The diagnosis of schizophrenia, a psychotic disorder, is based on criteria in either the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, or the World Health Organization's International Classification of Diseases (ICD). Clinical assessment of schizophrenia is carried out by a mental health professional based on observed behavior, reported experiences, and reports of others familiar with the person. Diagnosis is usually made by a psychiatrist. Associated symptoms occur along a continuum in the population and must reach a certain severity and level of impairment before a diagnosis is made. Schizophrenia has a prevalence rate of 0.3-0.7% in the United States
Criteria
In 2013, the American Psychiatric Association released the fifth edition of the DSM (DSM-5). According to the manual, to be diagnosed with schizophrenia, two diagnostic criteria have to be met over much of the time of a period of at least one month, with a significant impact on social or occupational functioning for at least six months. The DSM diagnostic criteria outlines that the person has to be experiencing either delusions, hallucinations, or disorganized speech. In other words, an individual does not have to be experiencing delusions or hallucinations to receive a diagnosis of schizophrenia. A second symptom could be negative symptoms, or severely disorganized or catatonic behavior. Only two symptoms are required for a diagnosis of schizophrenia, resulting in different presentations for the same disorder.
In practice, agreement between the two systems is high. The DSM-5 criteria puts more emphasis on social or occupational dysfunction than the ICD-10. The ICD-10, on the other hand, puts more emphasis on first-rank symptoms. The current proposal for the ICD-11 criteria for schizophrenia recommends adding self-disorder as a symptom.
Changes made
Both manuals have adopted the chapter heading of Schizophrenia spectrum and other psychotic disorders; ICD modifying this as Schizophrenia spectrum and other primary psychotic disorders. The definition of schizophrenia remains essentially the same as that specified by the 2000 text revised DSM-IV (DSM-IV-TR). However, with the publication of DSM-5, the APA removed all sub-classifications of schizophrenia. ICD-11 has also removed subtypes. The removed subtype from both, of catatonic has been relisted in ICD-11 as a psychomotor disturbance that may be present in schizophrenia.
Another major change was to remove the importance previously given to Schneider's first-rank symptoms. DSM-5 still uses the listing of schizophreniform disorder but ICD-11 no longer includes it. DSM-5 also recommends that a better distinction be made between a current condition of schizophrenia and its historical progress, to achieve a clearer overall characterization.
A dimensional assessment has been included in DSM-5 covering eight dimensions of symptoms to be rated (using the Scale to Assess the Severity of Symptom Dimensions) – these include the five diagnostic criteria plus cognitive impairments, mania, and depression. This can add relevant information for the individual in regard to treatment, prognosis, and functional outcome; it also enables the response to treatment to be more accurately described.
Two of the negative symptoms – avolition and diminished emotional expression – have been given more prominence in both manuals.
First rank symptoms
First-rank symptoms are psychotic symptoms that are particularly characteristic of schizophrenia, which were put forward by Kurt Schneider in 1959. Their reliability for the diagnosis of schizophrenia has been questioned since then. A 2015 systematic review investigated the diagnostic accuracy of first rank symptoms:
Heterogeneity
Sub-classifications
The DSM-IV-TR contained five sub-classifications of schizophrenia. The sub-classifications were removed in the DSM-5 due to the conditions' heterogeneous nature and their historical insignificance in clinical practice. These were retained in previous revisions largely for reasons of tradition, but had subsequently proved to be of little worth.
The ICD-10 defines seven sub-classifications of schizophrenia. These sub-classifications are:
Country-specific versions
The ICD-10 Clinical Modification, used for medical coding and reporting in the United States excludes the post-schizophrenic depression (F20.4) and the Simple (F20.6) sub-classifications.
The Russian version of the ICD-10 includes additional four sub-classifications of schizophrenia: hypochondriacal (F20.801), cenesthopathic (F20.802), childhood type (F20.803), and atypical (F20.804).