What are the causes of hypomagnesemia and hypermagnesemia?

Causes of Hypomagnesemia and Hypermagnesemia

Hypomagnesemia and hypermagnesemia are electrolyte disorders with distinct etiologies, with hypomagnesemia being far more common and occurring in up to 12% of hospitalized patients and 60-65% of critically ill patients, while hypermagnesemia is relatively rare and primarily occurs in patients with renal insufficiency.

Causes of Hypomagnesemia (<0.70 mmol/L)

Gastrointestinal Causes

• Inadequate magnesium intake
• Malabsorption syndromes
• Diarrhea
• Chronic use of proton pump inhibitors 1

Renal Causes

• Kidney replacement therapy (KRT), especially continuous KRT (CKRT) 1
• Regional citrate anticoagulation during CKRT (magnesium is lost in the effluent as magnesium-citrate complexes) 1
• Diuretic therapy (especially loop diuretics) 1
• Genetic renal disorders causing magnesium wasting 2
• Drug-induced renal magnesium wasting:
  • Aminoglycosides
  • Amphotericin B
  • Cisplatin 3

Other Causes

• Hypercalcemia
• Volume expansion 1
• Redistribution from extracellular to intracellular space 2

Clinical Manifestations of Hypomagnesemia

• Asymptomatic (when mild)
• Neuromuscular symptoms (muscle irritability, clonic twitching, tremors) 4
• Cardiovascular manifestations (arrhythmias, especially ventricular arrhythmias) 2
• Often accompanied by hypocalcemia and hypokalemia 4

Causes of Hypermagnesemia (>2.2 mEq/L)

Primary Cause

• Renal insufficiency with decreased glomerular filtration rate 5, 6, 7

Contributing Factors

• Excessive magnesium intake or administration:
  • Magnesium-containing medications (antacids, laxatives, cathartics) 5, 6
  • Intravenous magnesium sulfate (especially in obstetric patients for preeclampsia/eclampsia) 5
  • Magnesium-containing supplements 5, 6
• Bowel obstruction in patients taking magnesium-containing medications 5
• Metabolic disorders increasing susceptibility to toxic effects 5

Classification and Clinical Manifestations of Hypermagnesemia

• Mild (2.2-2.5 mEq/L): Often asymptomatic or mild symptoms
• Moderate (2.5-5.0 mEq/L): Hyporeflexia, nausea, vomiting, facial flushing, lethargy
• Severe (>5.0 mEq/L): Complete loss of deep tendon reflexes, severe hypotension, respiratory depression, heart blocks, coma 5

Diagnostic Approach

• For hypomagnesemia: Measure fractional excretion of magnesium and urinary calcium-creatinine ratio
  • Fractional excretion <2%: Suggests gastrointestinal loss
  • Fractional excretion >2% with normal kidney function: Indicates renal magnesium wasting 2
• For hypermagnesemia: Confirm with serum magnesium levels and assess renal function 5

Prevention Strategies

• For hypomagnesemia during KRT: Use dialysis solutions containing magnesium 1
• For hypermagnesemia:
  • Regular monitoring of magnesium levels in high-risk patients
  • Avoid magnesium-containing medications in patients with renal insufficiency 5

Treatment Considerations

• Hypomagnesemia:
  • Asymptomatic patients: Oral magnesium supplements
  • Symptomatic patients with severe deficiency (<1.2 mg/dL): Parenteral magnesium 2
• Hypermagnesemia:
  • Discontinue magnesium-containing medications
  • Intravenous calcium (calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL) as physiological antagonist in severe cases
  • Hemodialysis for severe cases with inadequate response 5, 7

Understanding these causes and their management is crucial as both conditions can lead to significant morbidity and mortality if not properly identified and treated.