A patient with long-term asthma develops Cushing syndrome. What is the cause of this condition?

A. Lacking ACTH, related to the pituitary: Low ACTH (secondary adrenal insufficiency) causes features of adrenal failure rather than Cushing syndrome. B. Taking corticosteroids for many years: Prolonged exogenous corticosteroid therapy is a common cause of iatrogenic Cushing syndrome due to sustained high glucocorticoid exposure. C. Abruptly withdrawing cortisone therapy: Sudden withdrawal of steroids causes adrenal insufficiency symptoms, not Cushing syndrome. D. Poorly functioning adrenal glands: Adrenal hypofunction leads to insufficiency (e.g., Addison’s), whereas Cushing’s reflects cortisol excess.