Hypocalcemia after thyroidectomy — ABIM Board MCQ

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EasyEndocrinology/MetabolismHypocalcemia after thyroidectomyABIM Board

A 46-year-old woman develops perioral numbness and carpopedal spasm 2 days after total thyroidectomy. Her corrected serum calcium is 7.1 mg/dL, phosphate is 6.2 mg/dL, parathyroid hormone is low, and magnesium is normal. Which of the following is the most likely cause of these findings?

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Correct answer: E — Postoperative hypoparathyroidism

The correct answer is E. Total thyroidectomy can inadvertently remove, injure, or devascularize the parathyroid glands, causing transient or permanent postoperative hypoparathyroidism. Loss of parathyroid hormone decreases renal calcium reabsorption and reduces renal phosphate excretion, producing hypocalcemia with hyperphosphatemia. Perioral numbness and carpopedal spasm reflect hypocalcemic neuromuscular irritability. Normal magnesium excludes severe hypomagnesemia as a cause of impaired parathyroid hormone secretion. Vitamin D intoxication and primary hyperparathyroidism generally cause hypercalcemia. Tumor lysis syndrome can cause hypocalcemia and hyperphosphatemia but requires an appropriate malignancy and treatment context, often with hyperuricemia and acute kidney injury. Pseudohypoparathyroidism causes parathyroid hormone resistance and therefore an elevated, rather than low, parathyroid hormone level.

Reference: American Thyroid Association, American Thyroid Association Statement on Postoperative Hypoparathyroidism: Diagnosis, Prevention, and Management in Adults, 2018. https://pubmed.ncbi.nlm.nih.gov/29848235/