Maybe it’s lingo that is used between psychiatrists in the field. Like the term “malignant narcissist”. I do not believe “malignant narcissist” can be found in the DSM. Personally, I have not heard of such a thing as atypical affective disorder. Maybe this means that this is an unusual, uncommon form of affective disorder. If this is the case, I would think this is more of a descriptor than a diagnosis. But then there is “atypical depression” being used as a diagnosis that comes with a specific set of symptoms.

FWIW