To further clarify the relationship between childhood ADHD and adolescent aggression, this study sought to compare overt aggression, anger, and hostility in adolescents initially diagnosed with childhood ADHD-only, ADHD + ODD, and ADHD + CD. These three groups were compared to each other and to a non-ADHD control group recruited in adolescence. This study further examined adolescent aggression, anger, and hostility as a function of the persistence of ADHD into adolescence as rated by parents and adolescents.
Initial analyses indicated that, in individuals diagnosed with ADHD, the presence of a comorbid DBD in childhood is associated with differences in overt aggression in adolescence. Individuals diagnosed with ADHD+CD were found to have significant elevations on a measure of physical aggression when compared to Controls and those who had ADHD only, while individuals diagnosed with ADHD+ODD displayed significant elevations on a measure of verbal aggression compared to Controls. Additionally, both comorbid groups differed from Controls on multiple measures of anger. Reanalysis of the data controlling for differences in Verbal IQ did not affect findings on any dependent measures. This study did not find significant group differences on a measure of hostility, suggesting that the elevated rates of overt aggression were more related to underlying emotional rather than cognitive processes.
As expected, those with childhood ADHD had significantly higher levels of ADHD symptoms in adolescence as compared to Controls. However, the ADHD-only, ADHD+ODD and ADHD+CD groups, as defined during childhood, did not differ significantly in severity of ADHD symptoms during adolescence. Reanalysis of the data controlling for adolescent ADHD symptom severity (or persistence), did not affect findings with regard to physical aggression, which was still elevated in those with childhood CD. However, adolescent ADHD status accounted for group differences on measures of verbal aggression and anger.
The results of this study support previous findings in the literature that among individuals diagnosed with ADHD in childhood, later physical aggression is best explained by comorbid CD. However, our results also indicate that elevations in verbal aggression and anger are best explained by the persistence of ADHD symptoms and not childhood comorbidity.
That persistence of ADHD symptoms explained significant differences initially seen among comorbid groups on measures of anger on both the AQ and STAXI-2 strengthens the argument that ADHD is associated with increased emotionality. While this is not considered a core symptom of the disorder, it is frequently noted to be present, and is often a target of treatment in older patients with ADHD [37
]. Such interventions range from treatment with anti-epileptic and antipsychotic medications targeting mood regulation to an array of cognitive-behavioral/psychotherapeutic treatments [38
]. Further, the experience of angry feelings in adolescents with ADHD appeared to be stable and persistent, suggesting that anger in adolescents with persistent ADHD is a trait behavior, rather than an acute, or intermittent state. Consistent with these findings of emotional dysregulation in adolescents with childhood ADHD, recent data suggest elevated rates of Cluster B personality disorders among adults with ADHD [40
]. As such, it is possible that this emotional dysregulation contributes to the well-documented functional impairment that characterizes the adult outcome of so many individuals with ADHD [42
Interestingly, significant group differences were not seen on measures of hostility. This is surprising given that research in social cognitive learning theory has shown hostile attributional biases to exist in children displaying reactive but not proactive aggressive behaviors. While this study did not distinguish between proactive and reactive aggressive behaviors, it is likely that both forms of aggression were represented in our sample. Waschbusch and colleagues [44
] showed that boys diagnosed with multiple DBDs were more highly reactive to provocation when compared to normal and non-comorbid peers. However, other studies have not found significantly high levels of hostility in boys meeting criteria for ODD or CD [45
] As these relationships are currently unclear, future studies may wish to further explore the association between reactive and proactive aggression, hostility, and their association with childhood disruptive behavior disorders.
These findings must be viewed within the context of some study limitations. Perhaps most importantly, is the disparity in sample size that existed between groups. The relatively low number of individuals diagnosed with ADHD alone limited the power to detect differences specifically related to this group. Additionally, that this study was conducted in a large metropolitan area with most participants being male, may limit the generalizability of these findings. Due to the small number of females in the sample, it is likely that our findings primarily reflect the emotional dysregulation associated with ADHD and aggression in males. Our sample was not adequate for a systematic evaluation of gender effects. It is quite possible that findings would be different in females in that several studies have suggested that females express their aggression differently from males. Whereas young boys and adolescents are often described as impulsive and physically aggressive, aggression in girls is more typically described as less direct and more socially ostracizing and isolating [47
]. Finally, it is notable that all of our primary dependent measures were in the form of self-report. Had parental or spousal report been used, it is possible that findings would not be identical. Finally, the fact that many of the original participants were lost to follow-up is potentially problematic; however, because the included sample did not differ on any childhood ratings from those that were lost to follow-up, it is likely that they are representative of the original group.
Overall, this study examined the self-reported expression of overt aggressive behaviors, covert emotional and cognitive processes, and the influence of the progression of ADHD symptoms in adolescents diagnosed with ADHD and comorbid disruptive behavior disorders during childhood. A systematic progression of analyses resulted in significant differences among both comorbid groups on measures of physical and verbal aggression and anger when compared to Controls. Adolescent ADHD symptomatology was found to account for differences in verbal aggression and anger, but not physical aggression, which was significantly associated with a comorbid diagnosis of CD. These results indicate that, in adolescents diagnosed with ADHD during childhood, aggression is not purely a function of comorbidity, but is mediated, in part, by the emotional experience of anger, which is associated with the persistence of ADHD symptoms into adolescence. These findings suggest that in addition to inattention and hyperactivity/impulsivity, emotional dysregulation may be an important component of ADHD and should be considered when making diagnoses. Additionally,findings further indicate that treatments targeting emotional liability may be appropriate for those with and without comorbid DBDs.