We have investigated the longitudinal course of ODD in girls with ADHD outside the context of CD. At the 5-year follow-up assessment into adolescence, ODD at baseline predicted a significantly increased risk for ODD and major depression at follow-up beyond the risk conferred by ADHD alone. These findings expand on previous results from longitudinal studies of girls with ADHD6,22
by identifying the risks associated with comorbid ODD.
Our findings documenting that ODD (in the absence of CD) in girls with ADHD selectively increases the risks for ODD and major depression are highly consistent with our recently reported findings in a sample of boys with ADHD followed longitudinally over 10 years into young adult years.3
These findings are also consistent with results reported by Greene and colleagues8
in a cross-sectional pediatric sample that also found a strong association between ODD and MDD. These findings are also consistent with those recently reported by Brotman and colleagues23
on the longitudinal course of children with “chronic irritability and hyperarousal” (also termed severe mood dysregulation or “SMD”) largely comprising youth with ADHD and ODD. In addition, our post-hoc test by age group suggests that early onset ODD may be a more potent risk factor for MDD in adolescence.
Although not statistically significant, the finding that both ADHD and ODD in girls increased the risk for CD at the adolescent follow up is consistent with our previous longitudinal study of boys with ADHD as well as other studies in the literature. While some longitudinal prospective studies of clinic-referred children suggested that childhood ADHD predicts later antisocial behavior,24,25
others suggested that childhood ADHD only appears to be a risk factor for adolescent CD when childhood disruptive behavior problems are also present.26,27
For example, in this study of girls with ADHD, as well as in our previous study of boys with ADHD, the risk for CD was larger when comorbid with ODD (24% versus 10% in girls, p=0.06). More definitive conclusions as to the nature of the association between ADHD, ODD, CD, and antisocial personality disorder in girls with ADHD await longer follow-up studies and studies that include a sufficiently powered sample of girls with CD.
Although the finding that both ADHD and ODD increased the risk for bipolar disorder are consistent with an emerging literature linking these three disorders,28,29
they are discrepant with the findings reported in our longitudinal study of boys with ADHD grown up, showing that the risk for bipolar disorder was selectively associated with CD.30
It is noteworthy however that the risk for bipolar disorder was larger in girls with ADHD with comorbid ODD compared to those without this comorbidity (24% versus 10%, p=0.06). More work is needed with longer follow-up studies to better understand the nature of the association between ADHD, ODD, and subsequent bipolar disorder in girls with ADHD.
While we did not find a difference among the groups for PSUD and the apparent differences for smoking did not survive adjustment for multiple comparisons (p=0.01), the sample was still young at follow-up (average age=16.6 years). Additional follow-ups are needed to understand the relationship between ADHD, ODD, and substance use.
Our CBCL results showing that girls with ADHD with comorbid ODD could be distinguished from other girls with ADHD without ODD by their more severe CBCL profile are consistent with our previous findings in boys with ADHD. Equally important is the result showing that at follow-up, girls with ADHD plus ODD selectively differed from other girls with ADHD without ODD on the CBCL Aggressive Behavior and Delinquent scales, scales previously shown to correspond to structured interview derived diagnoses of ODD32
It is also noteworthy that this profile of elevations of the Aggressive and Delinquent scales of the CBCL is the same as was previously identified in a sample of boys as being predictive of boys with ODD who subsequently developed CD at the 10-year follow-up. If these results are confirmed in future follow-up studies, the ability to distinguish girls ODD at higher risk to develop subsequent CD by their CBCL profile is of high clinical and public health significance.
While ODD increased the risk for major depression at follow-up, ODD was not associated with a higher score on the CBCL Anxious/Depressed scale. The inclusion of anxiety questions in the Anxious/Depressed scale may explain why an effect was not found, because ODD was not associated with multiple anxiety disorders at follow-up. In addition, the Anxious/Depressed scale contains primarily symptoms about depressed mood (e.g., cries, worthless, sad), and it is possibility that subjects with ODD tend to have a more symptoms related to an irritable or cranky mood. Further work is needed to answer this question.
Further evidence for a compromised course associated with the comorbidity of ODD in girls with ADHD can be seen in the findings that this comorbidity predicted a higher likelihood of placement in special classes and school suspension. The compromised course associated with ODD in girls with ADHD is consistent with findings from a recent study by Harpold and colleagues35
in adults with ADHD. This study found that 30% of referred adults with ADHD and comorbid ODD in childhood continued to have ODD in adulthood regardless of comorbid CD, and adults with ODD were also at risk for more compromised outcomes.
Our findings need to be considered in light of some methodological limitations. Because our sample was referred, results may not generalize to girls with ADHD in the general population. Referred cases have been described as having potentially differing clinical characteristics (e.g., chronic course, high comorbidity) from cases in the population.36
However, our results are likely to generalize to girls with ADHD seen in pediatric and psychiatric settings. Likewise, since our sample was largely Caucasian, results may not generalize to other minority groups.
The wide age range of subjects covered a broad developmental spectrum. Samples with narrower age ranges followed over time may be more suited to studying developmental trajectories in childhood and adolescence. The rates of disorders reported here might differ from other studies that use subjects at different developmental stages. Although younger subjects were more likely to have ADHD (p=0.02) and ODD (p=0.003) at follow-up, and older subjects were more likely to have PSUD and smoking at follow-up (both p<0.001), our comparisons are valid because the groups did not significantly differ by age.
We did not conduct direct comparisons of our boys' and girls' samples because the boys' sample was several years older and therefore we would be unable to disentangle age and gender effects. The statements above comparing the boys' and girls' results should be viewed cautiously until direct statistical comparisons can determine gender differences using future follow-up assessments of these samples.
While our results show a significant association between ODD and subsequent morbidity, we cannot rule out the possibility that other correlates of ODD (e.g., poor family functioning) are the primary cause of subsequent morbidity (e.g., depression). Future studies that examine multiple risk factors in addition to disruptive behavior disorders may shed light on such hypotheses.
Despite these limitations, this systematic investigation of the longitudinal course of ODD in girls with ADHD documents that this comorbidity is associated with significant additional morbidity and disability than that associated with ADHD alone, even in the absence of CD. More definitive conclusions await subsequent research with larger samples of ADHD and ODD in the absence of CD followed for a more extended period of time.