Objective: Difficulties surrounding the classification of mixed psychotic and affective syndromes continue to plague psychiatric nosology. This paper addresses the controversy regarding the diagnostic validity of schizoaffective disorder (SAD), a diagnosis that is used in both DSM-IV and ICD-10 and one that encroaches on both schizophrenia (SCZ) and bipolar disorder (BD). Methods: A systematic synthesis of clinical and empirical literature, including evidence from cognitive, neurobiological, genetic, and epidemiological research, was undertaken with the aim of evaluating the utility of the SAD classification. Results: Distinctions between the diagnostic categories of SCZ, SAD and BD are not clearly demarcated by findings from neuropsychological, neuroimaging, molecular neurobiology, or genetic epidemiology studies. On the contrary, convergent evidence purports overlap across current diagnostic boundaries in the heritability and pathophysiology of psychotic and affective disorders. However, there are some disorder-specific findings. Conclusions: Schizoaffective disorder is a prototypic boundary condition that epitomizes the pitfalls of the current categorical classification system. Future revisions to the DSM should consider the implementation of one of two alternative models to account for individuals presenting with mixed psychotic and affective symptoms. These include the views that (i) SAD is a comorbid set of symptoms that occur as a by-product of two separate disorders (SCZ and BD) or, that (ii) SAD exists as the mid-point on a continuum between SCZ and BD, such that the incorporation of these two disorders onto one dimension may be a suitable alternative. Hence the category SAD should be omitted in future revisions of DSM, allowing the development of meaningful nomenclature that rests upon further rigorous investigation of differences and similarities between disorders.
- Bipolar disorder