Background: Diagnostic stability is one measure of predictive validity for psychiatric syndromes. It is an under-studied area in functional psychosis despite its clinical and research implications. We aimed at evaluating the stability of ICD-10 diagnoses in a sample of young people with first-episode psychosis.
Method: One hundred and sixty-six Hong Kong Chinese enrolled in a regional first-episode psychosis treatment program were studied. Subjects' baseline and final 5-year consensus diagnoses were established via systematic medical records' review to determine diagnostic stability and to identify predictors of diagnostic shift towards schizophrenia spectrum.
Results: The overall diagnostic consistency was 80.7%. Bipolar affective disorder and schizophrenia were the most stable diagnostic categories over 5 years with prospective consistency of 100% and 95.8% respectively. The least stable baseline diagnoses were unspecified non-organic psychosis, acute and transient psychotic disorders and delusional disorder. Around one-fifth (19.3%) of subjects had diagnostic revision in 5 years. The predominant pattern of diagnostic shift was towards schizophrenia spectrum disorder. Family history of psychosis and longer duration of untreated psychosis were associated with diagnostic transition towards schizophrenia spectrum.
Conclusions: Schizophrenia and bipolar affective disorder were diagnostically stable and could be reliably classified at intake in a Chinese first-episode psychosis sample using the ICD-10 criteria. Diagnostic instability in the least prevalent categories of functional psychosis highlights the limitations of current taxonomies and calls for ongoing revision of diagnostic criteria. In the absence of biological marker, longitudinal validation across consecutive episodes is necessary for accurate diagnostic ascertainment.