Hypoparathyroidism

Pt with h/o autoimmune disorders s/p neck surgery presents with tetany, seizures. Not actively seizing; reports recent paresthesias, emotional lability, anxiety/depression, and difficulty focusing. Hypotension, cataract, irregular heartbeat, positive Chvostek/Trousseau sign, lower extremity edema, and dry skin on exam.

  • Labs

    • CMP shows hypocalcemia with normal albumin

    • PTH level inappropriately low in the setting of hypocalcemia

    • Obtain repeat CMP; if repeat level is low

      • Obtain serum ionized calcium

      • Obtain serum 25-hydroxyvitamin D and magnesium levels to rule out alternate causes of hypocalcemia

  • EKG shows QTc > 500 milliseconds

  • Administer 2g calcium gluconate over 30 minutes; replete to corrected calcium level of 8.0 (see notes for further repletion options)

Notes

  • Etiologies

    • Most common: Parathyroid damage during neck surgery

    • Autoimmune destruction of parathyroid glands

  • Potential signs/symptoms of hypocalcemia include cataract, arrhythmia, refractory heart failure (edema), tetany, seizures, altered mental status

  • PTH and serum calcium

    • Corrected Ca = [0.8 x (normal albumin - patient's albumin)] + serum Ca

    • Normal PTH level = 10-65 mg/dL

    • Normal PTH in setting of low calcium also indicates hypoparathyroidism

  • Calcium repletion

    • 1g calcium is equivalent to

      • CaCO3 250 mg PO

      • Calcium gluconate 1g IV over 30 minutes

    • Corrected calcium < 7.5 mg/dL with arrhythmia and/or seizure:

      • Start 2g IV calcium over 30 minutes

      • Notify ICU as transfer may be necessary if symptoms do not resolve. (Administering greater than 2g of calcium over 30 minutes requires a central line.)

      • Repeat CMP in 4 hours

    • Corrected calcium < 7.5 mg/dL with mild symptoms (e.g. paresthesias) and/or QTc > 500 milliseconds but no arrhythmia:

      • Obtain serum ionized calcium to confirm hypocalcemia

      • Administer 1g calcium (preferably PO) and repeat CMP in 12 hours

    • 7.5 or greater and no symptoms: Consider starting 1g calcium carbonate PO and monitor with daily CMP