Symptoms and Risk Factors of Hypomagnesemia
Hypomagnesemia presents with a range of symptoms including seizures, abnormal involuntary movements, fatigue, emotional irritability, and potentially life-threatening cardiac arrhythmias such as torsades de pointes. 1
Clinical Presentation
Neurological Symptoms
- Seizures (particularly when associated with hypocalcemia)
- Abnormal involuntary movements
- Muscle irritability and clonic twitching
- Tremors
- Emotional irritability
- Confusion and hallucinations
- Nystagmus 2, 1, 3
Cardiovascular Symptoms
- Polymorphic ventricular tachycardia (torsades de pointes)
- Cardiac arrhythmias
- Electrocardiographic changes including prolonged QT interval 1, 3
Other Symptoms
- Fatigue and weakness
- Contractures and severe pain
- Hypokalemia and hypocalcemia (often follow low magnesium levels) 1, 3
Risk Factors
Medical Conditions
Medications
- Chemotherapy agents (particularly cisplatin and cetuximab) 2, 6
- Aminoglycoside antibiotics 7, 6
- Loop diuretics (inhibit sodium chloride transport in ascending loop of Henle) 8
- Thiazide diuretics (inhibit sodium chloride cotransporter in distal convoluted tubule) 8
- Amphotericin B 6
Gastrointestinal Causes
- Malnutrition or inadequate magnesium intake
- Increased gastrointestinal losses (diarrhea, vomiting)
- Malabsorption syndromes 8, 4
Renal Causes
- Increased renal magnesium wasting
- Genetic renal disorders (Bartter syndrome, Gitelman syndrome)
- Acquired renal disorders 8
Other Factors
- Alcohol consumption 2
- Consumption of carbonated beverages like colas 2
- Biological stress (surgery, childbirth, infection) 2
Diagnostic Approach
The diagnosis of hypomagnesemia is based on:
- Serum magnesium level less than 1.8 mg/dL (< 0.74 mmol/L) 8
- Symptoms typically appear when levels fall below 1.2 mg/dL 8
- Measurement of fractional excretion of magnesium and urinary calcium-creatinine ratio helps determine the cause 8
- Fractional excretion <2%: suggests gastrointestinal loss
- Fractional excretion >2% with normal kidney function: indicates renal magnesium wasting
Treatment Considerations
- Asymptomatic patients: Oral magnesium supplements 8
- Symptomatic patients with severe deficiency (<1.2 mg/dL): Parenteral magnesium 8
- For cardiotoxicity and cardiac arrest: IV magnesium 1-2 g of MgSO4 bolus (Class I recommendation) 2, 1
- For hypomagnesemia in cancer patients: Magnesium replacement is recommended (Level V, C) 2
Important Caveats
- Verify adequate renal function before administering magnesium supplementation 8
- Monitor for signs of magnesium toxicity (deep tendon reflexes decrease as plasma levels rise above 4 mEq/L and disappear at 10 mEq/L) 3
- Respiratory paralysis and heart block may occur at high plasma levels 3
- Serum magnesium concentrations exceeding 12 mEq/L may be fatal 3
- Hypomagnesemia often coexists with other electrolyte abnormalities (particularly hypokalemia and hypocalcemia) which may need concurrent management 3, 5