Fig. 1

Schematic illustrating approaches to classifying bipolar disorder. The top panel illustrates the perspective taken by Tondo and colleagues, wherein they acknowledge that a dimensional perspective reflects clinical reality, but within this entity, subcategories have been created and labelled as bipolar I and II. The problem with this approach is that the boundaries of these subtypes are unclear and difficult to define. The bottom panel depicts our model in which bipolar disorder is a single entity comprising symptoms that vary according to severity and duration. In addition, the lower boundary of bipolar disorder in terms of duration of symptoms is a minimum of 2 days, and once the threshold of a manic episode has been reached, then the syndrome can be specified by simply indicating the number of days of manic symptoms the patient has experienced. In this way, treatment can be tailored to the individual’s symptoms and severity and impact of these symptoms. *Other-specified refers to the ‘Short-duration hypomanic episodes (2–3 days) and major depressive episodes’ diagnosis listed within the ‘Other-specified and Related Disorders’ category in DSM-5