A 72-year-old woman undergoes parathyroidectomy for primary hyperparathyroidism. Prior to surgery she complained of bone pain and had a compression fracture of the T11 vertebra.
Laboratory results from the day before surgery are as follows:

The patient had normal serum calcium on the first postoperative day. She was discharged with a prescription for calcium and vitamin D. Two days after surgery, she comes to the emergency department complaining of perioral numbness and spasms of both hands. On examination, she appears anxious. Her vital signs are normal except for a respiratory rate of 24/min. Chvostek's sign is positive.
Which of the following laboratory results would be expected from blood drawn at this time?

Question

A 72-year-old woman undergoes parathyroidectomy for primary hyperparathyroidism.  Prior to surgery she complained of bone pain and had a compression fracture of the T11 vertebra.
Laboratory results from the day before surgery are as follows:

The patient had normal serum calcium on the first postoperative day.  She was discharged with a prescription for calcium and vitamin D.  Two days after surgery, she comes to the emergency department complaining of perioral numbness and spasms of both hands.  On examination, she appears anxious.  Her vital signs are normal except for a respiratory rate of 24/min.  Chvostek's sign is positive.
Which of the following laboratory results would be expected from blood drawn at this time?

Quizplus · Accepted Answer

This patient presents with symptoms of hypocalcemia after parathyroidectomy. Transient mild hypocalcemia (lasting 1 week) can occur in patients with normal renal function after parathyroidectomy. This is due to decreased bone and intestinal calcium absorption from functional/relative hypoparathyroidism. Hungry bone syndrome occurs in patients with severe hyperparathyroidism (primary or secondary) and preoperative bone disease and results in severe and/or prolonged postoperative hypocalcemia. Patients with hyperparathyroidism have increased bone formation and resorption resulting in net efflux of calcium from bones. Acute withdrawal of parathyroid hormone (PTH) (eg, surgery) results in an imbalance between bone formation and resorption, resulting in net influx of calcium into the bone. PTH levels are usually normal but can also be elevated. Phosphate and magnesium are also reabsorbed along with calcium, resulting in hypophosphatemia and hypomagnesemia. Hypocalcemia is usually observed 2-4 days postoperatively; therefore, monitoring of serum calcium levels 2-4 times a day and oral repletion are recommended. IV calcium should be given in severe cases, with signs of respiratory distress, tetany, or serum calcium < 7.5 mg/dL. Magnesium should be administered as low levels diminish PTH secretion and can contribute to development of refractory hypocalcemia. However, phosphorus should not be administered unless serum levels are very low (< 1 mg/dL), as it can further exacerbate hypocalcemia. (Choice A) High calcium, low phosphorus, and high PTH are indicative of persistent primary hyperparathyroidism, which should not cause symptoms of hypocalcemia. It is unlikely that this patient has persistent hyperparathyroidism with normal calcium postoperatively. (Choice B) Low calcium, high phosphorus, and high PTH are usually seen in patients with chronic kidney disease due to impaired vitamin D metabolism. (Choice D) Hyperventilation leading to respiratory alkalosis lowers ionized calcium due to increased binding of calcium to albumin. Total calcium levels are normal in hyperventilation syndromes. Although hyperventilation could contribute to tetany in this patient, her recent parathyroidectomy makes hungry bone syndrome the most likely etiology. Educational objective: Risk factors for developing hungry bone syndrome after parathyroidectomy include moderate-to-severe hyperparathyroidism with evidence of high bone turnover, older age, and renal dysfunction. Laboratory findings include low calcium, low phosphorus, low magnesium, and normal (or high) PTH levels. __________ References: Hungry bone syndrome: clinical and biochemical predictors of its occurrence after parathyroid surgery. (http://www.ncbi.nlm.nih.gov/pubmed/3400660) Postoperative hungry bone syndrome in patients with secondary hyperparathyroidism of renal origin. (http://www.ncbi.nlm.nih.gov/pubmed/22399154) Hypophosphatemia and hungry bone syndrome in a dialysis patient with secondary hyperparathyroidism treated with cinacalcet--proposal for an improved monitoring. (http://www.ncbi.nlm.nih.gov/pubmed/17175888)

A 72-Year-Old Woman Undergoes Parathyroidectomy for Primary Hyperparathyroidism