Psychotic depression (PD) is classified as a sybtype of severe depression in the current diagnostic manuals. Accordingly, it is a common conception that psychotic features in depression arise as a consequence of depressive severity.

To determine whether the severity of depression and psychosis correlate in accordance with the “severity-psychosis” hypothesis and to detect potential differences in clinical features of psychotic and non-psychotic depression (non-PD).

We aimed to answer the following questions:

1. Does the clinical profile differ between patients with PD and non-PD?

2. Is the severity of depression and psychosis correlated in patients with depression?

Quantitative analysis of Health of the Nation Outcome Scales (HoNOS) scores from all patients admitted to a Danish general psychiatric hospital between 2000 and 2010 due to a severe depressive episode.

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 (Spearman coefficient = 0.12).

The results suggest that the severity of depression is unlikely to be the key determinant for the development of psychosis and supports the hypothesis that the psychotic- and non-psychotic subtypes of depression are in fact distinct clinical syndromes.