First-episode psychosis: diagnostic stability over one and two years.

BACKGROUND: Diagnostic stability is important for daily clinical work and planning of treatment. The aims of this study were to measure diagnostic stability in a clinical epidemiologic sample and to identify markers of change in diagnosis.

SAMPLING AND METHODS: Diagnostic stability and change were measured in a sample of 301 patients with first-episode psychosis from four national health care sectors in Norway and Denmark at baseline, 1 and 2 years.

RESULTS: Diagnostic stabilities were high for schizophrenia and schizoaffective disorder (85-99%), low for schizophreniform disorder (16-19%), and intermediate for other diagnoses. Diagnostic change from schizophreniform to schizophrenia was frequent in year 1 (72%). Characteristics discriminating schizophreniform patients keeping their diagnosis (i.e. having recovered within 6 months with no relapse) from those developing schizophrenia at 1 year were female gender, better childhood premorbid functioning, shorter duration of untreated psychosis and more severe general psychotic symptoms, especially excitation.

CONCLUSIONS: Findings provide validation for the DSM-IV categories within the schizophrenic spectrum. The limitations of the study were: the raters were not blind to baseline assessments; patients with longer duration of untreated psychosis were more likely to refuse participation; not all patients were assessed at 1- and 2-year follow-up, but the attrition was rather low.