How is schizophrenia diagnosed? 

Diagnostic scales are widely used within clinical practice and research settings. These scales have been extensively validated and provide a set of criteria that is used to define and diagnose an illness. Two key examples include the American Psychiatric Association’s Diagnostic and Statistical Manual (DSM) and the World Health Organization’s International Classification of Diseases (ICD). Both the DSM and ICD criteria are regularly updated, and the most recent versions are the DSM-5 and the ICD-10. For a DSM-5 diagnosis of schizophrenia, at least two symptoms need to have been present for at least six months, and for a significant portion of time over a one-month period. Symptoms include delusions, hallucinations, disorganised speech and behaviour, catatonic behaviour, and negative symptoms such as diminished emotional expression, poverty of speech, and lack of purposeful action. At least one symptom of delusions, hallucinations, or disorganised speech needs to be present, and there also needs to be significant social or occupational dysfunction. For an ICD-10 diagnosis of schizophrenia, either at least one symptom of delusions, hallucinations, or thought symptoms (thought echo, insertion, withdrawal, or broadcasting) needs to be present, or at least two symptoms of hallucinations, negative symptoms, catatonic behaviour, or incoherent/irrelevant speech needs to be present for most of the time for at least one month.

What is the evidence on schizophrenia diagnosis?

Moderate to high quality evidence finds the DSM-III, DSM-III-R, and DSM-IV diagnostic criteria assigns more males with psychosis to a schizophrenia diagnosis (rather than any other psychosis diagnosis), while the ICD-9 shows no differences in gender distribution. Males are also found to have more negative symptoms.

Moderate quality evidence find Black people in the United States are more likely to be diagnosed with schizophrenia than White people in the United States. This effect was largest in studies with more males, more White patients, more young patients, studies in hospital or military settings, and studies conducted in the Midwest, Southeast, National, or multistate USA.

Moderate to high quality evidence suggests the proportion of first-episode psychosis patients retaining a diagnosis of schizophrenia over time is around 90%, and 72% for schizoaffective disorder. Also, the rate of a schizophrenia diagnosis following a diagnosis of schizophreniform disorder is around 65% over four years. Following brief, atypical, or not otherwise specified psychoses, the rate of a schizophrenia diagnosis is around 36% over four years. Following a substance-induced psychosis, the rate of a schizophrenia diagnosis is around 25% over four years. The rates of a transition to schizophrenia were highest for cannabis-induced psychosis, hallucinogen-induced psychosis, and amphetamine-induced psychosis.

Moderate to high quality evidence suggests better reliability for a diagnosis of schizophrenia than for a diagnosis of schizoaffective disorder. There was also evidence to support vector machines combined with other machine learning techniques applied to structural and functional neuroimaging data (particularly prefrontal and temporal) for assisting the clinical diagnosis of schizophrenia.

August 2020

Last updated at: 3:37 am, 28th August 2020
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