Pediatric bipolar disorder: why the epidemic?

I am asked (this time as part of the post-quiz on a continuing medical education [CME] program): "A 17-year-old junior from the local high school is brought to you for an assessment because she won't tell her parents where she is spending her nights instead of coming home. The parents say she has been oppositional for months, irritable and has mood swings...A diagnosis of bipolar disorder is made..."

Wait! I thought that would be the quiz question! I thought the vignette would end with: "What diagnoses should you consider?" And the choices would be:

a. conduct disorder
b. substance use disorder
c. oppositional defiant disorder
d. parent-child relational problem

How in the world did we get to the point where an irritable teenager with mood swings and a crummy relationship with her folks is presumed to have bipolar disorder? It wasn't that long ago that it would have been presumed to be normal behavior. Geez...

Actually, it's been almost five years since Dr Angell provided this insight which is easily applied to understanding why there is an epidemic of childhood bipolar disorder, at least on CME quizzes.