How can you tell the difference between inverse psoriasis of the groin vs jock itch? my dermatologist isnt sure, it came on in a manner more implying jock itch but thinks it looks like psoriasis based on severity, (its had 5 years to spread though?

Since the treatments for these disorders differ significantly, I'd think a therapeutic trial of one or the other would offer a clue to diagnosis. Jock itch would respond to something like mycolog ointment while psoriasis wouldn't. You could also obtain a 2nd opinion from a dermatologist at the department of dermatology at a university hospital near you.