Hypermagnesemia

Hypermagnesemia is defined as a serum magnesium level greater than 0.9 mmol/l, subject to the reference laboratory's specific standards. It is a rare electrolyte disorder and is usually asymptomatic or mildly symptomatic. Severe, life-threatening cases are exceptionally rare and typically occur in patients with (pre)-terminal renal failure or multisystem failure.

Clinical Presentation

Hypermagnesemia is rarely symptomatic.

However, the following manifestations may occasionally be observed: hypotension, hyporeflexia, muscle weakness, arrhythmias, altered consciousness up to coma, risk of cardio-respiratory arrest.

The clinical severity is proportional to the biological severity:

• If < 2 mmol/l: generally asymptomatic
• If 2 to 4 mmol/l: nausea, vomiting, paresthesia ++
• If > 4 mmol/l (severe): possible muscle disorders, altered consciousness, cardiac conduction disturbances
• If > 8 mmol/l: imminent risk of cardio-respiratory arrest

Etiologies

• Chronic renal failure (pre-terminal or on hemodialysis) ++++
• Hyperparathyroidism, hypothyroidism, Addison's disease, magnesium-containing antacids, lithium intoxication, metabolic acidosis, administration of magnesium sulfate, etc.

Additional Tests

• Electrocardiogram (ECG): possible peaked T waves, atrioventricular block (AVB)
• Blood work: urea, creatinine, complete electrolyte panel

Therapeutic Management - Treatments

• Discontinue magnesium intake and treat the underlying cause if possible
• In case of symptomatic hypermagnesemia:
  • 1 g of calcium gluconate or calcium chloride IV over 2 to 5 minutes, may be repeated after 5 to 10 minutes
    • Alternative: G5 infusion + insulin
  • Abundant IV fluids + furosemide
  • Consider hemodialysis if clinical deterioration occurs despite management or in cases of severe hypermagnesemia

Bibliography

EMC, Traité de néphrologie, Elsevier, 2018

Longo DL et al., Harrison - Principes de médecine interne, 18e éd., Lavoisier, 2013