2. ICD‐10 criteria for schizophrenia.

Although no strictly pathognomonic symptoms can be identified, for practical purposes it is useful to divide symptoms into groups that have special importance for the diagnosis and often occur together, such as:

a) thought echo, thought insertion or withdrawal, and thought broadcasting;

b) delusions of control, influence, or passivity, clearly referred to body or limb movements or specific thoughts, actions, or sensations; delusional perception;

c) hallucinatory voices giving a running commentary on the patient's behaviour, or discussing the patient among themselves, or other types of hallucinatory voices coming from some part of the body;

d) persistent delusions of other kinds that are culturally inappropriate and completely impossible, such as religious or political identity, or superhuman powers and abilities (e.g. being able to control the weather, or being in communication with aliens from another world);

e) persistent hallucinations in any modality, when accompanied either by fleeting or half‐formed delusions without clear affective content, or by persistent over‐valued ideas, or when occurring every day for weeks or months on end;

f) breaks or interpolations in the train of thought, resulting in incoherence or irrelevant speech, or neologisms;

g) catatonic behaviour, such as excitement, posturing, or waxy flexibility, negativism, mutism, and stupor;

h) "negative" symptoms such as marked apathy, paucity of speech, and blunting or incongruity of emotional responses, usually resulting in social withdrawal and lowering of social performance; it must be clear that these are not due to depression or to neuroleptic medication;

i) a significant and consistent change in the overall quality of some aspects of personal behaviour, manifest as loss of interest, aimlessness, idleness, a self‐absorbed attitude, and social withdrawal.

The normal requirement for a diagnosis of schizophrenia is that a minimum of one very clear symptom (and usually two or more if less clear‐cut) belonging to any one of the groups listed as (a) to (d) above, or symptoms from at least two of the groups referred to as (e) to (h), should have been clearly present for most of the time during a period of 1 month or more. Conditions meeting such symptomatic requirements but of duration less than 1 month (whether treated or not) should be diagnosed in the first instance as acute schizophrenia‐like psychotic disorder and are classified as schizophrenia if the symptoms persist for longer periods.

ICD: International Statistical Classification of Diseases