Conceptualizing psychotic disorders: don't throw the baby out with the bathwater
Authors: Rajiv Tandon
Journal: World Psychiatry (2016)

“Everything should be made as simple as possible, but not simpler.” (A. Einstein) Since its introduction two centuries ago, the term “psychosis” has been conceptualized in a variety of ways, but is generally defined by impaired reality testing characterized by delusions, hallucinations and/or disordered thinking. There are several limitations in our current conceptualization of psychoses1, including: a) unclear boundaries between disorders (e.g., between psychotic bipolar disorder, schizoaffective disorder and schizophrenia); b) enormous unexplained clinical heterogeneity within individual psychotic disorders; c) the frequent co-occurrence of mood and psychotic symptoms; and d) poorly described relationships between subclinical psychotic phenomena in the general population and defined psychotic disorders. In an effort to address these challenges, van Os and Reininghaus2 synthesize findings from various fields and propose that psychosis is best conceptualized as a continuous phenotype that includes subclinical psychotic-like experiences in the general population (extended phenotype) and is continuous across the Kraepelinian dichotomy (transdiagnostic phenotype), and that this transdiagnostic continuity is seen at both clinical and subclinical levels. They claim further support for their proposition by citing shared etiological factors (most notably childhood trauma) across this transdiagnostic, extended phenotype. A careful scrutiny of the tenets of their hypothesis and its implications is warranted. There are three premises on which this hypothesis rests: a) psychosis-like experiences in the general population are analogous to and both phenomenologically and temporally continuous with true psychotic phenomena in individuals with a defined psychotic disorder; b) since psychotic symptoms co-vary with depression and anxiety symptoms in both clinical and general populations, they represent a single phenotype; and c) there are shared etiological factors across the breadth of the extended, transdiagnostic phenotype, thereby validating it. Each one of these postulates is based on an uncritical reading of the literature. The assertion that psychosis-like phenomena detected in the general population are similar to psychotic experiences in the clinical setting ignores distinctions between imagery and hallucinations, or between overvalued ideas and delusions. This premise is further undermined by the fact that data in the general population are generally collected by inexperienced interviewers using imprecise instruments such as the Composite International Diagnostic Interview (CIDI)3. Using the CIDI to reliably evaluate depression in the general population is similarly problematic4. Jumping to the conclusion that cooccurrence of mood and psychotic symptoms across a range of psychiatric disorders implies that all these disorders are part of a singular “general psychosis syndrome” is unwarranted and runs counter to the vast amounts of data indicating the utility of current diagnostic categories. Furthermore, the authors ignore their own note of caution5 that “evidence on a general psychosis dimension remains restricted to the here studied schizophrenia spectrum disorders” and that “we did not find evidence that would justify replacing specific diagnostic constructs of psychosis with a general psychosis syndrome”. The assertion about etiological factors being common across the breadth and depth of the extended transdiagnostic phenotype rests on an overly selective citation of the literature. For example, genetic risk for schizophrenia is poorly correlated with psychosis-like experiences in the general population7. Also, sharing some risk factors does not denote a singular clinical entity. As noted by one of the authors8, there was a significant effort in the development of DSM-5 to address the limitations in our current characterization of psychotic disorders. Relevant revisions in DSM-5 include the elimination of the classic subtypes of schizophrenia9, the addition of unique psychopathological dimensions10, the provision of a scale to measure each of these dimensions across all psychotic disorders, a more precise definition of the boundary between schizophrenia and schizoaffective disorder, and the addition of a new category of “attenuated psychosis syndrome” as a condition for further study in Section 3 of the manual11. There was, in fact, a vigorous debate among members of the Psychotic Disorders Work Group about the merits of including a “general psychosis syndrome” in DSM-5, and a substantial majority found an insufficient basis to do so. The group recognized that there are individuals in the general population who exhibit subclinical psychotic or psychosis-like symptoms and that a subset of these individuals is at high risk of developing a psychotic disorder. A definition of attenuated psychosis syndrome was found to best define this group at “substantially higher risk”, and data continue to support the validity and utility of this construct6. In line with the multi-dimensional nature of psychotic disorders5,8,9, the most important change in DSM-5 was the delineation of distinct symptom domains across all psychotic disorders: reality distortion (delusions, hallucinations), negative symptoms, disorganization, cognitive impairment, motor symptoms (e.g., catatonia), and mood symptoms (depression, mania). Measuring the relative severity of these symptom dimensions through the course of illness in the context of treatment can provide useful information to the clinician about the nature of the illness in a particular patient and in assessing the specific impact of treatment on different aspects of the patient's illness. A 0-4 rating scale with anchor points for each of the eight items (delusions, hallucinations, negative symptoms, cognitive impairments, disorganization, catatonia, depression, and mania) to rate these six dimensions is provided in Section 3 of the DSM-5 manual. As a simple rating scale, it should encourage clinicians to explicitly assess and track changes in the severity of these dimensions in each patient with schizophrenia and use this information to guide measurement-based, collaborative treatment. The article by van Os and Reininghaus prompts a critical re-examination of our conceptualization of psychotic disorders. The specific premises and implications of their model of “psychosis as a transdiagnostic and extended phenotype in the general population”, however, do not stand up to scrutiny. While our current construct of the psychosis syndrome is inadequate, we do not want to throw the baby out with the bathwater. Replacing an imperfect but useful construct with one that is more flawed and less valid is a retrograde step12. Changes in DSM-5 (revisions in ICD-11 are likely to be similar) appear to represent our best foot forward: they enhance clinical utility while providing a more useful platform in integrating emerging genetic and other neurobiological information. Rajiv Tandon University of Florida, Gainesville, FL, USA