A 45-year-old man is evaluated for a progressively enlarging neck mass and hoarseness. Physical examination shows an enlarged and nontender left thyroid lobe. Fine-needle aspiration biopsy is positive for papillary thyroid cancer, and a thyroidectomy is subsequently performed. On the second postoperative day, the patient develops tingling around the mouth and muscle cramps in his lower extremities. Blood pressure is 120/80 mm Hg, pulse is 82/min, and respirations are 14/min. Physical examination shows normal muscle strength and deep tendon reflexes. Light tapping anterior to the ear elicits twitching of the lower facial muscles. An increase in which of the following best explains this patient's current symptoms?

Question

A 45-year-old man is evaluated for a progressively enlarging neck mass and hoarseness.  Physical examination shows an enlarged and nontender left thyroid lobe.  Fine-needle aspiration biopsy is positive for papillary thyroid cancer, and a thyroidectomy is subsequently performed.  On the second postoperative day, the patient develops tingling around the mouth and muscle cramps in his lower extremities.  Blood pressure is 120/80 mm Hg, pulse is 82/min, and respirations are 14/min.  Physical examination shows normal muscle strength and deep tendon reflexes.  Light tapping anterior to the ear elicits twitching of the lower facial muscles.  An increase in which of the following best explains this patient's current symptoms?

Quizplus · Accepted Answer

11ec160b_3cf8_4ebe_9249_e7854d4a83e8_MD0001_00 This patient has perioral paresthesias and a positive Chvostek sign, which are typical manifestations of acute hypocalcemia. Hypocalcemia is a common complication of thyroid surgery due to iatrogenic injury (eg, devascularization, inadvertent removal) to the parathyroid glands and subsequent hypoparathyroidism. Calcium and phosphate homeostasis is regulated by 2 primary hormones: parathyroid hormone (PTH), which regulates minute-to-minute concentrations, and vitamin D, which regulates levels over the longer term. PTH is a polypeptide hormone that is produced by the chief cells of the parathyroid glands in response to hypocalcemia and has 3 primary effects: Acute hypoparathyroidism results in decreased calcium and phosphate release from bone (Choice B) and decreased calcium reabsorption by the kidneys. Inadequate PTH also reduces phosphate excretion by the kidneys and decreases the hydroxylation of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (the more active form) in the renal tubular cells (Choice C). This, in turn, decreases intestinal absorption of calcium and phosphate (Choice D). (Choice A) Elevated plasma pH enhances the binding of calcium to albumin, which leading to a precipitous drop in ionized calcium concentration that can induce symptoms of hypocalcemia. However, this patient has no indication of a respiratory (eg, tachypnea) or metabolic (eg, vomiting, hypovolemia) alkalosis. Educational objective: Postoperative hypocalcemia is common after thyroid surgery, due to inadvertent removal or damage to the parathyroid glands. The acute drop in parathyroid hormone level results in decreased calcium and phosphate resorption from bone and decreased calcium reabsorption by the kidneys. __________ References: Parathyroid disorders. (http://www.ncbi.nlm.nih.gov/pubmed/23944728) Defining the syndromes of parathyroid failure after total thyroidectomy. (http://www.ncbi.nlm.nih.gov/pubmed/25713783)

A 45-Year-Old Man Is Evaluated for a Progressively Enlarging Neck