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:
Decreased Intake:
Malnutrition
Prolonged parenteral nutrition without adequate magnesium supplementation
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:
Serum Magnesium Measurement:
Total serum magnesium level < 1.7 mg/dL (0.70 mmol/L)
Ionized magnesium measurement (if available) for more accurate assessment
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)
Electrocardiogram (ECG):
Prolonged QT interval
ST segment depression
T wave flattening or inversion
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:
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
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
Treatment of Underlying Cause:
Address gastrointestinal disorders if present
Adjust medications that may be contributing to hypomagnesemia
Consider dietitian consultation for long-term management
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
What is the definition of hypomagnesemia in children?
Serum magnesium levels below 1.7 mg/dL (0.70 mmol/L)
What is the most common cause of hypomagnesemia in hospitalized children?
Gastrointestinal losses (diarrhea, malabsorption)
Which medication class commonly causes hypomagnesemia as a side effect?
Proton pump inhibitors
What is the primary source of magnesium in the diet?
Green leafy vegetables, nuts, and whole grains
Which genetic disorder is characterized by renal magnesium wasting?
Gitelman syndrome
What is the role of the TRPM6 channel in hypomagnesemia?
Mutations in TRPM6 cause hypomagnesemia with secondary hypocalcemia
Which electrolyte imbalances are commonly associated with hypomagnesemia?
Hypokalemia and hypocalcemia
What is the most serious cardiac complication of severe hypomagnesemia?
Ventricular arrhythmias
Which neuromuscular symptom is characteristic of moderate hypomagnesemia?
Tetany
What is the effect of hypomagnesemia on deep tendon reflexes?
Hyperreflexia
Which gastrointestinal condition can lead to chronic hypomagnesemia?
Celiac disease
What is the effect of severe hypomagnesemia on calcium homeostasis?
Functional hypoparathyroidism leading to hypocalcemia
Which medication used in chemotherapy can cause hypomagnesemia?
Cisplatin
What is the primary treatment for symptomatic hypomagnesemia?
Intravenous magnesium replacement
Which form of magnesium is commonly used for oral supplementation?
Magnesium oxide
What is the role of vitamin D in magnesium homeostasis?
Enhancing intestinal magnesium absorption
Which laboratory test is used to assess urinary magnesium excretion?
24-hour urine magnesium collection
What is the effect of hypomagnesemia on the QT interval in ECG?
Prolongation of the QT interval
Which endocrine disorder can cause hypomagnesemia due to increased urinary magnesium excretion?
Hyperaldosteronism
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
Which genetic disorder is characterized by hypomagnesemia and hypercalciuria?
Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC)
What is the effect of hypomagnesemia on vitamin D metabolism?
Impaired conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D
Which medication used in the treatment of asthma can cause hypomagnesemia?
Beta-2 agonists (e.g., albuterol)
What is the role of magnesium in glucose metabolism?
Magnesium is a cofactor for enzymes involved in glucose metabolism and insulin action
Which condition can cause transient hypomagnesemia in newborns?
Transient neonatal hypoparathyroidism
What is the effect of hypomagnesemia on neuromuscular junction transmission?
Increased acetylcholine release leading to muscle hyperexcitability
Which imaging technique is used to assess for nephrocalcinosis in chronic hypomagnesemia?
Renal ultrasound
What is the role of magnesium in bone metabolism?
Magnesium is essential for bone mineralization and osteoblast function
Which medication used in the treatment of ADHD can cause hypomagnesemia?
Amphetamines
What is the effect of hypomagnesemia on parathyroid hormone secretion?
Impaired parathyroid hormone secretion and action