Q. A 45-year-old woman presents to the clinic with a 3-month history of fatigue, hair loss, and a painful burning sensation in her feet. She also reports a recent onset of loose stools. Her past medical history is unremarkable except for an eating disorder that she has been struggling with for many years. On physical examination, she appears malnourished. Her hair is thin and sparse, and there are signs of dermatitis on her arms. There are no palpable goiters or masses in her neck. Lab tests reveal low cortisol levels. What is the most likely diagnosis in this patient?