Which condition is most likely to present with hypocalcemia due to PTH unresponsiveness?

Which condition is most likely to present with hypocalcemia due to PTH unresponsiveness?

• A. Pseudohypoparathyroidism
• B. Primary hypoparathyroidism
• C. Primary hyperparathyroidism
• D. Osteoporosis

Answer: (A)

Hypocalcemia caused by PTH unresponsiveness comes from end-organ resistance to PTH rather than a deficiency of the hormone. In this situation, the glands may pump out PTH, but the kidney and bone don’t respond properly to it. That’s the hallmark of pseudohypoparathyroidism. Because the kidneys can’t respond to PTH, phosphate is not excreted effectively and calcium reabsorption is impaired, so serum calcium stays low and phosphate tends to be elevated. The PTH level is inappropriately high or normal given the low calcium, reflecting a hormone that’s present but not effective. This contrasts with primary hypoparathyroidism, where the problem is too little PTH produced, leading to low calcium but low or inappropriately normal PTH. Primary hyperparathyroidism elevates PTH and typically causes high calcium, not hypocalcemia. Osteoporosis affects bone density without causing the specific endocrine resistance pattern that drives hypocalcemia in pseudohypoparathyroidism.

Hypocalcemia caused by PTH unresponsiveness comes from end-organ resistance to PTH rather than a deficiency of the hormone. In this situation, the glands may pump out PTH, but the kidney and bone don’t respond properly to it. That’s the hallmark of pseudohypoparathyroidism. Because the kidneys can’t respond to PTH, phosphate is not excreted effectively and calcium reabsorption is impaired, so serum calcium stays low and phosphate tends to be elevated. The PTH level is inappropriately high or normal given the low calcium, reflecting a hormone that’s present but not effective.

This contrasts with primary hypoparathyroidism, where the problem is too little PTH produced, leading to low calcium but low or inappropriately normal PTH. Primary hyperparathyroidism elevates PTH and typically causes high calcium, not hypocalcemia. Osteoporosis affects bone density without causing the specific endocrine resistance pattern that drives hypocalcemia in pseudohypoparathyroidism.