I've had the idea before seeing the concept art Reav3 post on his recent Champion Roadmap blog, but after seeing it, I'm really thinking Urgot is going to have some type of incurable disease.
If you take a good look at the guy in the take in the background (likely Urgot) you can see that his arm is pretty misshapen. And if you look at what I think is his head, that also appears to be a little deformed (though maybe less so than his arm). So I think the disease Urgot has, will be something like a cross between Elephant Disease and Bubonic Plague; where his flesh is heavily deformed by both massive and numerous tumors, and decay. Additionally, he could have a bunch of scars showing where the more life threatening tumors have been removed. I think this would add quite a bit to Urgot being this horrifying monstrosity, combined with chemical filled tubes running in and out of his body.
WARNING: If you want to look up Elephant Disease and Bubonic Plague on google images, just know that theses diseases can be quite horrifying and disgusting to look at.