Classification of nonschizophrenic psychotic disorders: a historical perspective.

The existence of a group of psychoses that are symptomatologically and prognostically different from schizophrenia and affective psychotic disorders is supported by clinical and epidemiologic evidence. Although such "atypical" psychoses account for up to 10% of all psychotic disorders, their aetiology, pathophysiology, and neuropathology remain insufficiently understood. Moreover, they have been described by different schools of psychiatry a variety of ways, including non-process schizophrenia, schizophreniform psychosis, reactive (or psychogenic) psychosis, bouffées délirantes, and cycloid psychoses, but the extent to which these diagnostic categories overlap or differ has not been systematically explored. Neither Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), nor International Classification of Disease, Tenth Revision (ICD-10), provides adequate diagnostic criteria and classificatory categories for this group of disorders. Special attention to the refinement of the diagnosis and classification of the acute and transient psychotic disorders in future versions of the two classifications will be warranted.