a1 Maryland Psychiatric Research Center, University of Maryland School of Medicine, and the Mental Illness Research, Education and Clinical Center, VISN 5 Veterans Administration, Baltimore, MD, USA
a2 Department of Psychiatry, University of New Mexico School of Medicine, Albuquerque, NM, USA
a3 Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands
a4 Division of Psychological Medicine, Institute of Psychiatry, London, UK
a5 Departments of Psychology and Psychiatry, Washington University in St Louis, St Louis, MO, USA
a6 School of Psychiatry, Black Dog Institute, University of New South Wales, Sydney, Australia
Background In an effort to group mental disorders on the basis of etiology, five clusters have been proposed. Here we consider the validity of the cluster comprising selected psychotic and related disorders.
Method A group of diagnostic entities classified under schizophrenia and other psychotic disorders in DSM-IV-TR were assigned to this cluster and the bordering disorders, bipolar (BD) and schizotypal personality disorders (SPD), were included. We then reviewed the literature in relation to 11 validating criteria proposed by the DSM-V Task Force Study Group.
Results Relevant comparisons on the 11 spectrum criteria are rare for the included disorders except for schizophrenia and the two border conditions, BD and SPD. The core psychosis group is congruent at the level of shared psychotic psychopathology and response to antipsychotic medication. BD and SPD are exceptions in that psychosis is not typical in BD-II disorder and frank psychosis is excluded in SPD. There is modest similarity between schizophrenia and BD relating to risk factors, neural substrates, cognition and endophenotypes, but key differences are noted. There is greater support for a spectrum relationship of SPD and schizophrenia. Antecedent temperament, an important validator for other groupings, has received little empirical study in the various psychotic disorders.
Conclusions The DSM-IV-TR grouping of psychotic disorders is supported by tradition and shared psychopathology, but few data exist across these diagnoses relating to the 11 spectrum criteria. The case for including BD is modest, and the relationship of BD to other mood disorders is addressed elsewhere. Evidence is stronger for inclusion of SPD, but the relationship with other personality disorders along the 11 criteria is not addressed and the absence of psychosis presents a conceptual problem. There are no data along the 11 spectrum criteria that are decisive for a cluster based on etiology, and inclusion of BD and SPD is questionable.
(Received May 22 2008)
(Revised April 07 2009)
(Accepted May 12 2009)
(Online publication October 01 2009)