Q. A 35-year-old female presents with a history of weight gain, easy bruising, and purple stretch marks on her skin. She reports having a round face and a fat deposit on the back of her neck. She also complains of fatigue and decreased libido. The patient denies any history of smoking or alcohol use. The patient has a history of polycystic ovary syndrome (PCOS) and has been on hormonal therapy for the past 5 years. She reports no other significant medical problems. The patient's family history is unremarkable. Vital signs are normal. The patient has central obesity, with a BMI of 40. There is excessive hair growth on her face, chest, and abdomen. Her skin is thin and easy to bruise. The patient has pigmentation on her neck, armpits, and groin area. Serum cortisol levels are elevated, and the results of a dexamethasone suppression test confirm the diagnosis of Cushing syndrome. Further testing reveals that the patient has a pituitary adenoma. What is the cause of hyperpigmentation seen in this patient?