Muscular tetany

Specialty: Endocrine and metabolic.

• carpopedal spasm
• excitatory neuromuscular hyporeflexia
• metabolic tetanic contracture

Why it occurs

• Post-surgical hypoparathyroidism (injury or accidental removal of the parathyroid glands during a thyroidectomy or cervical dissection)
• Severe vitamin D deficiency (nutritional or malabsorption osteomalacia with impaired intestinal calcium absorption)
• Severe hypomagnesemia (magnesium levels below 1.0 mg/dL inhibit the release of PTH from vesicles and cause peripheral resistance to its action in the bone and kidney)
• Acute respiratory alkalosis (hyperventilation decreases the plasma concentration of free hydrogen ions, which increases the binding of calcium to albumin and drastically reduces the fraction of metabolically active ionized calcium)
• Acute necrotizing pancreatitis (calcium saponification in the peripancreatic adipose tissue that produces an acute decrease in serum calcium)

Initial workup

Immediate determination of total and ionized (free) serum calcium; serum phosphorus and magnesium; intact parathyroid hormone (iPTH) in serum; 25-hydroxyvitamin D levels; arterial blood gas to quantify pH and pCO2; and 12-lead electrocardiogram with continuous monitoring of the corrected QT interval (QTc).

Standard management

• 10% calcium gluconate — administration of 1-2 ampoules of 10 ml dissolved in 100 ml of 5% glucose solution to be administered intravenously in 10-20 minutes under electrocardiographic monitoring, taking care not to extravasate due to the risk of tissue necrosis
• Calcitriol — orally active vitamin D at doses of 0.25-1.0 mcg/day to facilitate rapid intestinal absorption of calcium independent of PTH
• Calcium carbonate — 1-3 grams of elemental calcium orally distributed with main meals as long-term maintenance therapy
• Magnesium sulfate — 1-2 grams intravenously in slow infusion in case of concomitant hypomagnesemia that perpetuates hypocalcemia