Magnesium deficiency, or hypomagnesemia, is a condition in which serum levels of magnesium drop below 1.7 milligrams per decaliter of fluid, or mg/dL, according to the National Institutes of Health. According to the Nelson Textbook of Pediatrics, magnesium levels rarely fall below 1.5 mg/dL. Causes of magnesium deficiency include malabsorption syndromes like cystic fibrosis and Crohn's disease, alcoholism, laxative abuse, pancreatitis, aminoglycoside treatment and renal wasting syndromes.
Neuromuscular Signs
According to the article "Signs and Symptoms of Magnesium Depletion" by Dr. Zalman Agus, M.D., low magnesium levels manifest with characteristic neuromuscular signs such as tetany, generalized convulsions, generalized muscle weakness, apathy and deliurium. Diagnostic signs include positive Chvostek and Trousseau signs, which are indicative of neuromuscular irritability. A positive Chvostek sign occurs when tapping the cheek anterior to the earlobe causes the facial muscles on that side of the face to twitch. A spasm of the the wrist in response to placing a blood pressure cuff on the arm for three minutes is considered a positive Trousseau sign.
Low Magnesium and the Heart
Signs of hypomagnesemia show up on an electrocardiogram or EKG, according to "Harrison's Principles of Internal Medicine." The EKG changes most commonly seen in magnesium deficiency are the widening of the QRS complex and nonspecificT wave changes. The QRS complex represents the contraction of the ventricles, or two lower chambers of the heart. A wide QRS complex demonstrates profound cardiac muscle irritability. T wave changes indicate problems in relaxation of the ventricles. In more severe magnesium deficiencies, ventricular arrhythmias such as torsades do pointes and ventricular fibrillation occur.
Associated Electrolyte Imbalances
According to "Cecil Medicine," magnesium deficiencies are rarely isolated. Usual signs of hypomagnesemia are associated low blood levels of calcium and potassium. Magnesium deficiency impairs parathyroid hormone secretion, which in turn leads to decreased blood calcium. In terms of potassium, hypomagnesemia promotes renal potassium wasting, thus causing serum potassium levels to plummet.
References
- "Nelson Textbook of Pediatrics" 18th ed.; Robert Kliegman, M.D., et al.; 2007
- "Cecil Medicine" 23rd ed.; Lee Goldman, M.D. and Dennis Ausiello, M.D.; 2008
- "Brenner and Rector's The Kidney" 8th ed.; Barry Brenner, M.D.; 2008
- "UpToDate"; Signs and Symptoms of Magnesium Depletion; Zalman Agus, M.D.; May 2010
- "Harrison's Principles of Internal Medicine" 17th ed.; Anthony Fauci, M.D., et al..; 2008
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