**Core Concept**
Primary hyperparathyroidism is a condition characterized by the excessive production of parathyroid hormone (PTH) due to a parathyroid gland disorder, leading to hypercalcemia. This excessive hormone secretion disrupts calcium homeostasis in the body.

**Why the Correct Answer is Right**
The correct answer, **Option C: Decreased calcium**, is incorrect because primary hyperparathyroidism is typically associated with hypercalcemia, not decreased calcium levels. Elevated PTH levels stimulate the release of calcium from bones and increase its absorption from the gut, leading to increased serum calcium concentrations. This is a key pathophysiological mechanism underlying the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Nephrolithiasis is a true statement about primary hyperparathyroidism. The excessive calcium levels can lead to the formation of kidney stones (nephrolithiasis).

**Option B:** Increased alkaline phosphatase is a true statement about primary hyperparathyroidism. Elevated PTH levels can stimulate bone turnover, leading to increased activity of osteoblasts and, consequently, elevated levels of alkaline phosphatase, a marker of bone formation.

**Option D:** Loss of lamina dura is a true statement about primary hyperparathyroidism. The excessive bone resorption associated with primary hyperparathyroidism can lead to the loss of the lamina dura, a dense layer of bone that surrounds the tooth sockets.

**Clinical Pearl / High-Yield Fact**
A classic clinical correlation for primary hyperparathyroidism is the presence of "brown tumors," which are actually areas of bone resorption and fibrosis that can occur as a result of the excessive PTH levels. These lesions can be a clue to the diagnosis in patients with hypercalcemia.

**✓ Correct Answer:** C. Decreased calcium