The impulse dyscontrol and aggression syndrome consists of an inability to resist an impulse to perform a harmful act; the impulse is accompanied by a buildup of tension needing to be released, and is followed by a feeling of satisfaction or relief when the act is committed. This in turn is followed by either relief, remorse, or a sense of justification for the act. Impulse dyscontrol and aggression can occur in neurologically normal individuals, but this behavior becomes pathological when carrying out the impulse consistently harms the subject or others. These behaviors may occur in patients with psychiatric disorders and global or localized brain dysfunction.
A number of other neuropsychiatric conditions may be associated with aggression. In patients with psychotic disorders, such as those mentioned earlier, aggressiveness may be a component. This type of behavior may also be seen with manic episodes and usually arises from delusional beliefs. A primary psychiatric disorder known as intermittent explosive disorder is characterized by discrete episodes of unrestrained violence that result in serious assaultive acts or destruction of property. The degree of aggressiveness is grossly out of proportion to any precipitating psychosocial stressors, occurs in a person with a clear consciousness, and is not accounted for by another mental disorder or the direct effects of a substance or any medical or neurological condition. Although the etiology of this disorder is unknown, investigations have suggested that disordered limbic system function with decreases in serotonergic transmission may play an important role.
Aggression may occur in patients with other medical or neurological conditions, producing global brain dysfunction. With a reduced level of consciousness and altered sleep-wake cycles, patients with delirium (due to electrolyte derangements, infection, drugs, or postsurgical or postictal conditions) may experience transitory ill-formed delusions and misperceptions leading to aggression. Encephalitis secondary to herpes simplex virus can become manifest with aggressiveness and may be associated with memory difficulties, irritability, distractibility, apathy, and restlessness. Childhood attention-deficit disorder, although it becomes manifest generally with attentional impairment, may be associated with destructive behavior when it is severe. Self-mutilation in association with aggression is a prominent feature of both the Lesch-Nyhan and the Prader-Willi syndromes, and may be seen in any condition that causes mental retardation. Finally, aggression in the context of a general personality change may be seen in patients with global neurodegenerative disorders such as Alzheimer's disease and Huntington's disease. When more prominent frontal lobe involvement is present, as occurs in the frontal lobe dementias, explosive outbursts of rage may be seen. Focal frontal lobe dysfunction in the presence of head
injury, tumors, or stroke may lead to disinhibited behavior and a need to do things on the spur of the moment. Disinhibited behaviors accompanied by a lack of restraint of antisocial impulses but without aggression can occur in patients with orbitofrontal damage. Aggressive impulses in the form of rage in response to trivial irritations may arise in patients with dorsolateral prefrontal damage. Limbic system dysfunction, particularly with involvement of the ventromedial hypothalamus or amygdala, in which the affective significance of stimuli may be altered, may also be associated with rage and violent behavior. This condition typically occurs in patients with amnesia, hyperphagia, and other evidence of hypothalamic dysfunction and is usually associated with neoplastic invasion. Occasionally, impulsive behavior, aggressiveness, or just inappropriate behavior is ascribed to seizures of temporal lobe onset, but complex behaviors involving directed interactions with other individuals is rarely of convulsive origin.
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