Magnesium is an important electrolyte that plays an essential role in hundreds of metabolic reactions in the body. Hypomagnesemia is an electrolyte disturbance caused by low serum magnesium — the amount of magnesium in the blood. The normal range for serum magnesium is 1.46 to 2.68 mg/dL. Hypomagnesemia is anything below 1.46 mg/dL. If left untreated, low magnesium can have devastating effects.
Hypomagnesemia is a dangerous electrolyte deficiency because magnesium is needed for so many reactions in the body, including nerve and muscle function, controlling blood glucose, and regulating blood pressure. Magnesium plays a role in energy production and the synthesis of DNA, RNA, and bone. It also helps transport other electrolytes, making it essential for muscle contraction, nerve conduction, and maintaining a normal heart rhythm.
The symptoms of hypomagnesemia vary because it affects so many functions in the body. Neuromuscular symptoms include numbness and tingling, seizures, muscle cramps and spasms, tremors, delirium, apathy, and even coma. Cardiovascular symptoms include irregular heartbeat, atrial fibrillation, atrial and ventricular arrhythmias, and cardiac cell death. Digestive symptoms like anorexia, nausea, and vomiting also occur. Hypomagnesium also affects the use of other electrolytes in the body, including calcium and potassium, and affects the production of parathyroid hormone.
Clinicians check for Trousseau sign and Chvostek sign when examining a patient for signs and symptoms indicating hypomagnesemia. The doctor keeps an inflated blood pressure cuff on the patient's arm for two or three minutes, reducing the blood supply to the wrist. When calcium is low, the wrist will spasm. Chvostek sign is involuntary twitching in the face when the doctor lightly taps the facial nerve. Both of these tests assess for low calcium, which is commonly secondary to low magnesium.
Hypomagnesemia leads to low calcium because these two electrolytes are closely related. Low magnesium leads to low levels of parathyroid hormone, which regulates calcium levels. Calcium plays many important roles in the body, including muscle contraction, forming bone and teeth, blood clotting, and maintaining normal heart rhythms.
There are many causes of hypomagnesemia. It often occurs due to decreased intake or malnutrition from alcoholism or starvation, or in critically sick people who receive intervenous nutrition. Some medications can also cause hypomagnesemia, including antibiotics, proton pump inhibitors, antifungals, loop and thiazide diuretics, arrhythmia medications, and chemotherapy drugs.
Hypomagnesemia can also result from gastrointestinal and kidney issues that interfere with the absorption of magnesium. These include acute or chronic diarrhea, gastric bypass surgery, acute pancreatitis, inherited kidney disorders, and rare genetic disorders. Hungry bone syndrome is an uncommon condition that causes increased magnesium uptake after the removal of the thyroid or parathyroid gland, leading to low serum magnesium.
Doctors suspect hypomagnesemia if a patient is experiencing unexplained neurological symptoms or chronic diarrhea, has an alcohol use disorder, or has used a medication known to cause low magnesium for a long time. A positive Trousseau sign and Chvostek sign often appear during the physical exam. A simple blood test confirms the diagnosis of hypomagnesemia. The doctor will also typically check for low calcium and potassium in the blood.
Treatment for hypomagnesemia depends on the symptoms and severity of the deficiency. Oral magnesium salts are often used, but some people with hypomagnesemia cannot tolerate anything by mouth and may require IV or IM supplementation. Magnesium is usually only given via IV in patients experiencing severe cases.
Hypomagnesemia affects only two percent of the general population, but it is more common in specific demographics. For example, it affects ten to 20 percent of hospitalized patients and as many as 60 percent of patients in intensive care. Up to 80 percent of people with alcohol use disorder and 25 percent of those with diabetes have hypomagnesemia.
Hypomagnesemia with secondary hypocalcemia is a rare genetic condition that causes low serum magnesium. It is an autosomal recessive disease, meaning that a copy of the defective gene is inherited from each parent. As parathyroid hormone and calcium levels are so closely related to magnesium, this disease affects them also. If not treated effectively, hypomagnesemia with secondary hypocalcemia causes movement disorders and heart failure and can be fatal.
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