Hypoparathyroidism

The post-thyroidectomy window - This is where you will meet it. PTH clears in minutes, so ionized calcium can fall within hours of the operation. Send an ionized calcium, or total calcium with albumin, rather than waiting on symptoms.

Stridor after neck surgery - Severe hypocalcemia causes laryngospasm and tetany, and it sits on the differential alongside an expanding neck hematoma, which compresses the trachea and congests the airway. Hematoma means immediate wound opening and re-exploration, and intubation should not be delayed; hypocalcemia means IV calcium.

Bedside signs - Chvostek's sign, a facial twitch on tapping the facial nerve, and Trousseau's sign, carpopedal spasm on cuff inflation, are both positive with hypocalcemia, along with perioral numbness and muscle cramps.

Acute IV calcium - Calcium gluconate over calcium chloride: chloride causes tissue necrosis on extravasation and should go through a central line. A 10 mL ampule of 10% calcium gluconate is 1 g of salt but only 93 mg of elemental calcium. Give 1 to 2 ampules diluted in D5W over 10 to 20 minutes and recheck calcium in a few hours, or run 3 to 5 g of 10% calcium gluconate in a liter of D5W at 50 mg of elemental calcium per hour.

Send a magnesium with the calcium - If hypomagnesemia is the cause, calcium alone corrects it only temporarily. Replete magnesium or the calcium will not hold.

ECG before you stack drugs - Low ionized calcium weakens myocardial contraction and prolongs the QT interval, and long-standing untreated disease causes dilated cardiomyopathy. Get a baseline 12-lead and think twice about additional QT-prolonging agents.

Continue the home regimen - These patients live on calcium plus calcitriol. Confirm the doses were taken and get a preop calcium, phosphorus, and creatinine: chronic therapy carries a real risk of nephrolithiasis, nephrocalcinosis, and renal insufficiency, which changes your renally cleared drug choices.

Seizures and weakness - Severe hypocalcemia seizes, and chronic disease produces a skeletal muscle myopathy. If a hypoparathyroid patient convulses in PACU, send a calcium before you reach for anything else.

Hypoparathyroidism is deficient parathyroid hormone (PTH), producing hypocalcemia, hyperphosphatemia, and increased neuromuscular irritability. PTH normally raises serum calcium three ways: resorption from bone, increased distal tubular calcium reabsorption with decreased proximal phosphate reabsorption, and activation of renal 1-alpha-hydroxylase to make 1,25-dihydroxyvitamin D for gut absorption. Its serum half-life is only a few minutes, so calcium falls fast once the glands are damaged.

Most cases are surgical - thyroidectomy and other head and neck operations. The rest are autoimmune (polyglandular autoimmune syndrome type 1), congenital (DiGeorge), or driven by hypomagnesemia. Clinically it runs from perioral numbness, paresthesias, and carpopedal spasm to laryngospasm, tetany, and seizures. Untreated chronic disease adds QT prolongation, dilated cardiomyopathy, and skeletal muscle myopathy.