I remember my first secondary syphilis diagnosis working in the county public health clinic. A guy came in with spots on his palms. No particularly risky history, at least that he related. It wasn't the first thing I thought of, but I told him I should check him for syphilis too along with the other things I was testing him for, even though I didn't think it was very likely. He was fine with that. First result to come back, he was rip-roaring positive on titres and we got him on Bicillin right away.
It'll fool you unless you're thinking about it. It's not the "Great Imitator" for nothing.