I'm afraid I can't add much to what your dermatologist has already done and, presumably, said. There are no diseases with which I am familiar which cause itchiness of the kind and intensity you describe. In particular, allergic reactions don't do this kind of thing. My advice would be to apply a topical anesthetic (Sarna, Prax, Benadryl) liberally and often on the areas when they itch, so you'll be better able to leave them alone. Sorry I can't be more specific.
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