What is the usual cause of hypoparathyroidism?

• A. Removal of thyroid glands with accidental removal of parathyroid gland(s)
• B. Autoimmune destruction of the parathyroid glands
• C. Vitamin D deficiency
• D. Chronic kidney disease

Answer: (A)

The main thing this question tests is understanding what drives a drop in parathyroid hormone (PTH) and why certain conditions cause low PTH rather than low calcium for other reasons. The usual cause of hypoparathyroidism is damage or inadvertent removal of the parathyroid glands during thyroid surgery. The parathyroids are small glands located near or on the back of the thyroid; when the thyroid is removed or the blood supply to these glands is compromised, PTH secretion falls. Without enough PTH, calcium in the blood decreases, leading to hypoparathyroidism symptoms and the need for calcium/vitamin D management.

Autoimmune destruction of the parathyroids can cause hypoparathyroidism, but it’s much less common than post-surgical loss. Vitamin D deficiency lowers calcium by reducing absorption, but PTH is not suppressed; it’s usually elevated (secondary hyperparathyroidism) as the body tries to compensate. Chronic kidney disease also drives secondary hyperparathyroidism due to imbalances in phosphate and active vitamin D, not a primary drop in PTH.