To examine the temporal stability of the category 'acute and transient psychotic disorders' (ATPDs), ICD-10 Classification of Mental and Behavioural Disorders, including subtypes characterised by polymorphic, schizophrenic and predominantly delusional features.
We checked the readmission patterns of all patients aged 15-64 years (n = 5426), whether admitted to hospital or treated as outpatients, who were enrolled for the first time in the Danish Psychiatric Register with a diagnosis of ATPDs between 1995 and 2008.
An increasing number of cases with ATPDs changed diagnosis in subsequent admissions after 1, 2 and 5 years, mainly either to schizophrenia and related disorders or affective disorders. In their last admission, on average after 7.3 years, there were 2429 patients listed with ATPDs, accounting for an overall stability of 44.8%. Females were less likely than males to develop another diagnosis. Among the ATPD subtypes, polymorphic psychotic disorder without schizophrenic symptoms had a higher stability than those featuring schizophrenic or predominantly delusional features.
The low diagnostic stability of ATPDs reflects the lack of clearly defining features and argues against their validity as a distinct category.