Which condition is associated with increased levels of adrenocorticotropic hormone (ACTH)?

Increased levels of adrenocorticotropic hormone (ACTH) are primarily associated with Cushing's syndrome. This condition arises due to an excess of cortisol, which can be a result of various factors, including tumors of the pituitary gland that secrete ACTH or tumors that produce cortisol directly. When cortisol levels are elevated, the body signals the pituitary gland to reduce ACTH production through a negative feedback mechanism. However, in cases of Cushing's syndrome caused by an adrenal tumor or ectopic ACTH production from tumors outside of the pituitary, ACTH levels can remain elevated despite high cortisol levels.

This is contrasted with other conditions listed. For example, thyroid storm is characterized by an extreme hyperthyroid state and does not involve ACTH. Diabetes mellitus primarily relates to insulin resistance or deficiency, and while hormonal imbalances may exist, they do not typically feature increased ACTH levels. Youth obesity, while it can have various hormonal implications, does not directly correlate with increased ACTH. Therefore, the link between Cushing's syndrome and elevated ACTH levels is clear, making it the correct answer in this context.