In order for a person to be diagnosed with schizophrenia, certain diagnostic criteria for schizophrenia must be met. In the United States, the Diagnostic and Statistical Manual of Mental Health Disorders (DSM-IV-TR) is used by mental health professionals to help decide whether a person is suffering from schizophrenia; in Europe, the ICD-10 criteria are used.
According to the DSM-IV-TR, the symptoms of schizophrenia (which must have been present for between one and six months) can be defined as positive and negative: positive symptoms include hallucinations and delusional behaviour, whereas negative symptoms include a loss of motivation and flat emotions.
What are the diagnostic criteria for schizophrenia?
The DSM criteria for schizophrenia are a list of symptoms that must be present in order for a patient to be diagnosed with schizophrenia. These include the following:
A. Two or more of these characteristic symptoms should be present for much of the time over the course of a one month period:
- Catatonic or grossly disorganised behaviour
- Disorganised speech featuring incoherence
- Negative symptoms such as a noticeable decline in emotional response, a decline in speech, or a decline in motivation
B. Social or occupational dysfunction that affects work, personal relationships, or self care is noticeable and has been present since the onset of symptoms
C. Disturbances of behaviour should have been present for at least six months and symptoms must be present for at least one month of that six month period.
D. Some of the symptoms of schizophrenia are also seen in other mood disorders, so for schizophrenia to be diagnosed, these other conditions must be excluded. Psychotic episodes can be seen in patients suffering from bipolar disorder, but the DSM criteria for schizophrenia says that schizoaffective disorder and mood disorders such as bipolar can be ruled out if the patient has not had a major depressive or manic episode (or mixed episode) at the same time as any positive schizophrenia symptoms.
Substance abuse must be excluded in order for a diagnosis of schizophrenia to be made.
E. When the patient has a history of another developmental disorder or autism, the DSM-IV-TR states that schizophrenia can only be diagnosed if major episodes of hallucinations or delusions have been present for at least one month.
Sub-types of schizophrenia
The DSM-IV-TR also lists the diagnostic criteria for schizophrenia sub-types. These are normally defined by the dominant symptoms at the time of evaluation and diagnosis and include:
Paranoid type: delusions and hallucinations are the prominent symptoms
Catatonic type: at least two symptoms must be present, including excessive motor activity, stupor, extreme negativism or mutism, peculiarities of voluntary movement, and echopraxia or echolalia
Disorganized type: disorganised speech, flat emotions, or disorganised behaviour are the prominent symptoms
Residual type: behaviour is disturbed, but there are no prominent hallucinations, delusions, catatonia or disturbed behaviour
Undifferentiated type: the patient meets criteria A for schizophrenia, but does not fall into the sub-types of paranoid, catatonic, or disorganised schizophrenia.
Schizoaffective disorder will be diagnosed if the patient meets the criteria of A, D and E, but has shown symptoms at least one month, but less than six months.