Organic brain syndromes

Delirium and dementia are the two main types of organic brain syndrome, with focal lesions also to be considered. The term organic brain syndrome means a general disturbance of brain function due to a physical disorder. The characteristic feature is a reduction in intellectual functioning (as tested in mental state examination of orientation, concentration, and memory).

If the disturbance comes on suddenly, as in the context of a very high fever, there will be acute organic brain syndrome, most often referred to as delirium or acute confusional state, with reduced conscious level - drowsiness - as the cardinal feature. If, however, the disturbance comes on gradually, as in dementia due to Alzheimer's disease, the reduction in intellectual functioning will occur in clear consciousness; that is, there is no drowsiness (at least, until the terminal stages). (Dementia could, by extension, be referred to as 'chronic organic brain syndrome', but the phrase is seldom used.)

Localized lesions give rise to focal impairments, such as stroke. This tends to be more the province of neurology. But some types are relevant to psychiatry, and can be considered as psychiatric focal lesions. Examples include Korsakov's psychosis, in which the main abnormality is memory defect; this is due to isolated damage to mesial temporal lobe structures, such as the mammillary bodies. Frontal lobe syndrome (disinhibition, etc.) due to frontal lobe tumour is another example.

Organic brain syndromes are conditions in which psychiatric symptoms result primarily from a biological disorder affecting brain function. This underlying biological disorder may involve structural cerebral pathology and/or metabolic disturbance. The patient's psychological reaction to the illness (see Chapter 11) is also important in organic cases.

DSM-IV does not include the term 'organic brain syndromes' because it is thought to encourage a misleading separation between 'organic' and 'functional' states. DSM-IV uses the concept of 'secondary' disorders instead, but it means essentially the same thing as 'organic' for practical purposes.

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