The epidemiology of first-episode psychosis is poorly understood because of the paucity of systematic studies, yet it constitutes the fundamental basis for understanding the disorder and the foundations on which clinical, biological, therapeutic, and long-term outcome studies are built. A particular need is to clarify the diagnostic breadth of first-episode psychosis and, on this basis, to undertake systematic comparisons across representative populations of the psychoses, to include comparisons with first-episode mania. Considered here is the new generation of prospective studies that may be able to inform in some way on these issues. Attainment of the above goals requires prolonged accrual of "all" cases of nonaffective, affective, and any other psychotic illness, including first-episode mania, to derive the required representative populations. To illustrate some of the challenges, the structure of the Cavan-Monaghan prospective first episode study is described and its interim findings are outlined, as rural Ireland provides psychiatric care based on strict catchment areas and is characterized by substantive ethnic and socioeconomic homogeneity and stability. It is argued that there are 3 primary diagnostic nodes (schizophrenia spectrum psychosis, bipolar disorder, and major depressive disorder with psychotic features) around which there exist numerous additional, overlapping, and well-populated diagnostic categories that are distinct only in terms of their operational definition. Only through systematic, epidemiologically based studies that access this intrinsic diversity are we likely to understand fully the origins and pathobiology of first-episode psychosis.

No abstract

While recent research on psychotic illness has focussed on the nosological, clinical, and biological relationships between schizophrenia and bipolar disorder, little attention has been directed to the most common other psychotic diagnosis, major depressive disorder with psychotic features (MDDP). As this diagnostic category captures the confluence between dimensions of psychotic and affective psychopathology, it is of unappreciated heuristic potential to inform on the nature of psychotic illness. Therefore, the epidemiology and clinical characteristics of MDDP were compared with those of schizophrenia and bipolar disorder within the Cavan-Monaghan First Episode Psychosis Study (n = 370). Epidemiologically, the first psychotic episode of MDDP (n = 77) was uniformly distributed across the adult life span, while schizophrenia (n = 73) and bipolar disorder (n = 73) were primarily disorders of young adulthood; the incidence of MDDP, like bipolar disorder, did not differ between the sexes, while the incidence of schizophrenia was more common in males than in females. Clinically, MDDP was characterized by negative symptoms, executive dysfunction, neurological soft signs (NSS), premorbid intellectual function, premorbid adjustment, and quality of life similar to those for schizophrenia, while bipolar disorder was characterized by less prominent negative symptoms, executive dysfunction and NSS, and better quality of life. These findings suggest that what we currently categorize as MDDP may be more closely aligned with other psychotic diagnoses than has been considered previously. They indicate that differences in how psychosis is manifested vis-à-vis depression and mania may be quantitative rather than qualitative and occur within a dimensional space, rather than validating categorical distinctions.