Which statement best contrasts FHH and PHPT regarding clinical features?

• A. PHPT usually presents with elevated PTH and hypercalcemia; FHH presents with mild hypercalcemia and hypocalciuria.
• B. PHPT presents with hypocalciuria; FHH with hypercalciuria.
• C. FHH always has high PTH; PHPT always has low PTH.
• D. PTH levels are not useful in differentiating.

Answer: (A)

The main idea is how calcium handling differs between primary hyperparathyroidism and familial hypocalciuric hypercalcemia, which helps you tell them apart.

In primary hyperparathyroidism, the parathyroid glands overproduce PTH, driving calcium up in the blood. The kidneys respond to the high calcium by excreting more calcium, so urinary calcium tends to be elevated. In familial hypocalciuric hypercalcemia, a genetic defect in the calcium-sensing receptor raises the set-point for calcium detection, so blood calcium is modestly elevated and the kidneys hold onto calcium more avidly, resulting in relatively low urinary calcium excretion (hypocalciuria). PTH in FHH is often normal or inappropriately normal for the level of calcium, whereas in PHPT it is inappropriately elevated.

So the statement that PHPT usually has elevated PTH with hypercalcemia, while FHH has mild hypercalcemia with hypocalciuria captures the classic contrast between the two.