Hypomagnesemia in Children

Hypomagnesemia in Children Introduction Etiology Clinical Presentation Diagnosis Management Complications

Introduction to Hypomagnesemia in Children

Hypomagnesemia is defined as a serum magnesium level below 1.7 mg/dL (0.70 mmol/L) in children. It is a relatively common electrolyte disorder in pediatric patients, particularly in critically ill children and those with certain chronic conditions. The normal range of serum magnesium in children varies slightly by age:

• Newborns: 1.5-2.3 mg/dL (0.62-0.95 mmol/L)
• Children: 1.7-2.3 mg/dL (0.70-0.95 mmol/L)
• Adults: 1.8-2.3 mg/dL (0.74-0.95 mmol/L)

Magnesium is crucial for numerous physiological processes, including neuromuscular function, enzyme activity, and energy metabolism. Recognizing and treating hypomagnesemia is essential in pediatric care to prevent potentially serious complications.

Etiology of Hypomagnesemia in Children

Hypomagnesemia in children can result from various mechanisms, including decreased intake, increased losses, or impaired absorption. The main causes include:

1. Decreased Intake:
   • Malnutrition
   • Prolonged parenteral nutrition without adequate magnesium supplementation
2. Gastrointestinal Losses:
   • Chronic diarrhea
   • Malabsorption syndromes (e.g., celiac disease, inflammatory bowel disease)
   • Short bowel syndrome
   • Pancreatic insufficiency
3. Renal Losses:
   • Tubulopathies (e.g., Gitelman syndrome, Bartter syndrome)
   • Nephrotoxic medications (e.g., aminoglycosides, amphotericin B, cisplatin)
   • Diuretic therapy (loop and thiazide diuretics)
   • Polyuric phase of acute tubular necrosis
4. Endocrine Disorders:
   • Hyperaldosteronism
   • Hyperthyroidism
   • Diabetes mellitus
5. Genetic Disorders:
   • Primary hypomagnesemia with secondary hypocalcemia
   • Familial hypomagnesemia with hypercalciuria and nephrocalcinosis
6. Other Causes:
   • Severe burns
   • Excessive sweating
   • Medication-induced (e.g., proton pump inhibitors, cyclosporine)
   • Refeeding syndrome

In neonates, maternal magnesium deficiency and certain intrauterine growth conditions can lead to hypomagnesemia.

Clinical Presentation of Hypomagnesemia in Children

The clinical manifestations of hypomagnesemia can be subtle and nonspecific, often overlapping with symptoms of hypocalcemia and hypokalemia. Symptoms typically appear when serum magnesium levels fall below 1.2 mg/dL (0.5 mmol/L). Common presentations include:

• Neuromuscular:
  • Tremors
  • Muscle cramps and spasms
  • Tetany
  • Seizures
  • Nystagmus
• Cardiovascular:
  • Arrhythmias (especially in association with hypokalemia)
  • Prolonged QT interval
  • Torsades de pointes
• Neuropsychiatric:
  • Irritability
  • Apathy
  • Depression
  • Confusion
• Metabolic:
  • Hypocalcemia (often refractory to calcium supplementation alone)
  • Hypokalemia
• Other:
  • Weakness and fatigue
  • Anorexia
  • Nausea and vomiting

In neonates, hypomagnesemia may present with poor feeding, lethargy, and increased jitteriness.

Diagnosis of Hypomagnesemia in Children

Diagnosis of hypomagnesemia involves both laboratory tests and clinical evaluation:

1. Serum Magnesium Measurement:
   • Total serum magnesium level < 1.7 mg/dL (0.70 mmol/L)
   • Ionized magnesium measurement (if available) for more accurate assessment
2. Other Laboratory Tests:
   • Serum calcium and potassium (often decreased in hypomagnesemia)
   • Renal function tests (BUN, creatinine)
   • Urinary magnesium excretion (to differentiate renal from non-renal losses)
   • Serum parathyroid hormone (may be low or inappropriately normal)
3. Electrocardiogram (ECG):
   • Prolonged QT interval
   • ST segment depression
   • T wave flattening or inversion
4. Clinical Evaluation:
   • Detailed history (including dietary habits, medication use, and chronic conditions)
   • Physical examination (focusing on neuromuscular and cardiovascular systems)
   • Assessment of Chvostek's and Trousseau's signs (may be positive)

It's important to consider hypomagnesemia in children with unexplained hypocalcemia, hypokalemia, or neuromuscular symptoms, especially those with risk factors or chronic conditions associated with magnesium deficiency.

Management of Hypomagnesemia in Children

The management of hypomagnesemia in children depends on the severity of symptoms and the underlying cause. Treatment strategies include:

1. Acute Symptomatic Hypomagnesemia:
   • Intravenous magnesium sulfate:
     • 25-50 mg/kg/dose (maximum 2 g) over 10-20 minutes
     • Can be repeated every 4-6 hours as needed
     • Continuous infusion of 30-50 mg/kg/day may be used in severe cases
2. Asymptomatic or Chronic Hypomagnesemia:
   • Oral magnesium supplements:
     • Magnesium oxide or magnesium chloride: 40-80 mg/kg/day divided into 3-4 doses
     • Magnesium gluconate: 50-100 mg/kg/day divided into 3-4 doses
3. Treatment of Underlying Cause:
   • Address gastrointestinal disorders if present
   • Adjust medications that may be contributing to hypomagnesemia
   • Manage endocrine disorders
4. Dietary Modifications:
   • Encourage magnesium-rich foods (e.g., leafy greens, nuts, whole grains)
   • Consider dietitian consultation for long-term management
5. Monitoring:
   • Serial serum magnesium levels
   • ECG monitoring during IV magnesium administration
   • Monitor for signs of magnesium toxicity (e.g., hypotension, respiratory depression)

In cases of severe hypomagnesemia with associated hypocalcemia and hypokalemia, all three electrolytes should be corrected simultaneously, with magnesium replacement being prioritized.

