D deficiency are commonest causes of late-onset hypocalcemia. Hypocalcemia should be treated according to etiology. Calcium replacement is the cornerstone of the treatment. Elementary calcium replacement of 40 to 80 mg/kg/d is recommended for asymptomatic newborns. Elementary calcium of 10 to 20 mg/kg (1–2 mL/kg/dose 10% calcium gluconate) is given as a slow intravenous infusion in the acute treatment of hypocalcemia in patients with symptoms of tetany or hypocalcemic convulsion.

Conclusion

Since most infants with hypocalcemia are usually asymptomatic, serum total or ionized calcium levels must be monitored in preterm infants with a gestational age <32 weeks, small for gestational age infants, infants of diabetic mothers, and infants with severe prenatal asphyxia with a 1 min Apgar score of <4. The treatment of hypocalcemia should be initiated immediately in infants with reduced calcium levels while investigating the etiology.

Infant of diabetic mother: what one needs to know?

The global incidence of diabetes mellitus, including diabetes in pregnant women, is on the rise. Diabetes mellitus in a pregnant woman jeopardizes not only maternal health but can also have significant implications on the child to be born. Therefore, timely diagnosis and strict glycemic control are of utmost importance in achieving a safe outcome for both the mother and fetus. The treating physician should be aware of the complications that can arise due to poor glycemic control during pregnancy. The objective of this article is to discuss the key concerns in a neonate born to diabetic mother, the underlying pathogenesis, and the screening schedule during pregnancy.

Hypomagnesemia in critically ill patients

BACKGROUND

Magnesium (Mg) is essential for life and plays a crucial role in several biochemical and physiological processes in the human body. Hypomagnesemia is common in all hospitalized patients, especially in critically ill patients with coexisting electrolyte abnormalities. Hypomagnesemia may cause severe and potential fatal complications if not timely diagnosed and properly treated, and associate with increased mortality.

MAIN BODY

Mg deficiency in critically ill patients is mainly caused by gastrointestinal and/or renal disorders and may lead to secondary hypokalemia and hypocalcemia, and severe neuromuscular and cardiovascular clinical manifestations. Because of the physical distribution of Mg, there are no readily or easy methods to assess Mg status. However, serum Mg and the Mg tolerance test are most widely used. There are limited studies to guide intermittent therapy of Mg deficiency in critically ill patients, but some empirical guidelines exist. Further clinical trials and critical evaluation of empiric Mg replacement strategies is needed.

CONCLUSION

Patients at risk of Mg deficiency, with typical biochemical findings or clinical symptoms of hypomagnesemia, should be considered for treatment even with serum Mg within the normal range.

Multiple Electrolyte and Metabolic Emergencies in a Single Patient

While some electrolyte disturbances are immediately life-threatening and must be emergently treated, others may be delayed without immediate adverse consequences. We discuss a patient with alcoholism and diabetes mellitus type 2 who presented with volume depletion and multiple life-threatening electrolyte and metabolic derangements including severe hyponatremia (serum sodium concentration [S_Na] 107 mEq/L), hypophosphatemia ("undetectable," <1.0 mg/dL), and hypokalemia (2.2 mEq/L), moderate diabetic ketoacidosis ([DKA], pH 7.21, serum anion gap [S_AG] 37) and hypocalcemia (ionized calcium 4.0 mg/dL), mild hypomagnesemia (1.6 mg/dL), and electrocardiogram with prolonged QTc. Following two liters of normal saline and associated increase in S_Na by 4 mEq/L and serum osmolality by 2.4 mosm/Kg, renal service was consulted. We were challenged with minimizing the correction of S_Na (or effective serum osmolality) to avoid the osmotic demyelinating syndrome while replacing volume, potassium, phosphorus, calcium, and magnesium and concurrently treating DKA. Our management plan was further complicated by an episode of significant aquaresis. A stepwise approach was strategized to prioritize and correct all disturbances with considerations that the treatment of one condition could affect or directly worsen another. The current case demonstrates that a thorough understanding of electrolyte physiology is required in managing complex electrolyte disturbances to avoid disastrous outcomes.

