What are the symptoms of hypomagnesemia?

Symptoms of Hypomagnesemia

Hypomagnesemia causes a spectrum of symptoms ranging from subtle neuromuscular irritability to life-threatening cardiac arrhythmias, with most patients remaining asymptomatic until serum magnesium falls below 1.2 mg/dL. 1, 2, 3

Neuromuscular Manifestations

The neuromuscular system is particularly sensitive to magnesium deficiency due to magnesium's critical role in stabilizing excitable membranes:

• Muscle irritability, clonic twitching, and tremors are predominant early deficiency effects that may develop within 3-4 days to weeks of magnesium depletion 2
• Hyperreflexia is characteristic of deficiency, representing increased deep tendon reflexes (in contrast, loss of reflexes occurs with magnesium excess) 1
• Tetany and seizures can occur in severe cases, as magnesium stabilizes neuronal membranes and prevents excessive excitability 1, 4
• Abnormal involuntary movements of any type may manifest 1
• Muscle weakness and numbness are common complaints 4

Cardiac Manifestations

The cardiovascular effects represent the most dangerous complications:

• Polymorphic ventricular tachycardia, particularly torsades de pointes, is the most life-threatening effect and can occur regardless of baseline magnesium level 1, 3, 5
• Prolonged QT interval on electrocardiogram is a hallmark finding 1, 6
• ST-segment depression and myocardial injury may occur, as demonstrated in cases presenting as type 2 myocardial infarction 6
• Elevated troponin levels can accompany severe deficiency 6
• Poor prognosis in cardiac arrest patients is associated with low plasma magnesium concentration 1

The cardiac arrhythmias develop because magnesium is essential for cardiac excitability and the movement of sodium, potassium, and calcium across cell membranes 1

Neurological and Systemic Symptoms

Central nervous system effects become prominent as deficiency worsens:

• Fatigue and irritability are common early symptoms 1
• Confusion, altered mental status, and delirium may present in severe cases, particularly in elderly patients 1, 6
• Lethargy, ataxia, and progression to coma can occur with profound deficiency 4

Associated Electrolyte Disturbances

A critical pitfall is that hypomagnesemia rarely occurs in isolation:

• Hypocalcemia often follows low serum magnesium levels and will be refractory to calcium supplementation until magnesium is corrected 1, 2
• Hypokalemia frequently accompanies magnesium deficiency because hypomagnesemia causes dysfunction of potassium transport systems and increases renal potassium excretion, making potassium replacement ineffective until magnesium is normalized 1, 2

Symptom Threshold

Most patients remain asymptomatic until serum magnesium concentration falls below 1.2 mg/dL (< 0.5 mmol/L), though symptoms can develop with levels less than 1.8 mg/dL (< 0.74 mmol/L). 2, 3 This explains why routine screening may miss clinically significant deficiency in high-risk populations.

Common Clinical Contexts

Recognize hypomagnesemia in these high-risk scenarios:

• Gastrointestinal losses from diarrhea, malabsorption, or high-output ileostomy 1, 4, 6
• Renal losses from loop or thiazide diuretics, aminoglycosides, cisplatin, amphotericin B, or pentamidine 1, 7
• Alcohol use disorder 1
• Malnourishment 1