Cyclothymia.

Over the last three decades, cyclothymia has been positioned in one of two principal ways: formally classified as a mood disorder, and less formally categorized at a "cyclothymic temperament" (CT) level. This review considers its historic evolution and provides five models for conceptualizing independence or interdependence between cyclothymia as a temperament style and as a formal mood disorder. Findings argue for CT to be conceded and appropriately defined. Secondly, it is recommended that cyclothymia's expression as a mood disorder should be positioned within the bipolar II disorder class-albeit perhaps having briefer mood swings and fewer episodes, more rapid cycling, and greater reactivity to environmental factors than is conceptualized currently for bipolar II disorders. By allowing cyclothymia both axis I and axis II status (although necessitating differing terminology), research evaluating any shared biological underpinnings and any predisposition provided by the CT temperament style to a later formalized bipolar II condition would be advanced.