Diagnosing schizophrenia is difficult because there is no single symptom which is unique to schizophrenia and there are no definitive blood tests or scans for the disorder. Making a diagnosis currently requires recognising a constellation of symptoms for at least 6 months. Seeing a deterioration in the level of functioning of the person with the symptoms, as well as 'ruling out' other possible explanations for the observed disturbance.
There are two major systems currently used for the diagnosis of schizophrenia, the Diagnostic and Statistical Manual of Mental Disorders and the International Classification of Disease. These classifications have improved the reliability of diagnosis.
Diagnostic & Statistical Manual of Mental Disorders (DSM-V) Criteria for Schizophrenia:
A. Characteristics of Symptoms: TWO OR MORE of the following, each present for a significant portion of time during a one month period (or less if successfully treated):
- Disorganised speech (e.g. frequent derailment or incoherence)
- Grossly disorganised or catatonic behaviour
- Negative symptoms, ie affective flattening, alogia or avolition
(Note: Only one "A" symptom is required if delusions are bizarre or hallucinations consist of a voice keeping up a running commentary on the person's behaviour or thoughts, or two or more voices conversing with each other).
B. Social/Occupational Dysfunction: for a significant portion of time since the onset of the disturbance, one or more major areas of functioning, such as work, interpersonal relations or self-care is markedly below the level achieved prior to the onset (or when the onset is in childhood or adolescence, failure to achieve expected level of interpersonal, academic or occupational achievement).
C. Duration: continuous signs of the disturbance persist for at least six months. This six month period must include at least one month of symptoms that meet criterion A (ie active phase symptoms) and may include periods of prodromal or residual symptoms. During these prodromal or residual periods, the signs of disturbance may be manifested by only negative symptoms or two or more symptoms listed in criterion A present in an attenuated form, e.g. odd beliefs, unusual perceptual experiences).
Exclusion Criteria: the remainder of the criteria (D-F in the DSM-IV text) specify that the signs and symptoms above are not better accounted for by another disorder, either psychiatric (ie mood disorder, schizoaffective disorder or pervasive developmental disorder), substance abuse (e.g. amphetamine intoxication or withdrawal) or a general medical condition (e.g. hyperthyroidism).
International Classification of Disease (ICD-10) Criteria for Schizophrenia:
Either at least one of the syndromes, symptoms and signs listed below under (1) or at least two of the symptoms and signs listed under (2) would have been present for most of the time during an episode of psychotic illness lasting for at least 1 month.
1. At least ONE of the following:
- Thought echo, thought insertion or withdrawal and thought broadcasting.
- Delusions of control, influence or passivity, clearly referred to body or limb movements or specific thoughts, actions or sensations, and delusional perception.
- Hallucinatory voices giving a running commentary on the patient's behaviour or discussing him/her between themselves or other types of hallucinatory voices coming from some part of the body.
- Persistent delusions of other kinds that are culturally inappropriate or implausible, such as religious or political identity, superhuman powers and ability etc.
2. At least TWO of the following:
- Persistent hallucinations in any modality, when accompanied by either 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.
- Breaks of interpolations in the train of thought, resulting in incoherence or irrelevant speech or neologisms.
- Catatonic behaviour, such as excitement, posturing or waxy flexibility, negativism, mutism and stupor.
- Negative symptoms such as marked apathy, paucity of speech and blunting or incongruity of emotional responses (these usually result in social withdrawal and lowering of social performance). It must be clear that these are not due to depression or neuroleptic medication.
- 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.
Exclusion Criteria: The ICD-10 criteria specify that schizophrenia should not be diagnosed if the symptoms are better accounted for by a mood disorder, 'overt brain disease' or drug intoxication or withdrawal.