Hypomagnesaemia

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | Example Management | References

Definition

Hypomagnesaemia refers to a lower-than-normal level of magnesium in the blood. Magnesium is a vital mineral involved in numerous physiological processes, including muscle and nerve function, blood glucose control, and protein synthesis.

Aetiology

Causes of hypomagnesaemia can include:

• Inadequate Intake: Poor dietary intake, malnutrition, or alcoholism.
• Increased Losses: Gastrointestinal losses (e.g., diarrhoea, vomiting), renal losses (e.g., diuretics, chronic kidney disease), or endocrine disorders (e.g., hyperaldosteronism).
• Reduced Absorption: Malabsorption syndromes (e.g., Crohn's disease, coeliac disease) or post-surgical changes (e.g., bariatric surgery).
• Medications: Use of proton pump inhibitors (PPIs), aminoglycosides, or chemotherapy agents.

Pathophysiology

Magnesium is crucial for numerous cellular processes, including ATP production, enzyme function, and stabilisation of cell membranes. Hypomagnesaemia can disrupt these processes, leading to:

• Impaired neuromuscular function
• Electrolyte imbalances (e.g., hypokalaemia, hypocalcaemia)
• Cardiac arrhythmias
• Increased neuromuscular excitability (e.g., tetany, seizures)

Risk Factors

• Chronic gastrointestinal disorders (e.g., Crohn's disease, chronic diarrhoea)
• Renal disorders (e.g., chronic kidney disease, use of diuretics)
• Endocrine disorders (e.g., diabetes mellitus, hyperaldosteronism)
• Alcoholism
• Older age
• Use of certain medications (e.g., PPIs, aminoglycosides)

Signs and Symptoms

Symptoms of hypomagnesaemia can vary in severity:

• Neuromuscular: Muscle cramps, tremors, weakness, tetany, seizures
• Cardiovascular: Palpitations, arrhythmias, hypertension
• Neurological: Confusion, apathy, depression, agitation
• Gastrointestinal: Nausea, vomiting, anorexia

Investigations

• Serum magnesium level: To confirm hypomagnesaemia
• Serum calcium and potassium levels: To assess for associated electrolyte imbalances
• Renal function tests: To evaluate kidney function
• Electrocardiogram (ECG): To detect any cardiac arrhythmias
• Gastrointestinal investigations: If malabsorption or chronic diarrhoea is suspected

Management

Primary Care Management

• Oral magnesium supplementation: For mild cases, magnesium oxide or magnesium citrate can be used.
• Dietary advice: Encourage consumption of magnesium-rich foods such as leafy green vegetables, nuts, seeds, whole grains, and fish.
• Education: Inform patients about the importance of magnesium in their diet and the potential side effects of medications that can cause magnesium depletion.
• Monitoring: Regular follow-up with serum magnesium levels to ensure adequate repletion.
• Referral: To a specialist if there is no response to oral supplementation, if there are severe symptoms, or if an underlying cause requires further investigation.

Specialist Management

• Intravenous magnesium: For severe hypomagnesaemia or symptomatic patients, magnesium sulphate is administered intravenously.
• Treat underlying cause: Address any contributing factors such as discontinuing causative medications, treating gastrointestinal disorders, or managing renal conditions.
• Correction of associated electrolyte imbalances: Potassium and calcium levels should be monitored and corrected if necessary.
• Hospital admission: For patients with severe symptoms or complications such as cardiac arrhythmias or seizures.
• Monitoring: Continuous cardiac monitoring for patients receiving IV magnesium, particularly if they have pre-existing cardiac conditions.

Example Management for Hypomagnesaemia

A patient presenting with muscle cramps and palpitations is found to have hypomagnesaemia. Initial management involves oral magnesium supplementation with magnesium oxide. The patient is advised to increase dietary intake of magnesium-rich foods. Regular follow-up is arranged to monitor serum magnesium levels and assess the response to treatment. If the patient does not respond to oral supplementation or if symptoms worsen, referral to a specialist for intravenous magnesium therapy and further investigation of underlying causes is warranted.

References

1. NICE. (2024). Intravenous Fluid Therapy in Adults in Hospital. Retrieved from NICE
2. NHS. (2023). Hypomagnesaemia. Retrieved from NHS
3. British Medical Journal (BMJ). (2022). Hypomagnesaemia: Diagnosis and Management. Retrieved from BMJ
4. World Health Organization (WHO). (2021). Clinical Management of Severe Hypomagnesaemia. Retrieved from WHO

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