A change in personality is likely to follow diffuse, severe damage to the brain of the sort that is commonly seen after major head injury, but which can also occur in association with cerebral tumours, cerebrovascular disease, dementias, and encephalitis. The changes in behaviour are persistent and often develop gradually, but they may lead to sudden outbursts of impulsivity which create acute problems. A survey of patients who had survived a severe head injury reported that the prevalence of personality change increased with time; at five years after the injury, 74% of patients were described by their relatives as having undergone a personality change. Threats or gestures of violence had occurred in 54% while there had been an actual assault on a relative in 20% of cases. Other problems which had occurred included trouble with the law (31%), childishness (38%), and being upset by minor changes in routine (38%).56
Brain injury can produce an exaggeration of premorbid personality traits so that a person with an obsessional personality becomes even more meticulous and preoccupied with detail, whereas someone with an antisocial personality becomes more impulsive, irresponsible, and aggressive. Among a group of patients with Wilson's disease, psychopathic personality traits were significantly related to the severity of neurological symptoms, particularly dysarthria, bradykinesia, and rigidity.57 If the damage is localised to particular parts of the brain, the personality changes tend to be more specific.58,59 Frontal lobe damage is associated with apathy, lack of initiative, tactlessness, irritability, euphoria, and disinhibition. Although the patient's demeanour is predominantly listless there may be unpredictable outbursts of aggression or sexually disinhibited behaviour. Social skills tend to be lost with a failure to consider the feelings of other people and the impact of tactless remarks. The ability to plan ahead is impaired, with the result that irresponsible decisions may be taken with little concern about their outcome.
Irritability and aggressive outbursts are especially associated with temporal lobe pathology. Herpes simplex encephalitis has an affinity for the temporal lobes, so behavioural manifestations are common during the acute stages of the illness and after recovery if there is residual brain damage. Patients who survive temporal lobe damage may manifest the features of the KlUver-Bucy syndrome which include hypersexuality, aggressive outbursts, excessive oral behaviour, and visual agnosia.
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