Suppression of Parathyroid Hormone in a Patient with Severe Magnesium Depletion

Hypomagnesemia is often associated with coexisting electrolyte abnormalities like hypokalemia and hypocalcemia. Hypocalcemia has been shown to be secondary to hypoparathyroidism induced by hypomagnesemia. Here, we discuss a case of a patient with severe hypomagnesemia and associated hypocalcemia. A 38-year-old lady was admitted to the hospital for weakness of lower extremities and an eventual fall. The exam was significant for decreased motor strength and some paresthesias. The laboratory data was significant for hypomagnesemia, hypokalemia, and low parathyroid level in the face of hypocalcemia. After replacing magnesium, the parathyroid hormone levels normalized and led to eventual correction of calcium levels without any additional calcium replacement therapy. There was complete symptom resolution with correction of electrolyte abnormalities. This case highlights the importance of looking for all associated abnormalities in a patient with hypomagnesemia and starting the replacement therapy by first replacing the magnesium and then the others as needed. Replacing the magnesium alone may correct the hypoparathyroidism and eliminate the need for calcium replacement.

Hypomagnesemia due to two novel TRPM6 mutations

BACKGROUND

Although most hypocalcemia with hypomagenesemia in the neonatal period is due to transient neonatal hypoparathyroidism, magnesium channel defects should also be considered.

CASE

We report a case of persistent hypomagnesemia in an 8-day-old Hispanic male who presented with generalized seizures. He was initially found to have hypomagnesemia, hypocalcemia, hyperphosphatemia and normal parathyroid hormone. Serum calcium normalized with administration of calcitriol and calcium carbonate. Serum magnesium improved with oral magnesium sulfate. However, 1 week after magnesium was discontinued, serum magnesium declined to 0.5 mg/dL. Magnesium supplementation was immediately restarted, and periodic seizure activity resolved after serum magnesium concentration was maintained above 0.9 mg/dL. The child was eventually weaned off oral calcium and calcitriol with persistent normocalemia. However, supraphysiologic oral magnesium doses were necessary to prevent seizures and maintain serum magnesium at the low limit of normal.

METHODS AND RESULTS

As his clinical presentation suggested primary renal magnesium wastage, TRPM6 gene mutations were suspected; subsequent genetic testing revealed the child to be compound heterozygous for TRPM6 mutations.

CONCLUSION

Two novel TRPM6 mutations are described with a new geographic and ethnic origin. This case highlights the importance of recognizing disorders of magnesium imbalance and describing new genetic mutations.

Magnesium physiology and clinical therapy in veterinary critical care

OBJECTIVE

To review magnesium physiology including absorption, excretion, and function within the body, causes of magnesium abnormalities, and the current applications of magnesium monitoring and therapy in people and animals.

ETIOLOGY

Magnesium plays a pivotal role in energy production and specific functions in every cell in the body. Disorders of magnesium can be correlated with severity of disease, length of hospital stay, and recovery of the septic patient. Hypermagnesemia is seen infrequently in people and animals with significant consequences reported. Hypomagnesemia is more common in critically ill people and animals, and can be associated with platelet, immune system, neurological, and cardiovascular dysfunction as well as alterations in insulin responsiveness and electrolyte imbalance.

DIAGNOSIS

Measurement of serum ionized magnesium in critically or chronically ill veterinary patients is practical and provides information necessary for stabilization and treatment. Tissue magnesium concentrations may be assessed using nuclear magnetic resonance spectroscopy as well as through the application of fluorescent dye techniques.

THERAPY

Magnesium infusions may play a therapeutic role in reperfusion injury, myocardial ischemia, cerebral infarcts, systemic inflammatory response syndromes, tetanus, digitalis toxicity, bronchospasms, hypercoagulable states, and as an adjunct to specific anesthetic or analgesic protocols. Further veterinary studies are needed to establish the frequency and importance of magnesium disorders in animals and the potential benefit of magnesium infusions as a therapeutic adjunct to specific diseases.

PROGNOSIS

The prognosis for most patients with magnesium disorders is variable and largely dependent on the underlying cause of the disorder.

Magnesium intake, bone mineral density, and fractures: results from the Women's Health Initiative Observational Study

BACKGROUND

Magnesium is a necessary component of bone, but its relation to osteoporotic fractures is unclear.

OBJECTIVE

We examined magnesium intake as a risk factor for osteoporotic fractures and altered bone mineral density (BMD).

