Like many mental illnesses, the diagnosis of schizophrenia is based upon the
behaviour of the person being assessed. There is a list of diagnostic criteria
which must be met for a person to be so diagnosed. These depend on both the
presence and duration of certain signs and symptoms.
The most commonly-used criteria for diagnosing schizophrenia are from the American
Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders
(DSM) and the World Health Organisation's International Statistical Classification
of Diseases and Related Health Problems (ICD). The most recent versions are
ICD-10 (http://www.who.int/whosis/icd10/) and DSM-IV-TR (http://www.psych.org/research/dor/dsm/index.cfm).
Below is an abbreviated version of the diagnostic criteria from the DSM-IV-TR,
the full version is available here (http://www.behavenet.com/capsules/disorders/schiz.htm).
To be diagnosed as having schizophrenia, a person must display:
Characteristic 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)
delusions
hallucinations
disorganized speech (e.g., frequent derailment or incoherence). See
thought disorder.
grossly disorganized or catatonic behavior
negative symptoms, i.e., affective flattening (lack or decline in emotional
response), alogia (lack or decline in speech), or avolition (lack or decline
in motivation).
Note: Only one Criterion A symptom is required if delusions are bizarre
or hallucinations consist of hearing voices.
Social/occupational dysfunction: For a significant portion of the time since
the onset of the disturbance, one or more major areas of functioning such
as work, interpersonal relations, or self-care, are markedly below the level
achieved prior to the onset.
Duration: Continuous signs of the disturbance persist for at least six months.
This six-month period must include at least one month of symptoms (or less,
if successfully treated) that meet Criterion A.
Historically, schizophrenia in the West was classified into simple, catatonic,
hebephrenic, and paranoid. The DSM now contains five sub-classifications of
schizophrenia. These are
catatonic type (where marked absences or peculiarities of movement are present),
disorganised type (where thought disorder and flat or inappropriate affect
are present together),
paranoid type (where delusions and hallucinations are present but thought
disorder, disorganised behaviour, and affective flattening is absent),
residual type (where positive symptoms are present at a low intensity only)
and
undifferentiated type (psychotic symptoms are present but the criteria for
paranoid, disorganized, or catatonic types has not been met).
Symptoms may also be described as 'positive symptoms' (those additional to normal
experience and behaviour) and negative symptoms (the lack or decline in normal
experience or behaviour). 'Positive symptoms' describe psychosis and typically
include delusions, hallucinations and thought disorder. 'Negative symptoms'
describe inappropriate or nonpresent emotion, poverty of speech, and lack of
motivation.
It is worth noting that many of the positive or psychotic symptoms may occur
in a variety of disorders and not only in schizophrenia. The psychiatrist Kurt
Schneider tried to list the particular forms of psychotic symptoms which he
thought were particularly useful in distinguishing between schizophrenia and
other disorders which could produce psychosis. These are called first rank symptoms
or Schneiderian first rank symptoms and include delusions of being controlled
by an external force, the belief that thoughts are being inserted or withdrawn
from your conscious mind, the belief that your thoughts are being broadcast
to other people and hearing hallucinated voices which comment on your thoughts
or actions, or may have a conversation with other hallucinated voices. It now
seems that 'first rank symptoms' are not a reliable method of diagnosing schizophrenia4,
however the term might still be used descriptively by mental health professionals.
Schizophrenia: Diagnostic issues and controversies
