Have you had time to research Grover's Disease or Transient Acantholytic Dermatosis, a torso specific rash (rare cases migrating to arms and legs). Few derms can recognize as it is less common and incorrectly treat it as Contact or Allergic Contact Dermatitis. My first outbreak lasted 1 year, this is normal, subsequent ones not as long lasting. I also had a biopsy done for it, but success of biopsy is based on a short window, must be in the active break out stage, mine had been broken out for 5 months already and was negative. Derm and I still have no doubt it is GD/TAD as I have all the other criteria in my history, exception being that more males get this than women.