Complications of Hypomagnesemia in Children

Untreated or severe hypomagnesemia can lead to several serious complications:

• Cardiovascular Complications:
  • Cardiac arrhythmias (particularly in association with hypokalemia)
  • Increased risk of digoxin toxicity
  • Torsades de pointes
  • Increased risk of atherosclerosis (in chronic deficiency)
• Neuromuscular Complications:
  • Seizures
  • Tetany
  • Muscle weakness and cramps
• Metabolic Complications:
  • Refractory hypocalcemia
  • Hypokalemia
  • Metabolic acidosis
  • Impaired glucose tolerance
• Respiratory Complications:
  • Bronchial hyperreactivity
  • Increased risk of asthma exacerbations
• Growth and Development:
  • Impaired bone mineralization
  • Potential impact on growth in chronic deficiency
• Other Complications:
  • Increased inflammation and oxidative stress
  • Impaired immune function

Long-term complications of chronic hypomagnesemia may include an increased risk of osteoporosis, hypertension, and type 2 diabetes mellitus. Early recognition and treatment of hypomagnesemia are crucial to prevent these potential complications.

Hypomagnesemia in Children

1. What is the definition of hypomagnesemia in children?
   Serum magnesium levels below 1.7 mg/dL (0.70 mmol/L)
2. What is the most common cause of hypomagnesemia in hospitalized children?
   Gastrointestinal losses (diarrhea, malabsorption)
3. Which medication class commonly causes hypomagnesemia as a side effect?
   Proton pump inhibitors
4. What is the primary source of magnesium in the diet?
   Green leafy vegetables, nuts, and whole grains
5. Which genetic disorder is characterized by renal magnesium wasting?
   Gitelman syndrome
6. What is the role of the TRPM6 channel in hypomagnesemia?
   Mutations in TRPM6 cause hypomagnesemia with secondary hypocalcemia
7. Which electrolyte imbalances are commonly associated with hypomagnesemia?
   Hypokalemia and hypocalcemia
8. What is the most serious cardiac complication of severe hypomagnesemia?
   Ventricular arrhythmias
9. Which neuromuscular symptom is characteristic of moderate hypomagnesemia?
   Tetany
10. What is the effect of hypomagnesemia on deep tendon reflexes?
    Hyperreflexia
11. Which gastrointestinal condition can lead to chronic hypomagnesemia?
    Celiac disease
12. What is the effect of severe hypomagnesemia on calcium homeostasis?
    Functional hypoparathyroidism leading to hypocalcemia
13. Which medication used in chemotherapy can cause hypomagnesemia?
    Cisplatin
14. What is the primary treatment for symptomatic hypomagnesemia?
    Intravenous magnesium replacement
15. Which form of magnesium is commonly used for oral supplementation?
    Magnesium oxide
16. What is the role of vitamin D in magnesium homeostasis?
    Enhancing intestinal magnesium absorption
17. Which laboratory test is used to assess urinary magnesium excretion?
    24-hour urine magnesium collection
18. What is the effect of hypomagnesemia on the QT interval in ECG?
    Prolongation of the QT interval
19. Which endocrine disorder can cause hypomagnesemia due to increased urinary magnesium excretion?
    Hyperaldosteronism
20. What is the role of the calcium-sensing receptor (CaSR) in magnesium homeostasis?
    Regulating magnesium reabsorption in the thick ascending limb of the loop of Henle
21. Which genetic disorder is characterized by hypomagnesemia and hypercalciuria?
    Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC)
22. What is the effect of hypomagnesemia on vitamin D metabolism?
    Impaired conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D
23. Which medication used in the treatment of asthma can cause hypomagnesemia?
    Beta-2 agonists (e.g., albuterol)
24. What is the role of magnesium in glucose metabolism?
    Magnesium is a cofactor for enzymes involved in glucose metabolism and insulin action
25. Which condition can cause transient hypomagnesemia in newborns?
    Transient neonatal hypoparathyroidism
26. What is the effect of hypomagnesemia on neuromuscular junction transmission?
    Increased acetylcholine release leading to muscle hyperexcitability
27. Which imaging technique is used to assess for nephrocalcinosis in chronic hypomagnesemia?
    Renal ultrasound
28. What is the role of magnesium in bone metabolism?
    Magnesium is essential for bone mineralization and osteoblast function
29. Which medication used in the treatment of ADHD can cause hypomagnesemia?
    Amphetamines
30. What is the effect of hypomagnesemia on parathyroid hormone secretion?
    Impaired parathyroid hormone secretion and action

Further Reading

• Magnesium in Disease
• Disorders of Magnesium Metabolism: Hypomagnesemia and Hypermagnesemia
• UpToDate: Hypomagnesemia: Clinical manifestations of magnesium depletion
• Medscape: Hypomagnesemia