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Chapter 1
Classification of Psychiatric Disorders
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Any discussion of the classification of psychiatric disorders should begin with the frank
admission that any definitive classification of disease must be based on its aetiology. Until
we know the causes of the various mental illnesses, we must adopt a pragmatic approach to
classification that will best enable us to care for our patients, to communicate with other
health professionals and to carry out high-quality research.
In physical medicine, syndromes existed long before the aetiology of these illnesses
was known. Some of these syndromes have subsequently been shown to be true disease
entities because they have one essential cause. Thus, smallpox and measles were carefully
described and differentiated by the Arabian physician Rhazes in the tenth century AD. With
each new step in the progress of medicine, such as auscultation, microscopy, immunology,
electrophysiology, etc., some syndromes have been found to be true disease entities, while
others have been split into discrete entities, and others still jettisoned. For example, diabetes
mellitus has been shown to be a syndrome that can have several different aetiologies. On
that basis, the modern approach to classification has been to establish syndromes in order to
facilitate research and to assist us in extending our knowledge of them so that, ultimately,
specific diseases can be identified. We must not forget that syndromes may or may not be
true disease entities, and some will argue that the multifactorial aetiology of psychiatric
disorder, related to both constitutional and environmental vulnerability, as well as to
precipitants, may make the goal of identifying psychiatric syndromes as discrete diseases an
elusive ideal.
Syndromes and Diseases
A syndrome is a constellation of symptoms that are unique as a group. It may of course
contain some symptoms that occur in other syndromes also, but it is the particular
combination of symptoms that makes the syndrome specific. In psychiatry, as in other
branches of medicine, many syndromes began with one specific and striking symptom. In
the nineteenth century, stupor, furore and hallucinosis were syndromes based on one
prominent symptom. 10
Later, the recognition that certain other signs and symptoms co-occurred
simultaneously led to the establishment of syndromes. Korsakoff’ s syndrome illustrates the
progression from symptom to syndrome to disease. Initially, confabulation and
impressionability among alcoholics were recognised by Korsakoff as significant symptoms.
Later, the presence of disorientation for time and place, euphoria, difficulty in registration,
confabulation and ‘ tram-line’ thinking were identified as key features of this syndrome.
Finally, the discovery that in the alcoholic amnestic syndrome there was always severe
damage to the mammillary bodies confirmed that Korsakoff’ s psychosis (syndrome) is a
true disease with a neuropathological basis .
Sometimes the symptoms of the syndrome seem to have a meaningful coherence. For
example, in mania the cheerfulness, the overactivity, the pressure of speech and the flight of
ideas can all be understood as arising from the elevated mood. The fact that we can
empathise with and understand our patients’ symptoms by taking account of the context in
which they have arisen has led to the distinction between those symptoms that are primary,
i.e., are the immediate result of the disease process, and secondary symptoms, which are a
psychological elaboration of, or reaction to, primary symptoms. The term ‘ primary’ is also
used to describe symptoms that cannot be derived from any other psychological event .
Early Distinctions
The first major classification of mental illness was based on the distinction between
disorders arising from disease of the brain and those with no such obvious basis, i.e.,
functional versus organic states. These terms are still used, but as knowledge of the
neurobiological processes associated with psychiatric disorders has increased and led to
greater nuance, their original meaning has been lost. Schizophrenia and manic depression
are typical examples of functional disorders, but the increasing evidence of the role of
genetics and of neuropathological abnormalities shows that there is at least some organic
basis for these disorders. Indeed, the category of ‘ organic mental syndromes and disorders’
was renamed as ‘ delirium, dementia and amnestic and other cognitive disorders’ in the
Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric
Association, 1994 ), so that the recognition of the role of abnormal brain functioning is not
confined to dementia and delirium only. In their literal meaning, these categories of
classification (i.e., organic versus functional) are absurd, yet they continue to be used
through tradition.
