Although clinical descriptions of mixed states date from the beginning of the 19th century, the first use of the term mixed state dates back to French nosological descriptions by Falret in 1861, who thus described "predominant ideas often of a sad nature, in the middle of a state of excitement simulating true mania", but also "inverse states, an extreme confusion of ideas which is combined with the calm of movements and the appearance of reason". It is rather in Germany that the mixed state will be integrated into a homogeneous conception of a psychiatric disorder, similar to our modern conception. Kraepelin describes it more completely in the seventh edition of his treatise. Weygandt, a student of Kraepelin, contributed to the description of mixed states and wrote a treatise specifically on this subject. Kraepelin's conception will be expanded by differentiating on the one hand the transitional forms (the mixed state being a form of passage between the manic and depressive poles) and the autonomous forms (with a worse prognosis). Akiskal offers an interesting enrichment of Kraepelinian and Hamburgers in mixed states. To do this, he uses his work on temperaments. Some clarification therefore seems necessary on the notions of temperament, character, and personality before delving deeper into this data. A decisive synthesis work is carried out by McElroy, et al. whose objective is then to establish an exhaustive review concerning the clinical characteristics, demographic, evolutionary, biological, familial, comorbidity, or response therapy of mixed states. Mixed states appear today in international classifications and are defined there as the summation of manic and major depressive episodes, both complete. Considering these definitions as too restrictive, some authors propose other broader and very variable criteria.
