Hypomagnesaemia
Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management
Definition
Hypomagnesaemia is a serum magnesium level below the normal reference range (typically <0.75 mmol/L), which can lead to neuromuscular, cardiovascular, and metabolic disturbances.
Aetiology
- Gastrointestinal losses: chronic diarrhoea, malabsorption (e.g., coeliac disease, Crohn’s disease), excessive laxative use.
- Renal losses: diuretic use (loop and thiazide diuretics), tubular disorders, hyperaldosteronism.
- Alcoholism: associated with poor intake, diarrhoea, and renal losses.
- Endocrine disorders: hyperparathyroidism, diabetic ketoacidosis (DKA), hyperthyroidism.
- Medications: proton pump inhibitors (PPIs), aminoglycosides, cisplatin.
Pathophysiology
- Magnesium plays a crucial role in neuromuscular function, enzyme activity, and electrolyte balance.
- Deficiency affects potassium and calcium homeostasis, contributing to hypokalaemia and hypocalcaemia.
- Severe hypomagnesaemia can lead to cardiac arrhythmias, neuromuscular excitability, and seizures.
Risk Factors
- Chronic gastrointestinal disease.
- Use of diuretics or PPIs.
- Chronic alcohol use.
- Uncontrolled diabetes mellitus.
- Renal disorders affecting magnesium reabsorption.
Signs and Symptoms
- Neuromuscular: muscle cramps, tremors, tetany, seizures.
- Cardiovascular: arrhythmias (torsades de pointes), prolonged QT interval.
- Electrolyte disturbances: concurrent hypocalcaemia and hypokalaemia.
- Neuropsychiatric: lethargy, confusion, depression.
Investigations
- Serum magnesium: low levels confirm diagnosis.
- Serum calcium and potassium: assess for concurrent electrolyte disturbances.
- Renal function tests: assess for renal magnesium loss.
- ECG: check for QT prolongation and arrhythmias.
- Urinary magnesium excretion: differentiates between renal and gastrointestinal causes.
Management
1. Treat Underlying Cause:
- Discontinue offending drugs: stop PPIs or diuretics if possible.
- Correct gastrointestinal losses: manage chronic diarrhoea or malabsorption.
2. Magnesium Replacement:
- Oral magnesium supplements: preferred for mild cases (e.g., magnesium citrate, magnesium oxide).
- IV magnesium sulfate: indicated for severe cases or symptomatic hypomagnesaemia (e.g., arrhythmias, seizures).
3. Monitoring:
- Repeat magnesium levels to ensure adequate correction.
- Monitor ECG in severe cases.
4. Referral:
- Endocrinology: if associated with endocrine disorders or refractory cases.
- Nephrology: if due to renal magnesium wasting or chronic kidney disease.
- Cardiology: if presenting with arrhythmias requiring intervention.