Differential typology of delusions in major depression and schizophrenia. A critique to the unitary concept of ‘psychosis’

It is a current trend in psychiatry to discard the Kraepelinian dichotomy schizophrenia vs. manic-depressive illness and use the overinclusive label ‘psychosis’ to broadly indicate the whole spectrum of severe mental disorders. In this paper we show that the characteristics of psychotic symptoms vary across different diagnostic categories. We compare delusions in schizophrenia and major depression and demonstrate how these phenomena radically differ under these two psychopathological conditions. The identification of specific types of delusions is principally achieved through the differential description of subjective experiences. We will use two general domains to differentiate schizophrenic and depressive delusions, namely the intrinsic and extrinsic features of these phenomena. Intrinsic features are the form and content of delusions, extrinsic ones include the background from which delusions arise, that is, changes in the field of experience, background feelings, ontological framework of experience, and existential orientation. This kind of systematic exploration of the patients’ experience may provide a useful integration to the standard symptom-based approach and can be used to establish a differential typology of the clinical manifestation of psychosis based on the fundamental alterations of the structures of subjectivity characterizing each mental disorder, particularly with respect to the Kraepelinian dichotomy schizophrenic vs. manic-depressive illness.