Numerous diagnostic categories exist that can be used to order and summarize the various manifestations of psychosis. Although these categories are meant to refer to broadly defined psychopathological syndromes rather than biologically defined diseases that exist in nature, inevitably they undergo a process of reification and come to be perceived by many as natural disease entities, the diagnosis of which has absolute meaning in terms of causes, treatment, and outcome as well as required sampling frame for scientific research. Conceived originally to bring order and facilitate scientific progress, they were important in establishing communication about psychiatric entities. But, they may also confuse the field by imposing arbitrary boundaries in genetic and treatment research and classifying patients into categories that upon closer examination have little to offer in terms of diagnostic specificity.

Given the fact that we have not yet discovered the natural boundaries of psychosis, but only observe its properties, the only way to achieve progress is to periodically reassess all the evidence in the hope of catching a glimpse of its natural pathology. This special issue of Schizophrenia Bulletin is the result of such an endeavor and was carried out in the context of Diagnostic and Statistical Manual of Mental Disorders (DSM)-V. “Deconstructing Psychosis” was the fifth diagnosis-related research planning session convened under the conference series on the “Future of Psychiatric Diagnosis: Refining the Research Agenda” and was held at American Psychiatric Association (APA) headquarters in Arlington, Virginia, on February 16 and 17, 2006. APA's American Psychiatric Institute for Research and Education sponsored the project in collaboration with the World Health Organization and the funding agency, the National Institutes of Health. The 5-year effort represents an unprecedented scientific preparatory phase in advance of the next revision of the DSM-V and other psychiatric classification systems.

A representative group of 21 scientists and clinicians from all over the world were approached with the task of helping to “deconstruct psychosis.” They were asked to summarize the evidence from their respective fields relevant for the diagnosis of psychotic disorders, in particular with regard to syndromes currently referred to as schizophrenia, bipolar disorder, major depressive psychosis, and substance-induced psychosis. For each field, a presenter was asked to summarize the evidence, followed by an assessment of this evidence by a debater. Participants were asked to examine their respective fields for evidence regarding the natural occurrence of the psychosis phenotype, as well as evidence relevant for the validity and usefulness of diagnostic constructs.

The actual process of “deconstruction” was conceived as follows. First, the processing of scientific and clinical evidence was stratified by area comprising genetics, psychopathology, cognitive psychology and neuropsychology, epidemiology, neuroimaging, neuropharmacology, postmortem research, transcultural research, early intervention, developmental epidemiology, and addiction, with presenters and debaters in each field. Second, participants were encouraged to assess the evidence in relation to both categorical and dimensional representations of psychosis and in relation to both clinical and subclinical expressions of psychosis.

Because research with a specific focus on diagnosis per se currently is rare; the participants adopted the strategy of examining the general research evidence and making specific translations to diagnostic validity and diagnostic practice. For example, comparable neuroimaging studies have been conducted in bipolar disorder and schizophrenia, yielding suggestions of both similarities and divergence. While these findings regarding group differences are relevant with regard to the validity of diagnostic categories, they are a very long way from being relevant for the actual diagnostic process in a single patient. The aim of Deconstructing Psychosis, therefore, was not to provide quick recommendations of which criteria to use for which categories in DSM-V. Rather, it attempted to assess to what degree current diagnostic practice is in agreement with data gathered in clinical and basic research; moreover, it intended to recommend which areas appear most promising for bridging the gap between current diagnostic practice and the natural phenotype of psychosis. It is hoped that the dissemination of this effort will contribute to more research in the area of diagnosis in psychotic disorders. Although our diagnostic classification systems are reliable and useful, they have limited validity in defining biological entities because these are unknown for most mental illnesses. This existence of diagnostic labels with limited validity in psychiatry needs to be tackled and improved with each subsequent version of our diagnostic systems.