"That may very well be what happened. Are there any cures for demons? I assume Castiel already knows what it could be on your sphere." The curious thing is if there is any difference considering it happened here, but there are no demon possessions here as far as he can tell, so it's best to go with what makes sense for their sphere.

Istredd's really only asking out of interest and to offer Castiel sympathy later on, he has no intention of them getting involved outside of advice or compassion. This is not really their problem and they would only make it worse at this point, of that he feels sure.

Istredd has a great deal of emotional power over Lucifer which he is aware of. It's a double-edged blade and a two-way street. We know all the things to say to each other that would hurt the most. He squeezes his hand. So good thing neither of us is likely to be possessed by a demon.