Pervasive developmental disorders and psychosis.

Pervasive developmental disorders (PDDs) and infantile schizophrenia were initially thought to be the same condition, but distinct differences were described in later research. However, attempts to identify psychosis in individuals with PDDs continue to be challenging and controversial. The two disorders share many similar features, including perceptual abnormalities, thought disorder, catatonia, and deficiencies in reality testing. Progress has been made in describing features of PDDs that can be confused with psychosis and in surveying the prevalence of psychotic symptoms in populations with intellectual disability, although there are fewer data on PDD populations. Further research is needed on the longitudinal course of PDDs and the relationships with adult disorders such as psychosis and mood disorders. This research would not only improve the diagnosis and treatment of these complex disorders but would help to unravel the complex brain pathways involved in the perception of the external world that is central to psychosis and PDDs.