Schizophrenia and related disorders: experience with current diagnostic systems.

Schizophrenia and related disorders include a variety of psychotic disorders in the major classification systems, ICD-10 and DSM-IV, with only partial concordance between the two systems. They both rely on demonstrated reliability, but which disorders are the most valid still has to be determined. Particularly for the ICD-10 disorders, only few studies examining external validity have appeared. Disorders of uncertain validity include 'schizo-affective disorders' which in ICD-10 contain the DSM-IV psychotic mood disorders with first-rank symptoms or bizarre delusions; ICD-10 'schizotypal disorder' which in DSM-IV is a personality disorder; the ICD-10 'acute and transient psychotic disorders' and the DSM-IV 'brief psychotic disorder'. Concerning diagnostic criteria, the reliability and validity of Schneiderian first-rank symptoms, 'bizarre' delusions and the Bleulerian 'negative' symptoms have been questioned. Validity studies in these areas are needed before it will be possible to provide major reconstructions for future diagnostic systems. One may hope that, eventually, one common worldwide psychiatric classification will be available.