A 35-year-old woman presents with palpitations, weight loss, anxiety, and heat intolerance. Labs show elevated free T4 and suppressed TSH. A radioactive iodine uptake scan reveals diffusely increased uptake. What is the most likely diagnosis?

✓ Correct Answer: Option C

The clinical presentation of hyperthyroidism with diffusely increased radioactive iodine uptake is classic for Graves' disease, an autoimmune condition causing thyroid overactivity. Subacute thyroiditis and factitious hyperthyroidism typically show decreased uptake.