Darkened Epidermis

A 31-year-old woman presents with ongoing weakness and malaise and says her skin seems to be getting darker without exposure to the sun. Your Dx?

A 31-year-old woman complains of episodes of weakness, upper abdominal discomfort, and nausea for the past 6 months. She also states that her skin appears to be getting darker even though she spends no more time in the sun than usual. Her hand is seen on the right in the Figure next to that of her treating physician.

 

What's your diagnosis?