DESIGN

This prospective cohort study included 73,684 postmenopausal women enrolled in the Women's Health Initiative Observational Study. Total daily magnesium intake was estimated from baseline food-frequency questionnaires plus supplements. Hip fractures were confirmed by a medical record review; other fractures were identified by self-report. A baseline BMD analysis was performed in 4778 participants.

RESULTS

Baseline hip BMD was 3% higher (P < 0.001), and whole-body BMD was 2% higher (P < 0.001), in women who consumed >422.5 compared with <206.5 mg Mg/d. However, the incidence and RR of hip and total fractures did not differ across quintiles of magnesium. In contrast, risk of lower-arm or wrist fractures increased with higher magnesium intake [multivariate-adjusted HRs of 1.15 (95% CI: 1.01, 1.32) and 1.23 (95% CI: 1.07, 1.42) for quintiles 4 and 5, respectively, compared with quintile 1; P-trend = 0.002]. In addition, women with the highest magnesium intakes were more physically active and at increased risk of falls [HR for quintile 4: 1.11 (95% CI: 1.06, 1.16); HR for quintile 5: 1.15 (95% CI: 1.10, 1.20); P-trend < 0.001].

CONCLUSIONS

Lower magnesium intake is associated with lower BMD of the hip and whole body, but this result does not translate into increased risk of fractures. A magnesium consumption slightly greater than the Recommended Dietary Allowance is associated with increased lower-arm and wrist fractures that are possibly related to more physical activity and falls.

Hypomagnesemia and proton-pump inhibitors

INTRODUCTION

Proton pump inhibitors (PPIs) have been linked to clinically symptomatic hypomagnesemia.

AREAS COVERED

We searched Medline database in all languages using 'proton-pump inhibitors, magnesium, hypomagnesemia and hypomagnesemic hypoparathyroidism' as search terms and other articles were identified through searches of the files of the authors and reference lists from relevant articles. All patients presented with hypomagnesemic hypoparathyroidism, however, they rarely had life-threatening conditions such as malignant ventricular arrhythmias associated with prolonged QT interval, tetany and generalized seizures. Hypomagnesemia was seen with different PPIs, which could suggest a class effect, and was refractory to Mg replacement until PPIs were stopped. Hypomagnesemia may recur after re-challenge with the same or a different PPI and is not clearly dose-related. Mechanisms are poorly understood but PPI-induced hypochlorhydria does not seem involved. Carriers of TRPM6/7 mutations could be at risk.

EXPERT OPINION

Although mechanism and incidence rate remain unclear, there seems little doubt that PPIs may cause hypomagnesemia. We should obtain blood Mg levels prior to initiation of PPIs when patients are expected to be on treatment for long period of time and in those with other potential causes of hypomagnesemia. Use of H2-blockers may be an appropriate alternative.

Proton pump inhibitor-induced hypomagnesemia: A new challenge

Proton pump inhibitors (PPIs) are commonly used in clinical practice for the prevention and treatment of peptic ulcer, gastritis, esophagitis and gastroesophageal reflux. Hypomagnesemia has recently been recognized as a side effect of PPIs. Low magnesium levels may cause symptoms from several systems, some of which being potentially serious, such as tetany, seizures and arrhythmias. It seems that PPIs affect the gastrointestinal absorption of magnesium. Clinicians should be vigilant in order to timely consider and prevent or reverse hypomagnesemia in patients who take PPIs, especially if they are prone to this electrolyte disorder.

A patient on long-term proton pump inhibitors develops sudden seizures and encephalopathy: an unusual presentation of hypomagnesaemia

Objective. To present an unusual but known cause of hypomagnesaemia induced-hypocalcaemia in a chronic GORD patient with severe symptoms with a review of the current literature. Methods. Analysis of the clinical and laboratory findings of the patient and discussion of the multi-factorial nature of his disease and the underlying mechanisms. Results. Our patient described features of magnesium deficiency such as weakness, muscle twitches, and fits with clinical signs of hypocalcaemia: a carpal pedal spasm and paraesthesia. Preadmission blood results revealed low calcium and magnesium levels. He was admitted to ITU, when he presented with seizures and developed encephalopathy. The total vitamin D level was 52.4 nmol/L (>49.9). His U&Es and LFTs were within the normal range with the exception of potassium. He was on Omeprazole for his GORD. With omission of the PPI 1 day after admission and replacement therapy, his ion levels normalised. Conclusion. Hypomagnesaemia is often undiagnosed and is associated with multiple biochemical abnormalities. Treatment focus should be aimed at stopping the PPI and replacing the magnesium. Over use of PPIs is a problem in practice, with the FDA issuing a warning over long-term use. Continued monitoring and decision making on dose reduction/withdrawal is essential to avoid complications.

