Controversies of mixed states in bipolar disorder: From Wilhelm Weygandt's contributions to DSM 5 classifications

The concept of mood disorders with mixed features, where both manic and depressive symptoms coexist, has been central to the development of the concept of bipolar disorder. This notion, which makes it possible to understand the simultaneity of apparently opposite states, was explored by Wilhelm Weygandt in his seminal work Über die Mischzustände des manisch-depressiven Irreseins (1899). Weygandt, who worked alongside Emil Kraepelin at the Heidelberg Psychiatric Clinic, published this monograph in the same year that Kraepelin consolidated his theory of manic-depressive insanity, marking a significant advance in the understanding of mixed disease states. Weygandt introduced the idea of a polarity shift as the foundation of mixed states, describing how affectivity, psychomotor activity and thought interact in a complex way, with no clear hierarchy between them. This approach, which remains highly relevant, challenges modern classifications, such as the DSM 5, by proposing a comprehensive view of mood disorders that considers the dynamic interactions of all affected areas. Although less recognized than Kraepelin's, Weygandt's work played a crucial role in crystallizing the theory of mixed states, the impact of which endures in contemporary psychiatry.