This patient had hypercalcemia with a suppressed parathyroid hormone level. What is the diagnosis?
**Core Concept**
Hypercalcemia with a suppressed parathyroid hormone (PTH) level suggests an abnormality in calcium regulation, likely due to an external factor overriding the normal PTH-mediated feedback mechanism. This condition is characterized by high calcium levels despite decreased PTH production, indicating a non-parathyroid cause of hypercalcemia.
**Why the Correct Answer is Right**
The suppressed PTH level indicates that the body is trying to reduce calcium levels, but an external factor is causing an increase in serum calcium. This can be due to increased calcium absorption from the gut, increased bone resorption, or increased calcium release from other sources such as milk-alkali syndrome or vitamin D intoxication. In this patient, the suppressed PTH level suggests that the hypercalcemia is not due to primary hyperparathyroidism but rather to an external factor that is increasing calcium levels.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because primary hyperparathyroidism would typically present with an elevated PTH level, not suppressed.
**Option B:** This option is incorrect because familial hypocalciuric hypercalcemia (FHH) is a rare genetic disorder characterized by hypercalcemia and elevated or inappropriately normal PTH levels, not suppressed PTH.
**Option C:** This option is incorrect because malignancy-associated hypercalcemia typically presents with elevated PTH-related protein (PTHrP) levels, which can stimulate osteoclast activity and increase bone resorption, but this would not suppress PTH levels.
**Clinical Pearl / High-Yield Fact**
Milk-alkali syndrome, caused by excessive ingestion of calcium and absorbable alkali, can lead to hypercalcemia and metabolic alkalosis. This is a common cause of hypercalcemia in patients with normal or suppressed PTH levels.
**Correct Answer:** C.