Impulsivity and compulsivity may appear to be at opposite ends of the spectrum of behavior disorders. Whereas impulsivity implies acting without forethought, compulsivity is acting after too much thought or an obsession. However, both impulsivity and compulsivity share an inability to inhibit a potentially harmful behavior in response to a stimulus, whether it is internal or external.

The existence of intermittent explosive disorder as a unique entity remains controversial. Many have difficulty with the idea of a normal baseline with superimposed periods of aggressive episodes. In addition, anger outbursts are a part of many other disease entities. Intermittent explosive disorder is thought to be rare (not common) and occurs more frequently in males. High rates of fire-setting behavior in persons with the disorder have been reported. Recent studies suggest higher than normal rates of intermittent explosive disorder in families of patients with the diagnosis. First-degree relatives of patients with the disorder appear to have higher (not lower) than expected rates of depressive disorders and alcohol and substance abuse. Typical patients appear to be large (not small) men with dependent (not avoidant) personality features who respond to feelings of uselessness or impotence with violent outbursts.

Modest neurobiological studies point to possible deranged serotonin neurotransmission in patients identified with intermittent explosive disorder; low cerebrospinal fluid (CSF) levels of 5-hydroxyindoleacetic acid (5-HIAA) in some impulsive, temper-prone individuals; and lowered levels of platelet serotonin reuptake in patients with episodic rage. A connection has also been inferred between elevated CSF testosterone levels and aggressive or openly violent behavior. An element of genetic loading is also suggested by the fact that blood relatives are more likely to have characteristic outbursts of explosive behavior compared with adoptive relatives. Increased glucose metabolism has not been implicated in patients with abnormal aggression.

Although research has been limited, it is generally assumed that intermittent explosive disorder—similar to other impulse-control disturbances—is caused by a varying confluence of psychosocial and neurobiological factors. Patients regularly describe chaotic family backgrounds, rife with explosive behavior and verbal and physical abuse, often in the context of acute alcohol intoxication. Identification with the aggressor is a common defense mechanism, in which the explosive violence of a parent or close relative is internalized. This sinister coping strategy replicates the acts of stormy violence to which patients have been exposed during their formative years. Situations that realistically or symbolically evoke memories of early oppression and trauma may spark explosive episodes. Typically, an acute sense of narcissistic injury, lowered self-esteem, and profound feelings of shame and humiliation are evoked.

Passive-aggressive behavior is aggression toward an object expressed indirectly and ineffectively through passivity, masochism, and turning against the self. Regression is a return to a previous stage of development or functioning to avoid the anxieties involved in later stages. Controlling is the excessive attempt to manage events or objects in the environment in the interest of minimizing anxiety and solving internal conflicts. Reaction formation is the management of unacceptable impulses by permitting expression of the impulse in an antithetical form.

Serotonergic neurons (not dopaminergic neurons) mediate behavioral inhibition. Decreases in serotonergic transmission can reduce the effect of punishment as a deterrent of behavior, and the restoration of serotonin activity restores the behavioral effect of punishment. Researchers have suggested a connection between low levels of CSF and 5-HIAA and impulsive behavior. Patients with intermittent explosive disorder are typically large, dependent men with a poor sense of masculine identity. Patients may feel helpless before an episode. A predisposing factor in childhood is encephalitis, as are perinatal trauma, minimal brain dysfunction, and hyperactivity. A patient’s childhood was often violent and traumatic. Neurological examination can show left–right ambivalence and perceptual reversal. The disorder usually grows less severe with age, but heightened organic impairment can lead to frequent and severe episodes.