Ace the 2026 Calcium & Phosphate Metabolism Challenge – Master Your Metabolic Mojo!

Excess parathyroid hormone drives bone remodeling toward resorption, with a preferential impact on cortical bone. This results in a decrease in cortical bone mineral density, making bones thinner and more prone to fracture. In primary hyperparathyroidism, the high PTH level stimulates osteoclast activity indirectly through osteoblasts (increasing RANKL and reducing OPG), leading to high bone turnover and net loss of cortical bone, which is why decreased cortical BMD is the best-described bone finding. The other options don’t fit because PHPT does affect bones and typically does not cause osteosclerosis or normal bone density; instead, bone density tends to be reduced, particularly in the cortical compartment.