The prevalence of DSM-III-R "prodromal" symptoms of schizophrenia in non-psychotic psychiatric outpatients.

A cross-sectional point prevalence study of the DSM-III-R prodromal symptoms in non-psychotic (n = 501) consecutive outpatients from a catchment area with 260000 inhabitants is presented. The relationship between the three most psychosis-specific prodromal symptoms and the development of psychosis during the following 6 months was also explored. The prevalence of any prodromal symptom was 25%, the most prevalent being impairment of role functioning (14%), isolation and withdrawal (11%) and lack of initiative (8%). The most prevalent symptom in affective disorders was lack of initiative (14%); in personality disorders, it was impairment of role functioning (21%). The prevalences of the most psychosis-specific symptoms "peculiar behaviour", "magical thinking" and "unusual perceptual experiences" was 1-2%. At re-evaluation 6 months later, three of 20 patients (15%) with one or more such symptoms had become psychotic, two with schizoaffective disorder, one with affective psychosis. It was concluded that DSM-III prodromal symptoms are common among non-psychotic outpatients, but most such symptoms are non-specific for psychosis. Persistent peculiar behaviour, magical thinking and unusual perceptual experiences have a very low prevalence but may indicate an increased risk for psychosis. Such patients should be followed with that risk in mind.