**Core Concept**
Subperiosteal resorption and increased skull thickness are characteristic features of a specific endocrine disorder. This condition is related to an excess of a particular hormone that affects bone metabolism.

**Why the Correct Answer is Right**
The correct answer is associated with an excess of parathyroid hormone (PTH), which stimulates osteoclasts to break down bone, leading to subperiosteal resorption. The increased PTH levels also stimulate osteoblasts to deposit new bone, resulting in increased skull thickness. This condition is a classic sign of primary hyperparathyroidism, a disorder that arises from an overactive parathyroid gland.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not directly related to subperiosteal resorption or increased skull thickness. While certain disorders can cause changes in bone density, they do not typically result in the characteristic features seen in the correct answer.
* **Option B:** This option is incorrect because it refers to a different endocrine disorder that affects thyroid hormone levels. While thyroid disorders can cause changes in bone metabolism, they do not typically result in subperiosteal resorption or increased skull thickness.
* **Option C:** This option is incorrect because it refers to a different condition that affects the skeletal system. While it can cause changes in bone density, it does not typically result in the characteristic features seen in the correct answer.

**Clinical Pearl / High-Yield Fact**
The presence of subperiosteal resorption, particularly in the context of increased skull thickness, should raise suspicion for primary hyperparathyroidism. This condition requires prompt evaluation and treatment to prevent complications such as osteoporosis, kidney stones, and cardiac calcification.

**Correct Answer:** D. Hyperparathyroidism.