Enlarged thyroid, nervousness, and weight loss are symptoms of?

The symptoms of an enlarged thyroid, nervousness, and weight loss are indicative of Grave's disease, which is an autoimmune disorder that leads to hyperthyroidism. In this condition, the thyroid gland is overstimulated and produces excessive amounts of thyroid hormones, resulting in an increase in metabolic activities. This hypermetabolic state can cause symptoms such as significant weight loss, nervousness, anxiety, tremors, and an enlarged thyroid, also known as a goiter.

In contrast, the other conditions listed have distinct features that differ from those of Grave's disease. For instance, Cushing's syndrome is characterized by an excess of cortisol production and often presents with weight gain, not loss, along with symptoms like easy bruising and facial rounding. Addison's disease, which is characterized by insufficient production of adrenal hormones, often leads to fatigue, weight loss, and skin pigmentation changes. Myxedema, or severe hypothyroidism, results in symptoms such as weight gain, lethargy, and cold intolerance, rather than the elevated energy levels and severe weight loss seen in hyperthyroidism. Therefore, the accurate association of symptoms with Grave's disease clarifies why it is the correct answer.