I tried to find some research for this but couldn't find anything! I was originally diagnosed manic/depressive (as a tween) but as an adult it read MDD, and hypomania. I've read that you can not be bipolar and have MDD but the term bipolar was never used with me, only hypomanic. Also, my hypomanic episodes aren't followed by depression, and my depression isn't lifted with hypomania. So... I really have no clue the mechanics of it all but it's a really good question!