Looking for something very, VERY disturbing/uncomfortable.

I just watched American Psycho and heard that the book was even more disturbing and graphic. So now I’m curious and want to read something that takes it even further than that. I don’t particularly want it to just be pages on pages of descriptive mutilation – that just seems too easy? If that makes sense. Just like how in American Psycho, it it was just death scenes it wouldn’t be any good but all the nuances of the things he does outside (and including) killing just made you feel uncomfortable throughout. Doesn’t even need to be a specific genre. Any suggestions?