Acute-onset hypomagnesemia-induced hypocalcemia caused by the refractoriness of bones and renal tubules to parathyroid hormone

Chronic hypomagnesemia is closely associated with hypocalcemia, which is caused by impaired parathyroid hormone (PTH) secretion or the refractoriness of bone and renal tubules to PTH. The dominant mechanism of acute-onset, hypomagnesemia-induced hypocalcemia is currently unclear. An 83-year-old man who had undergone chemotherapy with carboplatin for prostate cancer suffered from acute diarrhea and finger paresthesia. Laboratory data confirmed hypocalcemia as well as hypomagnesemia. Urinary calcium levels were not measured. However, the urinary fractional excretion of Mg (FE(Mg)) was elevated. Despite elevated PTH levels, the renal tubular maximal reabsorption rate of phosphate to GFR (TmP/GFR) was elevated, and bone formation and resorption markers were suppressed. A magnesium loading test revealed a clear magnesium deficiency. After administration of magnesium, bone marker levels were increased, and TmP/GFR was reduced to normal levels, despite the persistent elevation of PTH. Serum calcium levels eventually increased to approximately the reference range. Clinical histories and these observations both suggest that when patients with hypomagnesemia-induced hypocalcemia rapidly lose magnesium through complications such as diarrhea, the primary cause may be the refractoriness of bone and renal tubules to PTH, rather than impaired PTH secretion.

Serum magnesium in recovering acute renal failure

We studied the manifestations of hypomagnesemia in 50 patients with acute renal failure who had been admitted in our hospital over a period of ten months. All patients with serum creatine ≥ 2 mg/dL and normal baseline levels of serum calcium, magnesium, and potassium as well as normal ECG were included in the study. Patients with multi-organ failure, drug-induced acute renal failure, obstructive uropathy, and alcohol addiction were excluded. The mean age of our study population was 40 ± 15 years, 37 of the patients were male and 13 were female. Hypomagnesemia was observed in 31 patients out of 50 during the recovery period of acute renal failure with symptomatic hypomagnesemia being seen in 23 patients. Serum magnesium levels on the day of admission and during the recovery phase were 2.11 ± 0.38 mg/dL and 1.64 ± 0.41 mg/dL respectively. Paresthesia, irritability, agitation, dysartharia, vertigo, and associated hypokalemia and hypocalcemia were noted in symptomatic hypomagnesemic patients. Treatment of hypomagnesaemia and hypokalemia ameliorated the symptoms. We conclude that these abnormalities produce clinically significant manifestations in recovery phase of acute renal failure and clinicians should pay attention to these.

Evolution of blood magnesium and phosphorus ion levels following thyroidectomy and correlation with total calcium values

CONTEXT AND OBJECTIVE

magnesium ion concentration is directly related and phosphorus ion concentration is inversely related to calcemia. The aim of this study was to evaluate the evolution of magnesium and phosphorus ion levels in patients undergoing thyroidectomy and correlate these with changes to calcium concentration.

DESIGN AND SETTING

prospective study at the Alpha Institute of Gastroenterology, Hospital das Clínicas, Universidade Federal de Minas Gerais.

METHODS

the study included 333 patients, of both genders and mean age 45 ± 15 years, who underwent thyroidectomy between 2000 and 2005. Total calcium, phosphorus and magnesium were measured in the blood preoperatively and 24 and 48 hours postoperatively. Ionic changes were evaluated according to the presence or absence of postoperative hypocalcemia.

