Why 
Because my friend had a spot on her leg about 2 mo. ago that looked like a lyme bite rash but she also had some spots and blisters elsewhere on her body that were determined by a "doc in the box" she saw while on vacation as poison oak.
At first I thought it could be the herald spot from pityryosis rosea and her other spots part of that...but some of her spots were blisters.
The doc in the box passed by the spot on her leg after saying, "that looks different"
and didn't refer to it again.
She was treated for the Poison Oak diagnosis with prednisone. Her spots all eventually went away but she recently looked at pics of initial lyme bite spot rashes and they look a lot like the spot that was on her leg.
In any case, she is having a test tomorrow just in case.