What are the symptoms and treatment of hypomagnesemia?

Hypomagnesemia: Symptoms and Treatment

Hypomagnesemia (serum magnesium <1.3 mEq/L) most critically presents with life-threatening polymorphic ventricular tachycardia including torsades de pointes, requiring immediate IV magnesium sulfate 1-2 g bolus, and commonly manifests with neuromuscular irritability, cardiac arrhythmias, and concurrent refractory hypokalemia and hypocalcemia. 1

Clinical Presentation

Cardiovascular Manifestations (Most Critical)

• Polymorphic ventricular tachycardia, specifically torsades de pointes, represents the most life-threatening cardiac manifestation and can progress to pulseless cardiac arrest 1
• Cardiac arrhythmias of various types, with increased sensitivity to digoxin toxicity 2
• ECG changes including QT interval prolongation 1
• Low plasma magnesium concentration is associated with poor prognosis in cardiac arrest patients 1

Neuromuscular Symptoms

• Tetany similar to hypocalcemia despite normal or elevated serum calcium levels (4.3-5.3 mEq/L) 3
• Positive Chvostek and Trousseau signs 4
• Muscle irritability, clonic twitching, and tremors 3, 2
• Paresthesias 4
• Seizures (non-hypocalcemic) 1
• Abnormal involuntary movements 1

Neuropsychiatric Manifestations

• Confusion and hallucinations 1
• Irritability 1
• Emotional irritability and fatigue 1
• Nystagmus 1

Associated Electrolyte Disturbances

• Refractory hypokalemia that fails to correct until magnesium is repleted 2
• Refractory hypocalcemia that fails to correct until magnesium is repleted 2
• These concurrent electrolyte abnormalities occur because magnesium is necessary for the movement of sodium, potassium, and calcium into and out of cells 1

Timing of Symptom Onset

• Most patients with hypomagnesemia are asymptomatic 5, 4
• Symptoms typically do not arise until serum magnesium falls below 1.2 mg/dL (0.5 mmol/L) 5, 4
• Early symptoms may develop as early as 3-4 days or within weeks of magnesium depletion 3

Common Etiologies

Gastrointestinal Losses

• Decreased absorption or increased loss from intestines, particularly diarrhea 1
• Malabsorption and steatorrhea 2
• Protein-calorie malnutrition 2

Renal Losses

• Loop diuretics and thiazide diuretics (most common medication cause) 1, 2
• Aminoglycosides, cisplatin, pentamidine 1, 2
• Alcohol use 1, 2

Metabolic Conditions

• Diabetes mellitus (combination of factors) 2
• Alterations in thyroid hormone function 1

Treatment Algorithm

For Severe/Symptomatic Hypomagnesemia (<1.2 mg/dL or 0.5 mmol/L)

Immediate IV Treatment:

• For cardiac arrest or severe cardiotoxicity with torsades de pointes: IV magnesium sulfate 1-2 g bolus IV push (Class I recommendation) 1
• For symptomatic hypomagnesemia without cardiac arrest: parenteral magnesium is indicated 5, 4
• Onset of anticonvulsant action is immediate with IV administration and lasts approximately 30 minutes 3
• Effective anticonvulsant serum levels range from 2.5-7.5 mEq/L 3

For Moderate Hypomagnesemia (0.5-0.7 mmol/L)

• Oral magnesium supplementation if deficient diet or malabsorption present 4
• Prolonged therapy may be necessary 4
• Magnesium-containing antacids in normal dosage may be effective, though clinical proof is limited 4

For Mild Asymptomatic Hypomagnesemia

• Oral magnesium supplements are appropriate 5
• Daily calcium and vitamin D supplementation recommended (particularly in specific populations like 22q11.2 deletion syndrome) 1

Critical Treatment Considerations

Renal Function Assessment

• Establish adequate renal function before administering any magnesium supplementation 5
• Magnesium is excreted solely by the kidneys at a rate proportional to plasma concentration and glomerular filtration 3
• In renal insufficiency, lower the magnesium dose 4

Concurrent Electrolyte Repletion

• Always check and correct magnesium before attempting to correct refractory hypokalemia or hypocalcemia 2
• Hypokalemia and hypocalcemia often follow low serum magnesium levels and cannot be corrected until magnesium is repleted 3, 2

Monitoring Parameters

• Measure fractional excretion of magnesium and urinary calcium-creatinine ratio to determine etiology 5
• Fractional excretion <2% indicates appropriate renal conservation (gastrointestinal losses) 5
• Fractional excretion >2% with normal kidney function indicates renal magnesium wasting 5

Common Pitfalls

• Failing to recognize that normal serum magnesium can exist despite significant intracellular magnesium depletion 2
• Missing hypomagnesemia because it is underdiagnosed—seen in 11% of general hospital population and up to 65% of severely ill patients 4
• Attempting to correct hypokalemia or hypocalcemia without first addressing concurrent hypomagnesemia 2
• Administering magnesium without first confirming adequate renal function 5
• Using oral antacids in patients with hypophosphatemia (contraindicated) 4