A 20 year old woman presents to your office complaining of "bugs crawling under her skin." She points all over her body and says she can feel mites crawling from one part of her body to the other. This has been going on for a while but the onset has been insidious, maybe over months to years. She has a history of dermatologic complaints like rashes, pruritis, and sensations of stinging or biting. She has gone to multiple physicians without relief. Today, she's brought in a specimen which she has picked from her skin; it just looks like flaky dry scales. When you confront her, she is offended, saying that she knows all about this bug's life cycle: when it's most active, when it reproduces, how it enters and leaves the body.
She has no medical or psychiatric problems other than polysubstance abuse and no history of head injuries. There is no objective evidence for any infection.
Challenge: What is the diagnosis and most likely etiology?