What is actually observed in so-called 'biplar children'? If you read the research reports carefully, they describe broad and persistent emotional dysregulation. Although these children have mood swings, they do not develop manic or hypomanic episodes. They are moody, irritable, oppositional and likely to misbehave—like all children with disruptive behavior disorders. Their grandiose thinking usually consists of little beyond boastfulness. No evidence from genetics, neurobiology, follow-up studies or treatment response shows that this syndrome has anything in common with classical bipolarity.
The categories used in psychiatric diagnosis are based on observation of signs and symptoms, rather than on pathological processes. One can make use of a few signs, such as facial expressions associated with depression or the flight of ideas associated with mania. But what clinicians mainly use for diagnosis are symptoms, the subject experiences reported by patients. Psychiatrists have little knowledge of the processes that lie behind these phenomena. Thus psychiatric diagnoses, with very few exceptions, are syndromes, not diseases.