Symptoms of Hypomagnesemia
Low magnesium primarily causes neuromuscular irritability, cardiac arrhythmias, and associated electrolyte disturbances that can range from subtle symptoms like muscle twitching and fatigue to life-threatening cardiac events.
Neuromuscular Manifestations
The most prominent symptoms of hypomagnesemia involve neuromuscular hyperexcitability, which develops when serum magnesium falls below 1.5 mEq/L 1:
- Muscle irritability, clonic twitching, and tremors are early predominant deficiency effects that may develop within 3-4 days to weeks of magnesium depletion 2
- Muscular weakness and cramps occur as magnesium is essential for muscular contraction regulation 3, 4
- Loss of deep tendon reflexes occurs as magnesium levels rise (in hypermagnesemia), but hyperreflexia is characteristic of deficiency 1
- Tetany and seizures can occur in severe cases, as magnesium plays a critical role in stabilizing excitable membranes 1, 2
Cardiac Manifestations
The most life-threatening effect of hypomagnesemia is ventricular arrhythmia, particularly polymorphic ventricular tachycardia including torsades de pointes 1, 5:
- Cardiac arrhythmias develop because magnesium is necessary for cardiac excitability and the movement of sodium, potassium, and calcium into and out of cells 1, 3
- Prolonged QT interval on electrocardiogram may be present 1
- Increased sensitivity to digoxin occurs with concurrent hypomagnesemia 6
- Low plasma magnesium concentration is associated with poor prognosis in cardiac arrest patients 1
Associated Electrolyte Abnormalities
Hypomagnesemia frequently causes secondary electrolyte disturbances that produce their own symptoms 2, 6, 4:
- Hypocalcemia often follows low serum magnesium levels and may be refractory to treatment until magnesium is corrected 2, 6, 4
- Hypokalemia commonly accompanies magnesium deficiency and can be refractory to potassium replacement alone 6, 4
- These secondary abnormalities contribute to additional symptoms including mood swings, behavioral changes, and worsened cardiac instability 7
Neurological and Systemic Symptoms
Beyond acute neuromuscular effects, magnesium deficiency produces broader systemic manifestations 1, 2, 3, 7:
- Fatigue and irritability are common early symptoms 1
- Abnormal involuntary movements of any sort may occur 1
- Behavioral disorders can develop due to thiamine deactivation secondary to magnesium deficiency 7
- Confusion and altered mental status may be present in severe cases 1
Symptom Threshold and Detection
Most patients with hypomagnesemia are asymptomatic until the serum magnesium concentration falls below 1.2 mg/dL 4, 5. This creates a clinical pitfall: serum magnesium can be normal despite significant intracellular magnesium depletion 6, 4. The occurrence of a low serum level usually indicates significant magnesium deficiency 6.
Common Causes to Consider
Hypomagnesemia typically results from 1:
- Decreased absorption or increased gastrointestinal loss (diarrhea, malabsorption) 1
- Increased renal losses from diuretics (loop and thiazide), alcohol, certain medications (pentamidine, aminoglycosides, cisplatin) 1, 6
- Alterations in thyroid hormone function 1
- Malnourishment 1
Clinical Pitfall
Hypomagnesemia is frequently encountered in hospitalized patients and is seen most often in intensive care units, yet approximately 10% of patients admitted to city hospitals are hypomagnesemic and often go undetected 6, 4. The deficiency can present with such a wide range of symptoms—from muscle cramps to life-threatening arrhythmias—that it may be overlooked unless specifically considered 7, 6.