RESULTS

there were statistically significant drops in blood phosphorus levels 24 and 48 hours after thyroidectomy, compared with preoperative values, in the patients without hypocalcemia. In the patients who developed hypocalcemia, there was a significant drop in plasma phosphorus on the first postoperative day and an increase (also statistically significant) on the second day, in relation to preoperative phosphorus levels. A significant drop in postoperative magnesium was also observed on the first and second days after thyroidectomy in the patients with hypocalcemia, in relation to preoperative levels. In the patients without hypocalcemia, the drop in magnesium was significant on the first day, but there was no difference on the second day.

CONCLUSION

despite the postoperative changes, neither magnesium nor phosphorus ion levels had any role in post-thyroidectomy calcemia.

Magnesium deficiency. Etiology and clinical spectrum

Magnesium deficiency may complicate many diseases. The causes include the following: inadequate intake during starvation or increased requirement during early childhood, pregnancy, or lactation; excessive losses of magnesium as a result of malabsorption from the gastrointestinal tract or from the kidneys during use of diuretics; and to a combination of the two, as in alcoholism. Most often the etiological factors have been operative for a month or more. Acute hypomagnesemia can occur without previous Mg deficiency after epinephrine, cold stress and stress of serious injury or extensive surgery. The clinical manifestations depend on the age of the patient and may begin insidiously or with dramatic suddenness, or there may be no overt symptoms or signs. The manifestations can be divided into the following categories: totally non-specific symptoms and signs ascribable to the primary disease; neuromuscular hyperactivity including tremor, myoclonic jerks, convulsions, Chvostek sign, Trousseau sign (rarely), spontaneous carpopedal spasm (rarely), ataxia, nystagmus and dysphagia; psychiatric disturbances from apathy and coma to some of all facets of delirium; cardiac arrhythmias including ventricular fibrillation and sudden death; hypocalcemia which is responsive only to Mg therapy; and hypokalemia which is not easily nor completely corrected without Mg therapy. The diversity of etiologies and the multiplicity of manifestations result in confusion and controversy. The documentation of normal renal function is absolutely necessary for maximum doses. The order of magnitude of dose is 1.0 meq Mg/kg on day 1, and 0.3 to 0.5 mEq/kg per day for 3 to 5 days. In emergencies such as convulsions or ventricular arrhythmias, a bolus injection of 1.0 gm (8.1 meq) of MgSO4 is indicated. Therapy of Mg deficiency in the presence of renal insufficiency requires smaller doses and frequent monitoring. Complete repletion occurs slowly.

Clinical consequences and management of hypomagnesemia

Magnesium deficiency and hypomagnesemia remain quite prevalent, particularly in patients in intensive care units, and may have important clinical consequences. Magnesium should be measured directly in clinical circumstances in which a risk for magnesium deficiency exists and appropriately corrected when found. This commentary reviews the current knowledge of magnesium homeostasis and the risk factors and clinical consequences of magnesium deficiency and outlines approaches to therapy.

Electrolyte disturbances in patients with hyponatremia

OBJECT

Electrolyte abnormalities are frequently observed in patients with hyponatremia. The aim of this study was to determine the incidence of various electrolyte abnormalities encountered in hyponatremic patients admitted to an internal medicine clinic, as well as to investigate the possible pathogenetic mechanisms responsible for these abnormalities.

PATIENTS AND METHODS

We prospectively studied 204 adult patients who either on admission to our clinic or during their hospitalization were found to have hyponatremia.

RESULTS

Ninety-two patients (45.5%) had at least one additional electrolyte abnormality. Hypophosphatemia was the most frequent electrolyte disorder observed (35 patients, 17%). Hypokalemia was seen in 32 patients (15.8%), hypomagnesemia in 31 patients (15.2%) and hyperkalemia in 12 patients (5.9%). Moreover, 5 patients (2.5%) had hyperphosphatemia, 4 patients (1.9%) exhibited hypermagnesemia, 3 patients (1.4%) had hypercalcemia, and 6 patients (2.9%) had true hypocalcemia. There were no statistically significant differences regarding the incidence of these electrolyte abnormalities (as a whole) between the main subgroups of hyponatremic patients (diuretic-induced, syndrome of inappropriate antidiuretic hormone, hypovolemia-induced and edematous state-related). However, hypokalemia and hypomagnesemia were more frequently observed in patients with diuretic-induced hyponatremia, while hyperkalemia was more frequently seen in edematous state-related hyponatremia.

