What's the opposite of major depressive disorder? Bipolar disorder, BD, involves manic episodes and depressive episodes.

If someone has a depressive episode, that person may have major depressive disorder, MDD or BD.

If someone has a manic episode, that person may have ___________ or BD.

So, what is the opposite of MDD?

It seems that "mania" is a term that describes an episode. So "mania" is the opposite of "depression" rather than "MDD".

Is there a major mania disorder? I have heard of kleptomania and pyromania which appear to be classified as impulse control disorders but nothing that appears to be analogous to major depressive disorder
There are two ways to interpret/answer this question. First, is there a recognized disorder that is characterized by mania in the absence of depression? Second, are there people who experience mania in the absence of depression?

The answer to the first interpretation is no. There is currently no "major manic disorder" or "unipolar mania." Given the DSM-5 criteria, a person with mania in the absence of depression would likely receive a diagnosis of Bipolar I Disorder, which is the same diagnosis that they would get if they had mania with depression.

The answer to the second interpretation is obviously more difficult. I don't have concrete data, but it appears to be rare. See the following link for an interesting discussion. 

Why no unipolar mania listing in DSM-IV?