Organic Syndromes
The syndromes due to brain disorders can be classified into acute, subacute and chronic. In
acute organic syndromes the most common feature is alteration of consciousness, which can
be dream-like, depressed or restricted. This gives rise to four subtypes, namely, delirium,
subacute delirium, organic stupor or torpor and the twilight state. Disorientation,
incoherence of psychic life and some degree of anterograde amnesia are features of all of
these acute organic states. In delirium there is a dream-like change in consciousness, so that
the patient may also be unable to distinguish between mental images and perceptions,
leading to hallucinations and illusions. Usually there is severe anxiety and agitation. When 11
stupor or torpor is established, the patient responds poorly or not at all to stimuli and after
recovery has no recollection of events during the episode. In subacute delirium, there is a
general lowering of awareness and marked incoherence of psychic activity, so that the
patient is bewildered and perplexed. Isolated hallucinations, illusions and delusions may
occur and the level of awareness varies but is lower at night-time. The subacute delirious
state can be regarded as a transitional state between delirium and organic stupor. In twilight
states, consciousness is restricted such that the mind is dominated by a small group of ideas,
attitudes and images. These patients may appear to be perplexed but often their behaviour is
well ordered and they can carry out complex actions. Hallucinations are commonly present.
In organic stupor (torpor), the level of consciousness is generally lowered and the patient
responds poorly or not at all to stimuli. After recovery the patient usually has amnesia for
the events that occurred during the illness episode .
In addition to the above, there are organic syndromes in which consciousness is not
obviously disordered, for example, organic hallucinosis due to alcohol abuse, which is
characterised by hallucinations, most commonly auditory and occurring in clear
consciousness, as distinct from the hallucinations of delirium tremens that occur in
association with clouded consciousness. Amnestic disorders, of which Korsakoff’ s
syndrome is but one, also belong in this group of organic disorders, and are characterised
primarily by the single symptom of memory impairment in a setting of clear consciousness
and in the absence of other cognitive features of dementia.
The chronic organic states include the various dementias, generalised and focal, as
well as the amnestic disorders. Included among the generalised dementias are Lewy body
disease, Alzheimer’ s disease, etc., while the best known focal dementia is frontal lobe
dementia (or syndrome). The latter is associated with a lack of drive, lack of foresight,
inability to plan ahead and an indifference to the feelings of others, although there is no
disorientation. Some patients may also demonstrate a happy-go-lucky carelessness and a
facetious humour, termed Witzelsucht , whereas others are rigid in their thinking and have
difficulty moving from one topic to the next. The most common cause is trauma to the brain
such as those occurring in road traffic accidents. The presence of frontal lobe damage may
be assessed psychologically using the Wisconsin Card Sorting test or the Stroop test.
Amnestic disorders are chronic organic disorders in which there is the single symptom of
memory impairment; if other signs of cognitive impairment are present (such as
disorientation or impaired attention) the diagnosis is dementia. The major neuroanatomical
structures involved are the thalamus, hippocampus, mammillary bodies and the amygdala.
Amnesia is usually the result of bilateral damage, but some cases can occur with unilateral
damage. Further, the left hemisphere appears to be more critical than the right in its genesis
.
Functional Syndromes
Functional syndromes (or disorders), a term seldom used nowadays, refers to those
syndromes in which there is no readily apparent coarse brain disease, although increasingly
it is recognised that some finer variety of brain disease may exist, often at a cellular level.
For many years it was customary to divide these functional mental illnesses into
neuroses and psychoses. The person with neurosis was believed to have insight into his
illness, with only part of the personality involved in the disorder, and to have intact reality
testing. The individual with psychosis, by contrast, was believed to lack insight, had the 12
whole of his personality distorted by the illness and constructed a false environment out of
his distorted subjective experience. Yet such differences are an oversimplification, since
many individuals with neurotic conditions have no insight, and far from accepting their
illness, may minimise or deny it totally, whereas people with schizophrenia may seek help
willingly during or before episodes of relapse. Moreover, personality can be changed
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