Instrumental psychosis: the Good Soldier Svejk syndrome.

The possession of severe mental illness, mainly schizophrenia and affective psychosis, may be perceived in positive terms. We have identified a group of patients, most of them with a history of previous psychotic disorder, who present with deliberately created symptoms and behaviour, and who are defined as having instrumental psychosis. Because most such patients have had a psychotic disorder in the past the symptoms are very like those of a real psychosis. A parallel is drawn with the fictional anti-hero of the Czech nation, the Good Soldier Svejk, who demonstrated both real and instrumental psychosis. A rating scale, the 'pseudopsychosis inventory', was devised to identify the main components of this disorder and was applied in 15 consecutive patients presenting with putative psychotic disorders in whom assessment could be made by two raters within five days. The inter-rater reliability of the items of the scale was good (intra-class correlation coefficient 0.68). An epidemiological study with this scale in 45 patients with a putative psychotic disorder suggested the presence of instrumental psychosis in 2.