CONCLUSIONS

Additional electrolyte abnormalities are frequently encountered in patients with hyponatremia of any origin admitted to an internal medicine clinic.

Physiology of epithelial Ca2+ and Mg2+ transport

Ca2+ and Mg2+ are essential ions in a wide variety of cellular processes and form a major constituent of bone. It is, therefore, essential that the balance of these ions is strictly maintained. In the last decade, major breakthrough discoveries have vastly expanded our knowledge of the mechanisms underlying epithelial Ca2+ and Mg2+ transport. The genetic defects underlying various disorders with altered Ca2+ and/or Mg2+ handling have been determined. Recently, this yielded the molecular identification of TRPM6 as the gatekeeper of epithelial Mg2+ transport. Furthermore, expression cloning strategies have elucidated two novel members of the transient receptor potential family, TRPV5 and TRPV6, as pivotal ion channels determining transcellular Ca2+ transport. These two channels are regulated by a variety of factors, some historically strongly linked to Ca2+ homeostasis, others identified in a more serendipitous manner. Herein we review the processes of epithelial Ca2+ and Mg2+ transport, the molecular mechanisms involved, and the various forms of regulation.

Alterations in electrolyte equilibrium in patients with acute leukemia

BACKGROUND AND AIM

A wide array of disturbances in electrolyte equilibrium is commonly seen in patients with acute leukemia (AL). These abnormalities present a potential hazard in these patients, as that of enhancing the cardiotoxic effects of certain chemotherapeutic regimens. The literature dealing with AL-related electrolyte abnormalities and their interactions in leukemic patients was reviewed.

DATA SYNTHESIS

Sources included MEDLINE and EMBASE. The search strategy was based on the combination of 'acute leukemia', 'electrolyte abnormalities', 'acid-base disorders', 'potassium', 'sodium', 'magnesium', 'calcium', and 'phosphorus'. References of retrieved articles were also screened. A decrease in serum potassium, mainly owing to lysozyme-induced tubular damage, appears to be one of the most frequent and potentially hazardous abnormalities. Other clinically significant metabolic perturbations include hyponatremia and hypercalcemia.

CONCLUSION

A broad spectrum of electrolyte abnormalities is encountered in the clinical setting of AL, which are related to the disease process per se and/or to the therapeutic interventions. Clinicians should be vigilant for early detection and appropriate management of these disorders before the initiation of chemotherapy regimens as well as during treatment.

Insights into the molecular nature of magnesium homeostasis

Magnesium is an important cofactor for many biological processes, such as protein synthesis, nucleic acid stability, or neuromuscular excitability. Extracellular magnesium concentration is tightly regulated by the extent of intestinal absorption and renal excretion. Despite the critical role of magnesium handling, the exact mechanisms mediating transepithelial transport remained obscure. In the past few years, the genetic disclosure of inborn errors of magnesium handling revealed several new proteins along with already known molecules unexpectedly involved in renal epithelial magnesium transport, e.g., paracellin-1, a key player in paracellular magnesium and calcium reabsorption in the thick ascending limb or the gamma-subunit of the Na(+)-K(+)-ATPase in the distal convoluted tubule. In this review, we focus on TRPM6, an ion channel of the "transient receptor potential (TRP) gene family, which, when mutated, causes a combined defect of intestinal magnesium absorption and renal magnesium conservation as observed in primary hypomagnesemia with secondary hypocalcemia.

Genetics of hereditary disorders of magnesium homeostasis

Magnesium plays an essential role in many biochemical and physiological processes. Homeostasis of magnesium is tightly regulated and depends on the balance between intestinal absorption and renal excretion. During the last decades, various hereditary disorders of magnesium handling have been clinically characterized and genetic studies in affected individuals have led to the identification of some molecular components of cellular magnesium transport. In addition to these hereditary forms of magnesium deficiency, recent studies have revealed a high prevalence of latent hypomagnesemia in the general population. This finding is of special interest in view of the association between hypomagnesemia and common chronic diseases such as diabetes, coronary heart disease, hypertension, and asthma. However, valuable methods for the diagnosis of body and tissue magnesium deficiency are still lacking. This review focuses on clinical and genetic aspects of hereditary disorders of magnesium homeostasis. We will review primary defects of epithelial magnesium transport, disorders associated with defects in Ca(2+)/ Mg(2+) sensing, as well as diseases characterized by renal salt wasting and hypokalemic alkalosis, with special emphasis on disturbed magnesium homeostasis.

