Schizophrenia and Depression – Challenging the Paradigm of Two Separate Diseases

Abstract

Affective symptoms, depression in particular, show high rates in schizophrenia. When occurring in combination with subclinical psychotic symptoms they are precursors of psychosis risk. Their increase over time is associated with an increase in psychosis risk and their decrease with a fall therein. The prodromal stage of severe depression and the prepsychotic prodromal stage of schizophrenia show, in the mean, more or less identical symptoms, but are diagnostically distinguishable from each other only after the onset of psychotic symptoms. In the course of full-blown schizophrenia depressive mood is the most frequent symptom. even more frequent than the positive symptoms specific to schizophrenia. In psychotic relapse episodes depressive symptoms, too, increase and to some extent also decrease when the psychosis remits. 15-20% of the relapse episodes are characterised by affective symptoms without psychotic symptoms. Attempts to identify a depressive prodrome in psychotic relapses have not yielded consistent results. The Kraepelinian model of two discrete illness groups does not provide an adequate description of the functional association between affective and psychotic symptoms observable throughout the illness course. A model of schizophrenia based on symptom dimensions, which are in part functionally related and differ in their shares in individual illness, seems to be closer to reality. Since the currently available antipsychotic and antidepressant medications and specific psychotherapeutic techniques act on symptom dimensions rather than the Kraepelinian disease concepts, a dimensional model of schizophrenia seems more useful in therapeutic respect as well.