Most common cause of hypercalcemic crisis is –
**Core Concept**
Hypercalcemic crisis is a life-threatening condition characterized by extremely high levels of calcium in the blood. The underlying cause is often related to **hyperparathyroidism** or **malignancy**.
**Why the Correct Answer is Right**
The most common cause of hypercalcemic crisis is **hypercalcemia of malignancy**, which occurs when a tumor produces **parathyroid hormone-related protein (PTHrP)**, leading to increased osteoclastic activity and bone resorption.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while primary **hyperparathyroidism** can cause hypercalcemia, it is less common than malignancy-associated hypercalcemia.
**Option B:** Incorrect as **vitamin D toxicity** can cause hypercalcemia but is not the most common cause of hypercalcemic crisis.
**Option D:** Incorrect because **familial hypocalciuric hypercalcemia** is a rare genetic disorder that causes mild hypercalcemia, not a hypercalcemic crisis.
**Clinical Pearl / High-Yield Fact**
Hypercalcemic crisis is a medical emergency requiring prompt treatment, including **aggressive hydration** and **bisphosphonates** to reduce calcium levels.
**Correct Answer:** D. Hypercalcemia of malignancy