Magnesium and the parathyroid

The serum levels of parathyroid hormone and magnesium depend on each other in a complex manner. The secretion of parathyroid hormone by the parathyroid is physiologically controlled by the serum calcium level, but magnesium can exert similar effects. While low levels of magnesium stimulate parathyroid hormone secretion, very low serum concentrations induce a paradoxical block. This block leads to clinically relevant hypocalcemia in severely hypomagnesiemic patients. The mechanism of this effect has recently been traced to an activation of the alpha-subunits of heterotrimeric G-proteins. This activation mimicks activation of the calcium sensing receptor and thus causes inhibition of parathyroid hormone secretion. In addition to the effects of magnesium on parathyroid hormone secretion, parathyroid hormone in turn regulates magnesium homeostasis by modulating renal magnesium reabsorption. The distal convoluted tubule is of crucial importance for parathyroid hormone-regulated magnesium homeostasis.

Severe hypomagnesaemia-induced hypocalcaemia in a patient with Gitelman's syndrome

Gitelman's syndrome (GS) is characterized by hyperreninaemic hyperaldosteronism, hypokalaemia, metabolic alkalosis, hypomagnesaemia and hypocalciuria and is due to a defect of the Na-Cl cotransporter at the distal tubule, which may appear in a sporadic or in a familial form. It is an autosomal recessive disorder associated with normal or reduced blood pressure. We report a case of severe hypomagnesaemia-induced hypocalcaemia in a 39-year-old Caucasian woman with GS. The patient had impaired parathormone (PTH) responsiveness to peripheral stimuli, as proved by the marked PTH increase and normalization of plasma calcium levels after acute and chronic administration of magnesium salts. Secondary normotensive hyperreninaemic hyperaldosteronism with hypokalaemia and metabolic alkalosis was also present. Normal plasma renin activity (PRA) and aldosterone levels were restored by administration of an inhibitor of prostaglandin synthesis. The electrolyte imbalance was successfully corrected with chronic treatment with magnesium and potassium salts. Genetic analysis identified a compound heterozygous mutation in the Na-Cl cotransporter gene (NCCT), confirming the diagnosis of GS. The striking feature of this case of GS was impaired PTH responsiveness to peripheral stimuli determined by hypomagnesaemia and the resulting severe hypocalcaemia, which had not previously been described in this syndrome.

Secondary hypoparathyroidism attributed to hypomagnesemia in a dog with protein-losing enteropathy

Severe hypomagnesemia (0.8 mg/dl; reference range, 1.6 to 2.3 mg/dl), hypocalcemia, and protein-losing enteropathy were identified in a 5-year-old castrated male 3-kg (6.6 lb) Shih Tzu examined because of anorexia, lethargy, paresis, and abdominal distention. Histologic examination of intestinal biopsy specimens revealed lymphangiectasia and lymphocytic, plasmacytic, neutrophilic infiltrates. Initial treatment included administration of magnesium (0.80 mEq/kg [0.36 mEq/lb]) of body weight in a balanced electrolyte solution. This treatment resulted in normalization of the serum magnesium concentration (1.7 mg/dl); resolution of the lethargy, paresis, and tachycardia; and an increase in the serum parathyroid hormone and ionized calcium concentrations. Findings were consistent with secondary hypoparathyroidism attributable to hypomagnesemia. Magnesium concentration should be monitored in all dogs with gastrointestinal tract disease, especially those with protein-losing enteropathy, anorexia, and weakness.

Inherited primary renal tubular hypokalemic alkalosis: a review of Gitelman and Bartter syndromes

