Dexamethasone is a drug used to suppress the secretion of ACTH from the anterior pituitary gland. Two patients with hypersecretion of cortisol are given dexamethasone. Anika's cortisol secretion level falls to normal after the medication, but Bonnie's cortisol secretion remains elevated. Which patient has primary hypercortisolism, also known as Cushing's syndrome? Explain your reasoning.