**Core Concept**
Pretibial myxedema is a skin condition characterized by thickening of the skin due to an accumulation of mucin, a type of glycoprotein. This condition is associated with thyroid disease, particularly Graves' disease, where autoantibodies stimulate the thyroid gland to produce excess thyroid hormones.

**Why the Correct Answer is Right**
Pretibial myxedema is a complication of Graves' disease, an autoimmune disorder that leads to hyperthyroidism. The autoantibodies in Graves' disease stimulate the thyroid-stimulating hormone receptor (TSHR), causing an overproduction of thyroid hormones. This excess thyroid hormone production leads to the deposition of mucin in the skin, resulting in pretibial myxedema. The condition is often seen in patients with Graves' ophthalmopathy, another complication of Graves' disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to pretibial myxedema. Hashimoto's thyroiditis is an autoimmune disorder that leads to hypothyroidism, not hyperthyroidism.
* **Option B:** This option is not correct. Dermatomyositis is an autoimmune disorder that affects the skin and muscles, but it is not associated with thyroid disease or pretibial myxedema.
* **Option C:** This option is not relevant to pretibial myxedema. Scleroderma is an autoimmune disorder that affects the skin and connective tissue, but it is not associated with thyroid disease.

**Clinical Pearl / High-Yield Fact**
Pretibial myxedema is a classic sign of Graves' disease, and its presence should prompt a thorough evaluation for other complications of the disease, such as Graves' ophthalmopathy and thyroid storm.

**Correct Answer: D. Graves' disease.**