Plasma ACTH levels in ACTH-dependent Cushing syndrome are typically:

• A. Low
• B. Normal
• C. High
• D. Absent

Answer: (C)

ACTH-dependent Cushing syndrome is driven by an ACTH-producing source, such as a pituitary adenoma or ectopic ACTH-secreting tumor. This means ACTH is elevated or inappropriately normal even though cortisol is high. The adrenal glands respond to the excess ACTH by making more cortisol, but unlike normal feedback, the ACTH source in these cases remains autonomous, so ACTH levels stay high. In contrast, ACTH-independent Cushing (from an adrenal tumor) typically shows suppressed ACTH due to negative feedback. So the plasma ACTH level is typically high.