Inherited hypokalemic metabolic alkalosis, or Bartter syndrome, comprises several closely related disorders of renal tubular electrolyte transport. Recent advances in the field of molecular genetics have demonstrated that there are four genetically distinct abnormalities, which result from mutations in renal electrolyte transporters and channels. Neonatal Bartter syndrome affects neonates and is characterized by polyhydramnios, premature delivery, severe electrolyte derangements, growth retardation, and hypercalciuria leading to nephrocalcinosis. It may be caused by a mutation in the gene encoding the Na-K-2Cl cotransporter (NKCC2) or the outwardly rectifying potassium channel (ROMK), a regulator of NKCC2. Classic Bartter syndrome is due to a mutation in the gene encoding the chloride channel (CLCNKB), also a regulator of NKCC2, and typically presents in infancy or early childhood with failure to thrive. Nephrocalcinosis is typically absent despite hypercalciuria. The hypocalciuric, hypomagnesemic variant of Bartter syndrome (Gitelman syndrome), presents in early adulthood with predominantly musculoskeletal symptoms and is due to mutations in the gene encoding the Na-Cl cotransporter (NCCT). Even though our understanding of these disorders has been greatly advanced by these discoveries, the pathophysiology remains to be completely defined. Genotype-phenotype correlations among the four disorders are quite variable and continue to be studied. A comprehensive review of Bartter and Gitelman syndromes will be provided here.

Hypomagnesemia and hypocalcemia associated with protein-losing enteropathy in Yorkshire terriers: five cases (1992-1998)

OBJECTIVE

To determine clinical and laboratory findings associated with protein-losing enteropathy, hypomagnesemia, and hypocalcemia in Yorkshire Terriers.

DESIGN

Retrospective study.

ANIMALS

5 purebred or crossbred Yorkshire Terriers with protein-losing enteropathy, hypomagnesemia, and hypocalcemia.

PROCEDURE

Medical records were reviewed for dogs with protein-losing enteropathy, hypomagnesemia, and hypocalcemia.

RESULTS

Of 8 dogs with these signs, 5 had Yorkshire Terrier breeding. Common findings were diarrhea, abdominal effusion, leukocytosis, neutrophilia, hypocalcemia (ionized calcium), hypomagnesemia, hypoproteinemia, hypoalbuminemia, hypocholesterolemia, and increased serum activity of aspartate aminotransferase.

CONCLUSIONS AND CLINICAL RELEVANCE

Yorkshire Terriers are at increased risk for development of protein-losing enteropathy with hypomagnesemia and decreased ionized calcium concentration. Hypomagnesemia and hypocalcemia may have a related pathogenesis involving intestinal loss, malabsorption, and abnormalities of vitamin D and parathyroid hormone metabolism. Serum electrolyte replacement may be required to avoid neurologic and metabolic problems.

Acid-base and electrolyte abnormalities in patients with acute leukemia

Disturbances of acid-base balance and electrolyte abnormalities are commonly seen in patients with acute leukemia. Our study aimed at illuminating the probable pathogenetic mechanisms responsible for these disturbances in patients with acute leukemia admitted to our hospital. We studied 66 patients (24 men and 44 women) aged between 17 and 87 years old on their admission and prior to any therapeutic intervention. Patients with diabetes mellitus, acute or chronic renal failure, hepatic failure, patients receiving drugs that influence acid-base status and electrolyte parameters during the last month, such as corticosteroids, cisplatin, diuretics, antacids, aminoglycosides, amphotericin, penicillin, and K(+), PO(4)(3-), or Mg(2+) supplements were excluded. Forty-one patients had at least one acid-base or electrolyte disturbance. There were no significant differences in the incidence of acid-base balance and electrolyte abnormalities between patients with acute myeloid leukemia (AML) and patients with acute lymphoblastic leukemia (ALL). The most frequent electrolyte abnormality was hypokalemia, observed in 41 patients (63%), namely in 34 patients with AML, and 7 with ALL; the main underlying pathophysiologic mechanism was inappropriate kaliuresis. Furthermore, hypokalemic patients more frequently experienced concurrent electrolyte disturbances (i.e., hyponatremia, hypocalcemia, hypophosphatemia, and hypomagnesemia), as well as various acid-base abnormalities compared to normokalemic patients. Hypokalemia in patients with acute leukemia may serve as an indicator of multiple concurrent, interrelated electrolyte disturbances, especially in patients with AML.

Magnesium supplementation and osteoporosis

Among other things, magnesium regulates active calcium transport. As a result, there has been a growing interest in the role of magnesium (Mg) in bone metabolism. A group of menopausal women were given magnesium hydroxide to assess the effects of magnesium on bone density. At the end of the 2-year study, magnesium therapy appears to have prevented fractures and resulted in a significant increase in bone density.