Review Question - QID 101951

The patient suffers from primary hyperparathyroidism, which has likely lead to the formation of a calcium oxalate kidney stone. PTH indirectly stimulates osteoclasts by binding to its receptor on osteoblasts, inducing RANK-L and M-CSF synthesis.

Primary hyperparathyroidism is the most common cause of hypercalcemia, aside from paraneoplastic syndrome. The typical patient is a postmenopausal woman with a benign adenoma. PTH raises serum calcium levels by indirectly stimulating osteoclasts. PTH binds PTH-R on osteoblasts which induces the production of RANK-L and M-CSF, that stimulate maturation of osteoclasts which break down bone increasing serum calcium. Phosphorous is lost via the urine, leading to a high ratio of chloride to phosphorous.

Taniegra reports that hyperparathyroidism is the most frequent cause of hypercalcemia in ambulatory (non-hospitalized) patients. The population most commonly involved is most postmenopausal women. Increased serum calcium levels classically present with calcium kidney stones, constipation, and systemic muscle aches or “stones, moans, and groans”. However, most people have no symptoms. Management of severe hypercalcemia can be achieved through IV hydration, followed by furosemide after volume repletion is assured. Adenomas are surgically removed.

Pasieka explains that hyperparathyroidism is a biochemical diagnosis (as calcium levels are often drawn on routine metabolic profiles) and typically diagnosed much earlier than because of clinical symptoms.

Illustration A diagrams the relationship between RANKL and osteoclasts.

Incorrect Answers:
Answer 1: PTH binds to receptors on osteoblasts.
Answer 2: Calcitonin lowers serum calcium levels.
Answer 4: PTH leads to increased M-CSF.
Answer 5: Osteoblasts synthesize osteoid, later mineralized with Ca to form new bone.