Hypomagnesemia
is common among hospitalized patients and frequently occurs with other
electrolyte disorders, including hypokalemia and hypocalcemia. Magnesium
depletion usually results from inadequate intake plus impairment of renal
conservation or gastrointestinal absorption.
Drugs
can cause hypomagnesemia. Examples include chronic (> 1 year) use of a
proton pump inhibitor and concomitant use of diuretics. Amphotericin B can
cause hypomagnesemia, hypokalemia, and acute kidney injury. The risk of each of
these is increased with duration of therapy with amphotericin B and concomitant
use of another nephrotoxic agent. Liposomal amphotericin B is less likely to
cause either kidney injury or hypomagnesemia.
Trousseau
sign is the precipitation of carpal spasm by reduction of the blood supply to
the hand with a tourniquet or blood pressure cuff inflated to 20 mm Hg above
systolic blood pressure applied to the forearm for 3 minutes.
Chvostek
sign is an involuntary twitching of the facial muscles elicited by a light
tapping of the facial nerve just anterior to the exterior auditory meatus.
Serum
magnesium concentration < 1.8 mg/dL
Hypomagnesemia
is diagnosed by measurement of serum magnesium concentration.
Severe
hypomagnesemia usually results in concentrations of < 1.25 mg/dL.
Associated
hypocalcemia and hypocalciuria are common.
Hypokalemia
with increased urinary potassium excretion and metabolic alkalosis may be
present.
Treatment
with magnesium salts is indicated when magnesium deficiency is symptomatic or
the magnesium concentration is persistently < 1.25 mg/dL. Patients with
alcohol use disorder are treated empirically. In such patients, deficits
approaching 12 to 24 mg/kg are possible.
