ICD-10 and DSM-IV concepts of schizophrenia and related disorders

Although attempts have been made to bridge the gap between ICD-10 and DSM-IV and move them closer, significant differences still persist concerning the definition, duration and subtypes of schizophrenia and the nomenclature of various other psychotic disorders classified with schizophrenia. ICD-10 classifies schizotypal disorder, persistent delusional disorder, acute and transient psychotic disorders, induced delusional disorder and schizoaffective disorders together with schizophrenia (Table 1.1). DSM-IV does not include the category of schizotypal disorders with psychotic disorders but classifies it along with cluster A personality disorders.

Induced delusional disorder in ICD-10 is called shared psychotic disorder in DSM-IV; persistent delusional disorder in ICD-10 is called delusional disorder in DSM-IV (Table 1.2). The major difference is in the category of acute and transient psychotic disorder of ICD-10, which overlaps with brief psychotic disorder and schizophreniform disorder of DSM-IV.

The other major difference is in the classification of psychotic illness secondary to substance misuse and to general medical conditions, which are classified together with schizophrenia in DSM-IV but are classified with disorder due to psychoactive substance misuse (F10–F19) and organic mental disorder (F00–F09), respectively, in ICD-10.

Table 1.1 Brief outline of ICD-10 classification of schizophrenia and other psychotic disorders.

F20 Schizophrenia
F21 Schizotypal disorder
F22 Persistent delusional disorder
F23 Acute and transient psychotic disorders
F24 Induced delusional disorders
F25 Schizoaffective disorder
F28 Other non-organic psychotic disorders
F29 Unspecified non-organic psychosis

ICD-10 avoids criteria based on social and occupational dysfunction for the diagnosis of schizophrenia on the basis that it is difficult to equate these criteria between different cultures.

This is a major inclusion criterion in DSM-IV that is essential for the diagnosis of schizophrenia.

Diagnostic criteria for schizophrenia

ICD-10 requires either one of the Schneiderian first-rank symptoms, or bizarre delusions, or two or more symptoms including persistent hallucinations, thought disorder, catatonic behaviour, negative symptoms or significant and persistent behavioural change. These features are required to be present for a 1-month duration or longer. ICD-10 recognizes that there may be a prodromal phase associated with schizophrenia, but as a prodrome typical of and specific to schizophrenia could not be described reliably it is not included in the diagnostic criteria. The 1-month duration of schizophrenia according to ICD-10 does not include the prodromal phase ().