In primary hyperparathyroidism, which bone disorder is characterized by high bone turnover and elevated alkaline phosphatase?

In primary hyperparathyroidism, which bone disorder is characterized by high bone turnover and elevated alkaline phosphatase?

• A. Osteoporosis
• B. Osteitis fibrosa cystica
• C. Osteomalacia
• D. Paget disease

Answer: (B)

In primary hyperparathyroidism, excess parathyroid hormone drives bone remodeling by boosting osteoclast activity (via osteoblast signals), which increases bone resorption. As the bone turnover ramps up, osteoblasts also work harder to lay down new bone, so alkaline phosphatase—an enzyme produced by osteoblasts—rises. This pattern of high turnover with elevated alkaline phosphatase is classic for osteitis fibrosa cystica, the severe bone manifestation of hyperparathyroidism, featuring subperiosteal bone resorption and fibrous/cystic changes. Osteoporosis involves low bone mass with relatively less compensatory turnover, so alkaline phosphatase is not characteristically elevated. Osteomalacia is due to defective mineralization (often from vitamin D deficiency) and also shows high alkaline phosphatase, but its primary driver is mineralization failure rather than excess PTH-driven resorption. Paget disease is a high-turnover disorder as well, with elevated alkaline phosphatase, but it is a distinct remodeling process not caused by primary hyperparathyroidism.

In primary hyperparathyroidism, excess parathyroid hormone drives bone remodeling by boosting osteoclast activity (via osteoblast signals), which increases bone resorption. As the bone turnover ramps up, osteoblasts also work harder to lay down new bone, so alkaline phosphatase—an enzyme produced by osteoblasts—rises. This pattern of high turnover with elevated alkaline phosphatase is classic for osteitis fibrosa cystica, the severe bone manifestation of hyperparathyroidism, featuring subperiosteal bone resorption and fibrous/cystic changes.

Osteoporosis involves low bone mass with relatively less compensatory turnover, so alkaline phosphatase is not characteristically elevated. Osteomalacia is due to defective mineralization (often from vitamin D deficiency) and also shows high alkaline phosphatase, but its primary driver is mineralization failure rather than excess PTH-driven resorption. Paget disease is a high-turnover disorder as well, with elevated alkaline phosphatase, but it is a distinct remodeling process not caused by primary hyperparathyroidism.