• A recent clinical study that compared patients with DSM-III-R major depressive disorder with psychotic features to those without psychotic features (13) reported that the delusional patients were younger, more frequently had a previous history of delusions and more frequently had feelings of worthlessness.

• Another study did not find differences between psychotic and non-psychotic depressed subjects in their clinical features (age of onset, duration of the episode, frequency) (14).

Our study reports on the prevalence of DSM-IV major depressive episodes with and without psychotic features in the general population of five major western European countries.

• which depressive symptoms were more likely to be associated with psychotic features in the general population

• and the relative contributions of age, gender and chronicity.

The participants in the five countries were interviewed by telephone with the broader purpose of investigating sleep habits, sleep-related symptoms, and psychiatric and sleep disorders.

The target population was all non-institutionalized residents ages 15 years or over.

• In the first stage, the population was divided according to its geographical distribution as per the official census data for each country,

• then telephone numbers were randomly drawn. In the second stage, within each household a member was selected as a function of age and gender using the Kish method (16) in order to maintain the representation of the sample and to avoid bias related to non-coverage error.

We excluded potential participants who had insufficient fluency in the national language, who had a hearing or speech impairment or with an illness that precluded the feasibility of an interview.

The participation rate was:

• 79.6% (4,972 of 6,249 eligible individuals) in the UK;

• 68.1% (4,115 of 6,047 eligible individuals) in Germany;

• 89.4% (3,970 of 4,442 eligible individuals) in Italy;

• 83% (1,858 of 2,234 eligible subjects) in Portugal;

• and 87.5% (4,065 of 4,648 eligible individuals) in Spain.

Overall, 18,980 subjects participated in the study.

The overall participation rate was 80.4%.

This sample is representative of 205,890,882 inhabitants.

Prevalence

The current prevalence of DSM-IV major depressive episode was set at 2.4% in this sample.

About 19% of these subjects with a major depressive episode had psychotic features yielding a prevalence of major depressive episodes with psychotic features of 0.4% in this sample.
Thus, psychotic major depression is a relatively common disorder affecting four out of 1000 individuals.

Severity and Psychotic Features

Surprisingly, although the severity of the depression is an important issue for the presence of psychotic features, we found a considerable number of subjects with mild or moderate major depressive episodes who had psychotic features and other subjects who did not have enough depressive symptoms to fulfill the criteria for a major depressive disorder.

 As many as 10% of subjects with two depressive symptoms had psychotic features.

This association cannot be fully explained by the presence of a bipolar disorder or another psychotic disorder: these two disorders accounted for 34% of the association.

Other mental and neurological associations

Several other mental and neurological disorders were associated with psychotic features in subjects who had depressive symptoms but did not meet all the criteria for a major depressive episode.

Namely, we found many subjects who had:

• obsessive compulsive disorder,

• post-traumatic stress disorder,

• panic attacks,

• history of abuse of alcohol.

In non-depressed subjects who had psychotic features, an identifiable mental or neurological disorder was found in at least 60% of cases.

Depressive symptoms associated with Psychotic Features

When examining individual depressive symptoms, we found that subjects who reported feelings of worthlessness or guilt were the most likely to have psychotic features, confirming the results in a recent clinical study (13).

However, the severity of this symptom was not related to the presence of psychotic features.

Guilt may be a useful cue to delve more deeply into the presence of psychotic features.

Characteristics of Depression with Psychotic Features

We also found that subjects with a major depressive episode with psychotic features were more likely to have consulted in the past for depression, suggesting a possible recurrence of the disorder.

They had also a longer duration of the major depressive episode than the subjects without psychotic features.

This is in line with findings reported in clinical studies where patients with a major depressive episode with psychotic features are more likely to have recurrent depressive episodes, and episodes of longer duration (10-13).

These data suggest the duration of episode may increase the risk of developing, delusions, perhaps through a biologically based process.

However, we did not find that psychotic features were associated with younger age as suggested by another study (13).

This has a double impact, namely, on patients diagnosis identification and on treatment.

Contrary to a common belief, depression with psychotic features is not associated with severity.

This last point raises the prospect that these patients are seen by general practitioners and remain inadequately treated.