The validity of the severity-psychosis hypothesis in depression

Background: Psychotic depression (PD) is classified as a subtype of severe depression in the current diagnostic manuals. Accordingly, it is a common conception among psychiatrists that psychotic features in depression arise as a consequence of depressive severity. The aim of this study was to determine whether the severity of depressive and psychotic symptoms correlate in accordance with this severity-psychosis hypothesis and to detect potential differences in the clinical features of PD and non-psychotic depression (non-PD). Methods: Quantitative analysis of Health of the Nation Outcome Scales (HoNOS) scores from all patients admitted to a Danish general psychiatric hospital due to a severe depressive episode in the period between 2000 and 2010 was performed. Results: A total of 357 patients with severe depression, of which 125 (35%) were of the psychotic subtype, formed the study sample. Mean HoNOS scores at admission differed significantly between patients with non-PD and PD on the items hallucinations and delusions (non-PD = 0.33 vs. PD = 1.37, p<0.001), aggression (non-PD = 0.20 vs. PD = 0.36, p = 0.044) and on the total score (non-PD = 10.55 vs. PD = 11.87, p = 0.024). The HoNOS scores on the two items depression and hallucinations and delusions were very weakly correlated. Limitations: Diagnoses were based on normal clinical practice and not formalized research criteria. Conclusions: The symptomatology of PD and non-PD differs beyond the mere psychosis. Furthermore, severity ratings of depressive and psychotic symptoms are very weakly correlated. These findings offer further support to the hypothesis stating that the psychotic- and non-psychotic subtypes of depression may in fact be distinct clinical syndromes. (C) 2012 Elsevier B.V. All rights reserved.