Internal Medicine

0521779407-14 CUNY1086/Karliner 0 521 77940 7 June 4, 2007 21:16

940 Magnesium Deficiency

MAGNESIUM DEFICIENCY

ELISABETH RYZEN, MD

history & physical

History

■Clinical deficiency occurs primarily due to renal or gut Mg wasting,

often coupled with inadequate intake

➣Causes include malabsorption syndromes, diarrhea, alcohol

abuse, protein-calorie malnutrition, diuretic therapy, diabetes

mellitus, cisplatin, aminoglycosides, amphotericin B, hypercal-

cemia, IV saline therapy, hungry bone syndrome

signs & symptoms

■Neurologic: weakness, tetany (+Chvostek’s or Trousseau’s), seizures,

fasciculations, psychiatric problems

■Cardiovascular: prolonged QT, ventricular arrhythmias resistant to

antiarrhythmic therapy

■Metabolic: hypocalcemia due to impaired release or action of PTH,

hypokalemia from renal potassium wasting; hypophosphatemia

tests

Laboratory

■basic studies: blood

■serum magnesium <1.5 mEq/L (may be falsely higher if patient is

initially dehydrated)

➣intracellular Mg may be depleted even if serum level is normal;

symptoms may occur with normal serum levels (no easy way of

measuring intracellular Mg clinically)

differential diagnosis

■Hypocalcemia, hypokalemia may cause some similar symptoms,

often coexist (hypocalcemia is resistant to calcium and Vitamin D

Rx; hypokalemia resistant to K supplements)

management

What to Do First

■assess severity of symptoms and renal function (Mg is cleared by the

kidney)

General Measures

■Treat underlying cause, adequate diet if possible (vegetables, meats,

legumes, nuts)