>>24610703 (OP)
Frisk by Dennis Cooper would appeal to you. Really intense. Gay couple experiment with extreme sex and one goes off the deep end. I haven't read his other works, but he's generally interesting in extreme homosexual relationships. The Sluts might be another good read, but I think I've read snippets online made up of ficticious extreme BDSM ads.
Another other thing I read around the same time as Frisk and was disturbing like that was In the Miso Soup, but that's more just a thriller and doesn't tread the same ground. Guy gets wrapped up in a serial killer's spree. Still pretty striking at times, and impressed me for the fact that it was just a thriller at its core.
The Necrophiliac by Wittkop felt almost like a Lolita for corpse-lovers to me, in concept. But I wouldn't describe it as so disturbing.
The Tunnel is disturbing at times, but it's a doorstopper, so you're in for much more than that. It's an incredible book if you want to tackle the whole thing, and I don't think reading excerpts alone would ever be worth it, but it was the chapter called Child Abuse that really struck me for how I felt carried away with the narrator's emotions (and this ties into some of the themes of the novel). Nothing really graphic here though, just a bitter history professor's life story as he becomes more and more self-involved.
I realised I'm just regurgitating what I read from pic related, but it's not really a thematically cohesive chart.
The Story of the Eye might appeal to you, but it's nothing extreme for someone used to the modern grotesque.
Haven't read Hogg but I've seen it bashed on here sometimes for in effect being gruesome pornography and little else.
Not on the chart is Fires on the Plain by Shohei Ooka. Liked that one quite a lot. Japanese solider on the retreat on a pacific island, being pushed to the extreme through delirium.
American Psycho is an obvious one if you haven't read it already.
Anyway, Dennis Cooper probably does what you're looking for.
