In DSM-IV, the diagnosis of schizophrenia depends upon the presence of characteristic symptoms, a minimum duration of those symptoms, a minimum duration of the disorder, the presence of social/occupational dysfunction, and a differentiation from mood, schizoaffective, other psychotic disorders, general medical conditions, substance-induced disorders and pervasive developmental disorder. The DSM-IV diagnostic criteria of schizophrenia are shown in Table 1.2.

According to DSM-IV, there are no strictly pathognomonic symptoms of schizophrenia. Characteristic symptoms are conceptualized as falling into two broad categories: positive and negative. There are four groups of positive symptoms — delusions, hallucinations, disorganized speech, and grossly disorganized or catatonic behaviour—and one group of negative symptoms, which includes affective flattening, alogia and avolition.

Table 1.2. DSM-IV diagnostic criteria for schizophrenia

A. Characteristic Symptoms

Two (or more) of the following, each present for a significant portion of time during a 1-month period (or less if successfully treated);

(1) delusions

(2) hallucinations

(3) disorganized speech (e.g. frequent derailment or incoherence)

(4) grossly disorganized or catatonic behavior

(5) negative symptoms, that is, affective flattening, alogia, or avolition.

Note: Only one Criterion A symptom is required if delusions are bizarre or hallucinations consist of a voice keeping up a running commentary on the person's behavior or thoughts, or two or more voices conversing with each other.

B. 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 (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 6 months. This 6-month period must include at least 1 month of symptoms (or less if successfully treated) that meet Criterion A (i.e. active phase symptoms) and may include periods of prodromal or residual symptoms. During these prodromal or residual periods, the signs of the 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).

D. Schizoaffective and Mood Disorder exclusion

Schizoaffective Disorder and Mood Disorder With Psychotic Features have been ruled out because either (1) no Major Depressive, Manic or Mixed Episodes have occurred concurrently with the active-phase symptoms, or (2) if mood episodes have occurred during active-phase symptoms, their total duration has been brief relative to the duration of the active and residual periods.

E. Substance/general medical condition exclusion

The disturbance is not due to the direct physiological effects of a substance (e.g. a drug of abuse, a medication) or a general medical condition.

F. Relationship to a Pervasive Developmental Disorder

If there is a history of Autistic Disorder or another Pervasive Developmental Disorder, the additional diagnosis of Schizophrenia is made only if prominent delusions or hallucinations are also present for at least a month (or less if successfully treated).

The DSM-IV diagnostic criteria for schizophrenia require the presence of symptoms from at least two of the groups listed above. Symptoms from only one group are 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. Each of the symptoms must be present for a significant portion of time during a one-month period (or less if successfully treated).

According to DSM-IV, schizophrenia is accompanied by marked social or occupational dysfunction for a significant portion of the time since the onset of the disturbance. The dysfunction must be present in at least one major area such as work, interpersonal relations or self-care.

DSM-IV requires that continuous signs of the disturbance persist for at least 6 months. This 6-month period may include periods when only negative or less severe symptoms are present. Such periods are referred to as prodromal or residual, depending on whether they precede or follow the one-month period of characteristic symptoms described above.

Classification of course can be applied only after at least one year has elapsed since the initial onset of active-phase symptoms. According to DSM-IV, the course of schizophrenia is variable. The manual lists the following course specifiers: episodic with inter-episode residual symptoms; episodic with no inter-episode residual symptoms; continuous; single episode in partial remission; single episode in full remission; other or unspecified pattern.

Concerning differential diagnosis, DSM-IV emphasizes the distinction between schizophrenia and mood disorders. If psychotic symptoms occur exclusively during periods of mood disturbance, the diagnosis is mood disorder with psychotic features. If mood episodes have occurred during active-phase symptoms, and if their total duration has been brief relative to the duration of active and residual periods, the diagnosis is schizophrenia.

If a mood episode is concurrent with the active-phase symptoms of schizophrenia, and if mood symptoms have been present for a substantial portion of the total duration of the disturbance, and if delusions or hallucinations have been present for at least 2 weeks in the absence of prominent mood symptoms, the diagnosis is schizoaffective disorder.

The differentiation between schizophrenia, brief psychotic disorder and schizophreniform disorder rests upon a criterion of duration: less than one month for brief psychotic disorder; more than one month but less than 6 months for schizophreniform disorder; at least 6 months for schizophrenia.

The differential diagnosis between schizophrenia and delusional disorder rests on the nature of the delusions (in delusional disorder they are nonbizarre) and the absence of other characteristic symptoms of schizophrenia such as hallucinations, disorganized speech and behaviour, or prominent negative symptoms.

Schizophrenia and pervasive developmental disorder are distinguished by a number of criteria, including in particular the presence of prominent delusions and hallucinations in the former but not in the latter.

Finally, the diagnosis is not made if the disturbance is due to the direct physiological effects of a substance or a general medical condition.

DSM-IV describes five subtypes of schizophrenia: paranoid, disorganized, catatonic, undifferentiated and residual. Post-psychotic depressive disorder of schizophrenia and simple deteriorative disorder or simple schizophrenia are described in Appendix B, among conditions requiring further study.

In both the ICD-10 and the DSM-IV there is a distinction between positive and negative characteristic symptoms of schizophrenia. According to the definition provided in DSM-IV, ''the positive symptoms appear to reflect an excess or distortion of normal functions, whereas the negative symptoms appear to reflect a diminution or loss in normal functions''.

In both ICD-10 and DSM-IV, positive symptoms include hallucinations and delusions, disorganized thought and speech, as well as disorganized and catatonic behaviour. In both systems, negative symptoms include affective flattening or blunting of emotional responses, alogia or paucity of speech, and apathy or avolition.

The reliability and validity of psychiatric diagnoses that are based on explicit diagnostic criteria have been investigated in a number of studies during recent decades. According to Kendell [106], psychiatric diagnoses are now as reliable as the clinical judgements made in other branches of medicine. High reliability does not, however, by itself predict high validity. In fact, reliability can be high while validity remains trivial. In a critique of the DSM-IV operational diagnostic criteria for schizophrenia, Maj[l07] discusses several important issues. According to Maj, the symptomatological criterion does not characterize schizophrenia as a syndrome, the five groups of symptoms it mentions are all given the same weight, there is no clear indication concerning the threshold above which the clinical manifestations listed in the criterion should be regarded as symptoms, and the concept of bizarre delusions has been kept despite the empirical evidence of the poor reliability in the evaluation of a delusion as bizarre or non-bizarre. Most of these critiques can also be addressed to the ICD-10 criteria for schizophrenia. In addition to the preceding critiques, Majalso critically analyses the chronological criterion (6 months) used in DSM-IV, the definition of the functional criterion, and the aetiologic component implied in the exclusion criteria.

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