**Core Concept**
The patient's symptoms and physical examination findings are suggestive of hyperthyroidism, specifically Graves' disease, an autoimmune disorder characterized by excessive thyroid hormone production. In Graves' disease, the immune system produces antibodies that stimulate the thyroid-stimulating hormone receptor, leading to increased thyroid hormone secretion.

**Why the Correct Answer is Right**
In Graves' disease, the thyroid gland is stimulated to produce more thyroid hormones, including thyroglobulin, a protein produced by the thyroid gland that serves as a precursor to thyroid hormones. An increased plasma concentration of thyroglobulin is therefore expected in this condition, reflecting the increased thyroid hormone production. This is in contrast to other forms of hyperthyroidism, such as toxic multinodular goiter or thyroiditis, where thyroglobulin levels may be decreased.

**Why Each Wrong Option is Incorrect**
**Option A:** Decreased serum T4 is not expected in Graves' disease, where T4 levels are typically elevated due to excessive thyroid hormone production.
**Option B:** Decreased radioactive iodine uptake is characteristic of thyroiditis, where the thyroid gland is inflamed and unable to take up iodine, whereas in Graves' disease, radioactive iodine uptake is typically increased.
**Option C:** Decreased resin T3 uptake is not a specific finding in Graves' disease, and this option is more relevant to conditions where T3 levels are decreased, such as hypothyroidism.

**Clinical Pearl / High-Yield Fact**
In Graves' disease, the presence of exophthalmos (bulging eyes) is a classic clinical finding, often associated with a more aggressive disease course. This is due to the autoimmune nature of the disease, which can lead to inflammation and swelling of the tissues around the eye.

**✓ Correct Answer: D. Increased plasma concentration of thyroglobulin**