I'm going to go out on a limb here, and ask if you have ever considered that he may have an attachment disorder?
NOT the extreme radical stuff, but rather, some form of insecure attachment... which can happen in kids with serious medical problems.
I haven't walked that road - the serious medical problems road - but we have had to "re-attach" with a kid who went off the rails due to un-diagnosed major problems... which of course there was no help for without knowing what the problem was.
If the problem is insecure attachment, the approach needs to be very, very different than trying to parent "defiance". Normal parenting techniques do not work.
