Diagnosis, Classification, and Differential Diagnosis of Schizophrenia

Anthony S. David

The diagnosis of schizophrenia

Until the early 1970s, the diagnosis of schizophrenia was one of the most contentious and fraught issues in the whole of psychiatry. Since then a massive international effort has been put in motion out of which explicit diagnostic criteria emerged. Some achieved widespread and even multinational agreement, allowing the painstaking process of calculating diagnostic specificity, sensitivity, reliability, and (perhaps) validity to begin. Although criticism of the diagnosis of schizophrenia continues, mostly from outside psychiatrists, the vast majority of psychiatrists look upon the major sets of diagnostic criteria with weary acceptance, seeing them as flawed but useful and possibly ‘as good as it gets’ given our current state of knowledge/ignorance.

Throughout the 1970s and early 1980s there was an overabundance of criteria including the St. Louis criteria⁽¹⁾ and the Research Diagnostic Criteria,⁽²⁾ followed by the Present State Examination (PSE-CATEGO), the ICD-9, and the DSM-III. Perhaps because of the ‘cookbook’ explicitness of the DSM-III or the pervasive influence of American psychiatric practice, dubbed by some ‘neocolonial’, the DSM, in its fourth revision with a fifth due in 2010, is the mostly widely used. The ICD-10 is also used throughout the world, but seldom in North America.

Diagnostic criteria

The signs and symptoms of schizophrenia and related disorders are discussed in detail in Chapter 4.3.2. Also, the diagnostic process is described in general in Chapter 1.8.1. As noted, the signs and symptoms, weighted in terms of their typicality or specificity, combined with additional clinical factors such as onset, duration, social consequences, etc., are used to make a diagnosis of schizophrenia and subsequently to classify the disorder into subtypes. The DSM and ICD criteria are described below (Tables 4.3.4.1, 4.3.4.2 and 4.3.4.3).

Table 4.3.4.1 Major diagnostic criteria for schizophrenia

		DSM-IV	ICD-10
Characteristic symptoms
	One or more for 1 month	1. Bizarre delusions	1. Thought echo/insertion/withdrawal/broadcasting
		2. Commenting voice or voices conversing	2. Delusions of control
			3. Hallucinatory voices
			4. Persistent delusions
	Or two or more	1. Delusions	1. Persistent hallucinations
		2. Hallucinations	2. Thought block/disorder
		3. Disorganized speech	3. Catatonia
		4. Grossly disorganized or catatonic behaviour	4. Negative symptoms
		5. Negative symptoms	5. Significant personality change
Time course		1 month (‘significant proportion’) for symptoms listed plus 6 months social/occupational disturbance	1 month (most of the time)
Exclusions		Schizoaffective disorder or brief mood disturbance Direct effect of drugs of abuse/ medication or general medical condition	Extensive depressive/manic symptoms or diagnosis of schizoaffective disorder Overt brain disease; drug intoxication/withdrawal

Another group of psychotic disorders which may be distinguished on the basis of formal phenomenological properties are the delusional disorders⁽³^, ⁴⁾ formally known as paranoia (see Chapter 4.4).

Basis of classification

Atheoretical: Schneider’s first-rank symptoms

These are still important for the diagnosis of schizophrenia using the ICD-10 frame of reference. They are too rare to achieve high levels of sensitivity and their specificity has been challenged. Nevertheless, first-rank symptoms perform creditably on these parameters when compared to negative symptoms.⁽⁵^,⁶⁾ On the other hand, the lack of aetiological and prognostic significance of first-rank symptoms has undermined the prominence claimed for them.⁽⁷^,⁸⁾ The negative⁽⁹⁾ or so-called deficit syndrome⁽¹⁰⁾ relates more consistently to outcome/prognosis and shows more stability over time. The constituent symptoms such as social withdrawal, apathy, lack of initiative, and self-care, have rather poor diagnostic specificity in isolation and must be distinguished from depression and parkinsonism, chronic drug dependence, and organic brain damage.

Table 4.3.4.2 Criteria for the diagnosis of schizophrenia subtypes

Schizophrenia subtypes	DSM-IV	ICD-10
Paranoid	One or more delusions plus frequent auditory hallucinations; no prominent thought disorder, catatonia, or negative symptoms	Delusions, hallucinatory voices, hallucinations in other modalities; disturbances of affect, volition, and speech ‘inconspicuous’
Disorganized DSM Hebephrenic ICD	Prominent disorganized speech behaviour and flat/inappropriate affect; no catatonia	Prominent disturbances of affect, volition, and thought; 2–3 months duration; adolescents/young adults only
Catatonic	Two of motoric immobility, excessive activity, negativism, peculiar voluntary movements, echolalia/ praxia	One or more of stupor, excitement. posturing, negativism, rigidity, waxy flexibility, automatic compliance and perserveration
Undifferentiated	Meets criteria for schizophrenia but none of the above subtypes	Meets criteria for schizophrenia but none of the above subtypes plus residual
Residual	Absence of prominent characteristic symptoms (but two or more must be present in attenuated form); continuing evidence of disturbance including negative symptoms	Prominent negative symptoms; clear-cut episode(s) in past; at least 1 year history; no dementia or depression etc.
Simple	Slowly progressive negative symptoms without other psychotic symptoms	(See schizoid personality disorder)

Theoretical

Attempts at a theoretical classification have been made. The first in the modern era was Crow’s Type I and Type II distinction,⁽¹¹⁾ although it echoes older notions of ‘process’-chronic and deteriorating versus ‘reactive’ (relapsing and remitting) typologies. The innovation was to link the distinction with proposed differences in dopamine receptor hyperactivity (Type I), associated with positive symptoms and good response to dopamine antagonist drugs, and on the other hand, to neurological damage (Type II) as evidenced by ventricular enlargement on Computerized Tomography (CT) brain scans, associated with chronicity, poor premorbid functioning, and poor response to treatment.

Table 4.3.4.3 Terminology used to describe the course of schizophrenia in the DSM-IV and ICD-10 classifications

DSM-IV	ICD-10
Continuous	Continuous
Episodic with residual symptoms	Episodic with stable deficit
Episodic with no interepisode symptoms	Episodic remittent
Single episode in partial remission	Incomplete remission
Single episode in full remission	Complete remission
Other	Other
	Episodic with progressive deficit
^aCourse specifiers in both DSM-IV and ICD-10 require 1 year of observation.

Building on this was the ‘aetiological classification’ proposed by Murray et al.⁽¹²⁾ which contrasted cases with a presumed genetic aetiology and those who had other putative risk factors such as early brain damage (see Chapter 4.3.6.1). Although these attempts have served as useful stimuli for research, they have not been found to aid clinical decision-making and in fact now appear to support a blurring of diagnostic boundaries rather than a sharpening or subdivision.⁽¹³⁾ In fact the search for ‘biological markers’ often called ‘endophenotypes’, which might validate diagnostic distinctions continues. Take for example, the presence of ventricular enlargement or cortical thinning, first detected using CT and now magnetic resonance imaging (MRI). Meta-analyses have confirmed that indices of ‘cerebral atrophy’ are strongly associated with schizophrenia but the effect sizes are small.⁽¹⁴⁾ Medial temporal lobe structures are the region of most grey matter volume loss. However, there is substantial overlap between normal controls and schizophrenia cases and MRI cannot be considered a useful diagnostic test. A host of genetic markers have been identified in the last 5 years, each of small effect and some showing overlap between the major schizophrenic and affective syndromes.⁽¹⁵⁾

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