A Critical Overview of the Validity of the Current Concept of Bipolar Disorder

<b>Objectives</b>: The main aim was to evaluate the origin and empirical support of the current diagnostic criteria for (hypo)manic and depressive episodes in BD focusing on their nosological (i.e., is it a real entity?) and diagnostic validity (i.e., how well do the criteria for the category portray the entity?). <b>Methods</b>: A narrative review of relevant textbooks/reports and articles published in peer-reviewed English-language journals (from the online databases PubMed and PsycInfo), covering the period 1900-2024 and using the terms "validity" OR "diagnosis" AND "manic-depressive"; "mania"; "hypomania"; "depression"; and "melancholia" was performed. <b>Results</b>: Mania appears to be a valid construct in nosological terms, although its validity in the diagnostic domain requires further research. There are scant and controversial empirical data on the nosological validity of separating hypomania from mania as different episodes. The current concept of bipolar depression combines different forms of episodes (melancholic and non-melancholic, with or without psychosis, recurrent or not) without conclusive evidence that all of them are necessarily part of the illness (i.e., limited nosological validity). <b>Conclusions</b>: The validity of the current definition of BD is limited and should be the focus of future research. A valid definition of BD would improve our ability to understand the pathophysiological basis of the illness and contribute to more tailored therapeutic approaches.