Inappropriate ACTH production refers to which condition?

• A. Ectopic Cushing syndrome
• B. Cushing's disease
• C. Primary hypercorticolism
• D. Addison's disease

Answer: (A)

Inappropriate ACTH production means ACTH remains elevated despite high cortisol, pointing to an ACTH-dependent form of Cushing's syndrome where the source is outside normal pituitary control. This best fits ectopic ACTH production, where a nonpituitary tumor (often a lung neuroendocrine tumor) secretes ACTH autonomously, driving excess cortisol. Addison's disease involves adrenal insufficiency with high ACTH and low cortisol, which is not what’s described here, and primary hypercortisolism is driven by the adrenal gland itself with suppressed ACTH. Cushing's disease does involve increased ACTH, but the source is a pituitary adenoma, whereas the term in question specifically describes ACTH coming from a nonpituitary source.