The challenge of describing schizoaffective disorder within a psychiatric nosology that requires categorical distinctions between diagnostic entities is substantial. Using a categorical diagnostic approach, the data reviewed herein suggests that schizoaffective disorder can be argued with nearly equal merit to be a variant of either schizophrenia or a mood (and particularly bipolar) disorder, a condition in which schizophrenia and a mood disorder are co-morbid, or a unique psychiatric disorder. This conclusion, however unsatisfying, appears to be unavoidable if a categorical approach to psychiatric diagnosis is undertaken. Moreover, the present review suggests that the challenges schizoaffective disorder presents to categorical psychiatric diagnosis are not unique to this condition, but are instead pervasive in psychiatric research and practice. Although most studies begin with the premise that schizophrenia and bipolar disorder are distinct conditions, the observation of minor mood disturbances among persons with the former and often severe psychosis among those with the latter should raise concerns about the certainty of clear diagnostic boundaries between them. The consistent observation of neuroimaging, electrophysiologic, neurochemical, neuroendocrine, genetic, and treatment findings that more effectively follow psychiatric symptoms rather than categorical diagnoses suggests that the former, and not the latter, may be the more useful focus of both psychiatric research and clinical practice.
Indeed, the present review suggests that the study, evaluation, and treatment of persons with psychiatric disorder is likely to be most productive when anchored to the dimensions of neurobehavioral dysfunction with which they present. This approach, which derives from the approach used in behavioral neurology and neuropsychiatry, begins with the premise that cognition, emotion, behavior, and sensorimotor function are distinct but interrelated domains of neurobehavioral function (Arciniegas and Kaufer 2006
). Regardless of the clinical condition (eg, stroke, trauma, neurodegenerative disease, idiopathic psychiatric illness) producing disturbances in these neurobehavioral domains, it is posited that their neuroanatomic and neurochemical bases are likely to be similar despite differences in the conditions disturbing brain structure and function. It is further suggested that there may be etiology-specific neuroanatomic, neurochemical, neuroendocrine, or genetic features of the condition producing neurobehavioral disturbances that are potential modifiers of their expression, persistence, and/or treatment-response. While bearing these modifiers in mind, the study, evaluation, and treatment of persons with neurobehavioral disturbances is then organized according to the dimension(s) of neurobehavioral function in which such disturbances are expressed.
It is our assertion that this approach is particularly well-applied to the study, evaluation, and treatment of schizoaffective disorder. This condition reflects aberrations in the distributed neural networks serving both information processing (ie, perception, information interpretation) and emotional regulation, among other possible dimensions of disordered neurobehavioral function, in persons whose presentations are currently described as ‘schizoaffective’. It is conceivable that other factors, including genetic and epigenetic variations and environmental contributors, may influence the expression of disturbances in information processing and emotional regulation domains, and that such factors may weigh particularly heavily on one rather than the other. In such circumstances, the presentation would be one that appears to be predominated by either psychotic or mood disturbances rather than by both. Directing the study, evaluation, and treatment at the core disturbances in information processing and/or emotional regulation, regardless of how these disturbances direct assignment of categorical psychiatric disorder, it is likely that a more coherent description of the relevant neurobiology and effective treatments would emerge. By extension, application of this neuropsychiatric approach to other psychiatric disorders may facilitate their study, evaluation, and treatment and also avoid the vagaries entailed by a psychiatric nosology predicated on categorical, and ultimately arbitrary, diagnoses.