Diagnostic criteria

The current diagnostic criteria are purely clinical and not fully satisfactory. Controversies about the diagnosis of schizophrenia include the following:

• whether the term should be reserved for illnesses that result in permanent residual defects (nuclear or process schizophrenia) or may also be applied to acute episodes (schizophreniform reactions) that may resolve completely

• whether the different clinical types of 'schizophrenia' are variants of the same disease process or are separate conditions

• whether cases without positive symptoms should be included

• whether there is a valid distinction between schizophrenia and the affective psychoses.

When Krapelin described the condition in 1896 under the term dementia praecox, he distinguished it from manic-depressive illness because of its worse prognosis. E. Bleuler, who coined the term 'schizophrenia' in 1911, considered that the essential features were loosening of associations in thought, flattening or incongruity of affect, ambivalence and autism (withdrawal from reality), and some permanent defect in personality.

As Bleuler's symptoms cannot be precisely defined, widely differing concepts of 'schizophrenia' developed in different centres; for example, schizophrenia was diagnosed more readily in the USA, which followed the looser Bleulerian approach, than in the UK, which adopted the tighter Krapelinian view. The differences persisted until the later editions of the DSM, which came closer to the ICD view (see below).

In recent years, there have been attempts to standardize the definition. A popular criterion in Britain is that of Schneider's first rank symptoms. Schneider (1959) postulated the following set of symptoms, any one of which would be diagnostic of schizophrenia in a patient without organic brain disease:

• Two or more hallucinatory voices discuss the patient in the third person.

• Voices make a running commentary on his thoughts or actions.

• Voices repeat his thoughts aloud (écho de la pensée).

• There is thought insertion, or withdrawal.

• There is thought broadcasting.

• Bodily (somatic) feelings of influence: the patient has bodily symptoms which he feels are produced by some outside agency.

• Passivity feelings: the patient experiences his thoughts or actions as being controlled by some external agency.

• Delusional perception: a normal perception gives rise to a fully formed delusion; e.g. 'the red car has just gone past, so I am the Messiah.'

However, research has shown that Schneider's symptoms may occur in affective psychoses also; they do not necessarily predict long-term outcome. Nevertheless, they remain a useful diagnostic pointer.

The main systems in use today are the DSM-IV and the ICD-10. The current editions are now fairly similar (although widely different in the past). The main differences are in the duration required - in the ICD, 1 month; in the DSM, 6 months - and in social or occupational dysfunction, which is required in the DSM but not specified under ICD.

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