Basically, if you overlap dysthymia with bipolar, that's still bipolar, just with long periods of depression in between manic phases. Bipolar is over-diagnosed a lot currently, and one consideration is that if you are constantly depressed (dysthymia), then when you do ever get up to a normal mood level it feels like something is wrong, because you're not used to it and can't remember feeling good before. So that normal mood state can get misidentified as mania and you can get diagnosed with bipolar. I don' t know if that is the case for you or not. I would have to know more about what your manic states are like. Specifically, how destructive are they? I know that if I start approaching a normal energy level or positive mood, I tend to think that I'm getting a bit manic. I have had dysthymia since childhood also. I think that can come from being a vulnerable and sensitive child, and being exposed to change or instability without getting the support and validation that you need to work through it and adjust.