Logic and justification for dimensional assessment of symptoms and related clinical phenomena in psychosis: relevance to DSM-5.

Work on the causes and treatment of schizophrenia and other psychotic disorders has long recognized the heterogeneity of the symptoms that can be displayed by individuals with these illnesses. Further, researchers have increasingly emphasized the ways in which the severity of different symptoms of this illness can vary across individuals, and have provided evidence that the severity of such symptoms can predict other important aspects of the illness, such as the degree of cognitive and/or neurobiological deficits. Additionally, research has increasingly emphasized that the boundaries between nosological entities may not be categorical and that the comorbidity of disorders may reflect impairments in common dimensions of genetic variation, human behavior and neurobiological function. As such, it is critical to focus on a dimensional approach to the assessment of symptoms and clinically relevant phenomena in psychosis, so as to increase attention to and understanding of the causes and consequences of such variation. In the current article, we review the logic and justification for including dimensional assessment of clinical symptoms in the evaluation of psychosis in the Fifth Edition of the Diagnostic and Statistical Manual for Mental Disorders (DSM-5).