The term “schizoaffective psychosis” was first introduced by Kasanin (1933) when he described a group of patients with good premorbid functioning who developed acute psychoses with a mixture of psychotic and affective symptoms, but fully recovered after a few months. While Kasanin is credited with introducing the term, it is defined differently now. Schizoaffective disorder is a complex illness whose definition has changed significantly over time. Despite the continued attempts to better define and classify schizoaffective disorder, much controversy and conflicting results remain. Unfortunately, schizoaffective disorders have been poorly investigated. Kahlbaum (1863) is usually considered the first psychiatrist in modern times to describe schizoaffective disorders as a separate group (Angst and Marneros, 2001). As Tsuang and Simpson (1984) reported, empirical findings are often contradictory and have at times supported the idea that schizoaffective disorder is (a) a variant of schizophrenia; (b) a variant of affective disorder; (c) a different and heterogeneous diagnostic group.
Regarding classification systems, in DSM-II schizoaffective disorder was included in the group of schizophrenic disorders, although some studies with controversial results were published (Procci, 1976; Harrow, 1984). While in DSM-III schizoaffective disorders had only the state of a remnant category, in DSM-III-R schizoaffective disorders were extended to a “true” entity with specific diagnostic criteria (Jäger et al., 2004).