A 45-year-old female presents to her primary care physician with complaints of weight gain, easy bruising, and a round, "moon-shaped" face. She also reports irregular menstrual cycles and excessive hair growth on her face and body. On physical examination, she has central obesity, purple striae on her abdomen, and thin skin. Laboratory studies reveal elevated serum cortisol levels and lack of suppression of cortisol with low-dose dexamethasone suppression test. Additionally, her plasma ACTH levels are found to be elevated. Which of the following features would suggest an ectopic source of ACTH as the underlying cause of her condition?