Schizotypal disorder in ICD-10 is classified in the ‘Schizophrenia and other psychotic disorders’ section as this disorder is described as possessing many of the characteristic features of schizophrenia without its obvious delusions and hallucinations.

The diagnosis requires the presence of more than three of the characteristic features without meeting the criteria for schizophrenia itself.  In contrast,  DSM-IV classifies the condition with the cluster A personality disorders, such as schizoid and paranoid.

Persistent delusional disorder of ICD-10 and delusional disorder of DSM-IV have similar diagnostic criteria except for differences in the duration of illness required, which is 3 months in ICD-10 and only 1 month in DSM-IV. Both classifications define this condition by the presence of a non-bizarre persistent delusion or set of related delusions. DSM-IV, in addition, specifies seven subtypes of this condition.

Any disorder of acute onset with typical schizophrenic features or other psychotic features lasting for more than 1 day to less than 1 month is classified in DSM-IV as brief psychotic disorder. This disorder is associated with a return to the premorbid level of functioning with good prognosis and may or may not be associated with marked stressors. This condition in ICD-10 is classed as acute and transient psychotic disorder. If the disorder persists for more than 1 month with schizophrenia-like symptoms, it is classified as schizophrenia in ICD-10, whereas in DSM-IV it will be classed as schizophreniform disorder. It will only be reclassified as schizophrenia if it lasts for more than 6 months.  If the acute and transient psychosis has features
of schizophrenia and has non-bizarre delusions, DSM-IV will class it as delusional disorder after 1 month whereas ICD-10 will class it as persistent delusional disorder only after a 3-month duration.

Schizoaffective disorder is diagnosed according to ICD-10 when both definite affective symptoms and schizophrenic symptoms are prominent simultaneously or within a few days of each other within the same episode of illness. In addition, DSM-IV requires the presence of typical schizophrenic features for at least 2 weeks along with the presence of prominent mood features.  A substantial proportion of the illness should be characterized by the presence of mood features. Both classifications subdivide the disorder into manic or bipolar type and depressive type.

Induced delusional disorder is a rare disorder defined in ICD 10 as a condition in which two or more people share the same delusion or delusional system, support each other in this belief and have an unusually close relationship. The dominant person usually develops the illness first and induces the delusion later in the passive person.  The DSM-IV diagnostic criteria for this illness are the same,  although the disorder is called shared psychotic disorder.

Both ICD-10 and DSM-IV, while providing the basis for an effective communication between the professionals and a basis for research,  also confer the disadvantages of creating an impression of discrete entities by imposing a framework on what are in fact complex and overlapping phenomena. These classification systems are complex, difficult to follow in dayto-day practice and the criteria are constantly revised; consequently, the research based on these systems becomes rapidly obsolete and difficult to apply in a clinical setting. Nevertheless, it is very hard to imagine working in a complex field such as schizophrenia and related psychotic disorders and not having a reasonable level of shared understanding of modern widely used concepts and definitions.