I subscribe to the kindling theory myself, mainly because my own bipolar illness seems to have intensified over time. Every episode I've had has seemed to lead to worse ones down the line. As for burning out, I've heard that but don't take much stock in it, although I have taken care of old people with bipolar and it's hard to tell what's BP from what's dementia, or simply an aspect of their personality. It's all interesting, and amazingly hard to prove one way or the other.