Diagnosis

Hypomagnesemia

Etiology

Causes [fs8]

• Starvation

• Critically ill patient

• Diabetes Mellitus

• Alcoholism: inadequate intake and excessive renal excretion

• GI losses: diarrhea, malabsorption (ulcerative colitis, Crohn disease, Gastric bypass surgery)

• Pregnancy: Preeclampsia/eclampsia, lactation

• Renal loss: Gitelmans syndrome, Bartter Syndrome, Hypercalcemia, Diabetic ketoacidosis, Hyperaldosteronism, hyperthyroidism, SIADH, Nephrotoxins, Familial hypomagnesemia with hypercalciuria and nephrocalcinosis, acute tubular dysfunction (post-kidney transplant, Postobstructive diuresis)

• Drugs: Diuretics (Loop, Thiazide, Mannitol), PPI, aminoglycosides, amphotericin B, foscarnet, pentamidine, calcineurin inhibitors, mTOR, potassium binders (resonium, patiromer), Digitalis, Cisplatin, Laxative, Insulin, Metformin, Terbutaline, Theophylline

• Extracellular to intracellular shift: Insulin, refeeding syndrome, correction of metabolic acidosis, pancreatitis

• Hungry bone syndrome (following parathyroidectomy or thyroidectomy)

Pathophysiology [fs8]

1. Magnesium is the second most abundant cation within the body’s cells, essential for:

   • Cellular function

   • Neurotransmission

   • Cardiac conduction

   • Cofactor in >300 enzyme reactions

   • Platelet function (clotting and thrombus formation)

   • Maintenance of vascular tone

   • Muscle contraction and relaxation

   • Insulin regulation

   • Bone formation

2. Despite magnesium's widespread presence in food sources, magnesium deficiency remains prevalent globally, even in developed nations [ueh]

3. Magnesium deficiency causes: [wo3][vqk][fs8]

   • Neuromuscular Manifestations

     • Neuromuscular hyperexcitability, tremor, tetany, muscle spasms, muscle cramps, choreoathetosis, seizure, nystagmus, apathy, delirium, depression, agitation, psychosis, delirium, coma

   • Cardiovascular Manifestations

     • ECG: wide QRS, peaked T waves, prolonged PR, diminution of the T wave

     • Atrial and ventricular premature systoles

     • Atrial fibrillation

     • Ventricular arrhythmias

     • Cardiac ischemia

     • Increased risk of digoxin toxicity

     • Vasoconstriction/vasospasm

     • Endothelial injury

     • Increased rate of thrombosis (risk factors for stroke)

     • Atherosclerosis

   • Electrolyte and Hormone Abnormalities

     • Hypocalcemia

     • Hypoparathyroidism

     • Hypokalemia

Complications [fs8]

• Fatal ventricular arrhythmia (torsades de pointes)

• Chondrocalcinosis

Epidemiology

Prevalence per 100.000 [fs8][97r][ueh][wo3][vqk]

Approach

• Blood test: Mg, Ca, phosphate, glucose, creatinine

• Urine: 24-hour Mg

• Fractional excretion of magnesium: (uMg x pCr) / (0.7 x pMg x uCr) [fs8]

• ECG

Treatment

Assessment of the severity of symptoms and determination of the etiology: [gsw]

1. Life-threatening symptoms (seizures and ventricular arrhythmias) [fs8]

   • Rapid stabilization: Magnesium sulfate 1-2g over 15 minutes IV

2. Eclampsia: 4-6g administered over 20-30 minutes

3. Nonemergency situations:

   • Discontinue drugs casing hypomagnesemia

   • Severe hypomagnesemia in a stable patient: Magnesium sulfate 1gram/hour IV

   • Oral magnesium 300mg per day: lack of empiric evidence regarding the oral bioavailability. Because of its poor absorption, magnesium is an effective osmotic laxative, and the severity of diarrhea increases linearly with the magnesium content of stool.

   • Subcutaneous delivery of magnesium sulfate has been used in intractable hypomagnesemia.

Differential diagnoses

Clostridium tetani, Diabetes mellitus, Hyperkalemia, Hyperphosphatemia, Hyperventilation, Hypocalcemia, Hypocapnia, Hypokalemia, Hypoparathyroidism, Milk-alkali syndrome