Management of Hypoparathyroidism following Thyroidectomy – short note

Hypoparathyroidism following Thyroidectomy 

  • Introduction
    • Parathyroid glands produce parathyroid hormone
    • PTH increases serum calcium levels by
      • Stimulating synthesis vitamin D (1,25-dihydroxy vitamin D3)
        • Increases intestinal absorption of calcium
        • Causing bone resorption
        • Increasing renal absorption of calcium
      • Increases renal excretion of phosphorous
  • Inadequate production of PTH leads to hypocalcaemia
  • Incidence following thyroidectomy
    • Temporary hypocalcaemia =>2%
    • Permanent hypocalcaemia => 0.5 %
  • Mechanisms
    • Direct trauma to the parathyroid glands
    • Devascularisation of parathyroid glands
    • Removal of the glands during surgery
  • Risk factors for hypocalcaemia after thyroidectomy
    • Graves’ disease
    • Malignancy
    • Type of procedure =>  ↑ with total thyroidectomy, completion thyroidectomy
  • Presentation
    • Initially asymptomatic
    • Symptoms at 2 – 5 days
    • Circumoral paraesthesia
    • Mental status changes
    • Tetany / Carpopedal spasm
    • Laryngospasm
    • Seizures
    • QT prolongation on ECG
    • Cardiac arrest
  • Evaluation
    • Chvostek sign => tapping region of facial nerve in the pre auricular area resulting in facial contractions
    • Trousseau sign => carpopedal spasm elicited by inflation of a blood pressure cuff
    • Ionized calcium in the perioperative period
    • PTH level
      • Wong, et al => PTH levels < 1.5 pmol/l and morning serum calcium < 2.0 mmol/l => patients at risk of hypocalcaemia following total thyroidectomy
    • Rule out other causes
    • Renal failure (serum phosphorus will be raised)
    • Hypomagnesaemia
    • Medications
  • Prevention
    • Identify parathyroid glands during surgery
    • Maintain their blood supply
    • The surgical wound and the excised thyroid gland should be carefully examined for parathyroid tissue
    • Put tissue in normal saline => fat will float, parathyroid gland will sink
    • If removed or devascularized => cut into 1- to 2-mm pieces, and reimplant into a pocket created in the sternocleidomastoid muscle or strap muscle àlocation may be marked with a permanent suture or a metallic hemoclip for easier identification in any future surgeries 
  • Treatment
    • Asymptomatic hypocalcaemia  => no treatment
    • Symptomatic hypocalcaemia in the early postoperative period or whose calcium levels continue to fall rapidly require treatment
      • Intravenous calcium gluconate => 10 ml of 10% solution (1 g) iv over 10 minutes dissolved in 500 ml of 5% dextrose
      • Calcium infusion may be started at a rate of 1-2 mg/kg/h if symptoms do not resolve
      • Titrate the infusion to the patient’s symptoms and calcium levels
      • Once symptoms start subsiding => oral calcium => 1-2 gms/day
      • Vitamin D with calcitriol (Rocaltrol) 0.25-1 mcg/d
    • In 1-2 months, an attempt to wean the patient off oral calcium may be made to reveal if the hypoparathyroidism is temporary
    • Dependence on calcium supplementation for longer than 6 months usually indicates permanent hypoparathyroidism.