I don't believe it's ICH. You would notice it on the fins before the body. I wouldn't do anything too crazy just yet. Let it play out a bit, keep an eye on it. You don't want to be chasing down phantom diseases and end up causing the demise of the fish (that would be my fear).
It's too big to be ick plus from my experience tigs are pretty resilient against ich. I would just wait until it goes away on its own, if not and you want to try meds, I've had great results with PIMAFIX & MELAFIX (used simultaneously).