When DSM IV TR schizophrenia and bipolar disorders are examined phenomenologically on a Schizo-Bipolar dimension, their distribution overlapped significantly. While disorders at the extreme end of the psychosis spectrum differed predictably across the Schizo-Bipolar dimension to reflect prototypic classifications of schizophrenia and bipolar disorder, no clear-cut discontinuity was evident between the adjacent categories. This suggests a non-categorical distribution of psychotic and affective elements among a population of seriously mentally ill research volunteers with a history of psychosis. Because the pathophysiology of psychosis remains obscure, and thus lacks biomarkers, genetic research into the disorder has usually taken clinical, phenomenologically defined entities as its starting point (Allen et al, 2009
). In considering disease risk, rather than overt illness categories, a dimensional approach to analyze schizo-bipolarity is therefore more likely to be very fruitful when examining endophenotypes and the genome. This conceptual approach is also consonant with the recently proposed NIMH Research Domain Criteria project (RDoCs; http://www.nimh.nih.gov/research-funding/rdoc.shtml
), that seeks new ways of classifying psychopathology cutting across disorders as traditionally defined, based on dimensions of observable behavior and neurobiological measures to be studied across multiple levels of analysis, from genes to neural circuits to behaviors. In fact, the Schizo-Bipolar scale was explicitly developed for use in the BSNIP study (Thaker 2008
), a multi-site study of psychotic disorders that gathers multiple biological measures in order to detect relationships between neurobiological and clinical variables.
To our knowledge no similar prior effort exists in representing the key diagnostic characteristics of psychotic disorders on a dimensional continuum between schizophrenia and psychotic bipolar disorders. The strengths of our approach lies in the assessment of cross-sectional and life-time information of bipolar and psychotic symptomatology in a large sample of these subjects in the same study. In our experience, the Schizo-Bipolar Scale is reliable, easy to use, and can be completed relatively quickly after a diagnostic interview complemented by informant interviews and chart reviews as needed. Limitations include the fact that comprehensive information about life-time affective and psychotic symptoms is at best an approximation, as it relies on autobiographical memory, and availability of adequate collateral and medical record information. However, it should be noted that our SBS ratings were based not only on SCID interviews, but often by reports from relatives also recruited into the study and reviews of chart notes when they were available. Also, all of this information was reviewed at a consensus diagnosis meeting where SBS scores were determined. Second, it is to be noted that this scale addressed the schizophrenia-bipolar continuum, and not the full psychotic disorder spectrum (by not including the psychotic depression patients); further work is needed to examine the spectrum from schizophrenia to major depression with psychosis as well as organic psychotic disorders more fully. Third, as currently developed, this scale uses only the psychosis and affective dimensions. Psychopathological dimensions such as symptomatology, such as mood congruent vs non- congruent delusions may also be relevant to the schizophrenia vs psychotic bipolar disorder distinction (ref); another aspect of symptomatology considered to be sufficient for dagnosis in DSM-IV criteria is bizarreness of delusions. We will consider incorporating these measures in the next iteration of the schizobipolar scale. However, the reliability of assessing these measures is debatable especially when reviewing past episodes of the iillness (Cermolacce et al 2010
; Kumazaki, 2011
More data are needed to examine the reliability and longitudinal stability of Schizo-Bipolar Scale ratings, and the extent to which scores on this scale might inform the etiopathological similarities and distinctions that may exist across the spectrum of psychotic disorders. Further work is likely to offer a useful clinical tool for the practicing clinician as the field moves toward a judicious combination of categorical and dimensional approaches to psychiatric classificatory systems.
Our results suggest that the depressive and bipolar subtypes of schizoaffective disorder may represent categorical captures of a continuous reality, supporting the case for schizoaffective disorder as an intermediate category, not weakening. A major question for the field is whether psychotic disorders should be categorized at all or whether a continuous dimensional representation is more appropriate. It may well be that like with blood pressures or resting blood sugars, we need to impose cutoffs on the dimensional realities to be able to address diagnosis and treatment.
Clearly, as in many aspects of psychiatric diagnosis, those favoring categorical and dimensional models (the lumpers and the splitters) have had differing views of psychotic disorders; this debate is a critical component of current thinking in DSM5 (www.dsm5.org
). Some recent studies suggest dimensional approaches do not necessarily offer better predictive power than categorical diagnoses (Moller et al 2011
). The results of the present study rather suggest in the words of Lewis Carroll that “all have won and all shall have prizes”. Many patients conformed to prototypic categorical diagnoses of schizophrenia or bipolar disorder, yet the percent of patients that did not fit neatly into those categories was also quite considerable. Thus, a hybrid conceptualization model is indicated with a high representation of cases with prototypic schizophrenia or bipolar disorder together with a large group of patients on the continuum between them. In this situation, forcing patients into one of the diagnoses of schizophrenia or bipolar disorder may often not be appropriate. Placing these non-prototypic patients on a continuum between the disorders may be appropriate using a strategy such as the Schizo-Bipolar Scale, indicating a need for studies addressing questions about treatment implications and about the neurobiological similarities of intermediate cases with those of the prototype disorders.