In considering potential explanations for the co-occurrence of PBD with ADHD, it was proposed that the presence of PBD symptoms could lead to an artificial increase in diagnostic rates for PBD in ADHD samples, and that ADHD could be an early and prodromal manifestation of PBD. This proposition was then linked with the findings on treatment-emergent mania - mania triggered by pharmacological treatment with stimulants and/or antidepressants.16
Following this, it was proposed that ADHD and its associated factors, such as treatment with stimulants, may induce PBD symptoms, and that PBD and ADHD could have an underlying common etiology as regards genetic and neurobiological risk factors.15
In a recent review analysis, Singh et al have provided evidence that individuals at risk of developing ADHD symptoms may represent early prodromal states of PBD, and that PBD with comorbid ADHD may constitute a particular phenotype of early-onset disturbed mood and impaired affective regulation referred to as early PBD.16
However, these findings are far from definite, and the extent of comorbidity and the severity of symptom overlap between ADHD and PBD is not yet clear. Moreover, there are also nonoverlapping symptoms, as depicted in ().
Figure 3. DSM-IV symptoms of attention deficit-hyperactivity disorder and bipolar mania not showing an overlap. Adapted from ref 23: Wingo AP, Ghaemi SN. A systematic review of rates in diagnostic validity of comorbid adult attention-deficit/hyperactivity disorder (more ...)
Clarification on these issues is handicapped by the lack of longitudinal data on developmental processes in juvenile PB D, which can in part be put down to problems of feasibility in investigations, one of which constitutes patient recruitment for follow-up measures.
In research, the Child Behavior Checklist (CBCL) has frequently been implemented as a tool for the diagnosis of PBD. Biederman and colleagues introduced a particular profile within the CBCL characterized by elevated scale-values of “Anxiousness/Depressiveness,” “Attention Problems,” and “Aggression” scores discriminating children with a diagnosis of PBD from those with ADHD and those without ADHD or PBD.16,17
A CBCL-PBD score can be produced from the sum of all three aforementioned CBCL subscales, with a score of >225 predicting PBD with a specifity of 97%.18-20
It is noteworthy that longitudinal data investigating the contextual framework of the CBCL-PBD profile produce only limited evidence of the stability and outcome of this pattern at the current stage. A recent study investigating the diagnostic and functional trajectories of individuals with the CBCL-PBD phenotype from early childhood through to young adulthood showed that individuals matching the outlined CBCL-PBD phenotype displayed increased rates of suicidal thoughts and behaviors and psychosocial impairments, and an increased risk of comorbid anxiety, bipolar disorder, ADHD in young adulthood, and cluster B personality disorders.22
However, diagnostic accuracy was low for each of the outlined disorders, suggesting that the CBCL-PBD phenotype has a stronger predictive value for the classification of impairments and comorbid symptoms but is weaker in predicting a particular diagnosis.21
This finding is particularly instructive, as observed symptom patterns represented in the CBCL do not represent distinct clinical diagnoses (ie, as outlined in DSM-IV). To a certain extent this CBCL-PBD profile preponderance of aggregated and overt symptoms related to a variety of disorders may be due to the contextual diversity of symptoms which explain differing amounts of variance to their respective disorders. This again underlines the need for ongoing longitudinal research on the CBCL-PBD profile and other operationally defined diagnostic and psychometric measures.
However, it is noteworthy that symptoms shown in the CBCL-PBD profile - such as problems with attention and aggressive behavior - are ambiguous. Moreover, in the realm of affective symptoms only the depressive states in mood swings get some representation in the CBCL-PBD score, which in turn raises the possibility of potential manic mood swings being underrepresented within the CBCL-PBD profile and not being covered by elevated scores of attention problems.
The comorbidity of ADHD and BD in adults has also been the subject of recent research. The overlap of ADHD symptoms with those of bipolar mania such as increased activity, restlessness, and increased and rapid talking may also interfere with the process of obtaining a differential diagnosis between these two disorders. However, because of this the diagnosis of manic states in children and juveniles is frequently difficult,12
so that at this stage the transfer of findings related to the ADHD/BD comorbidity in adults and their application to juveniles is highly problematic. Despite this diagnostic, developmental, and phenomenological dilemma, some major differences between ADHD and BD in adults mentioned by Wingo and Ghaemi should be taken into consideration on the grounds that ADHD symptoms tend to be chronic characteristics, whilst bipolar mania refers to episodic states.22
This specific finding deserves careful consideration, once again emphasizing the need for ongoing longitudinal studies in populations of children and adolescents at risk for severe mood dysregulation. Moreover, in contrast to mania in adult patients with BD, productivity in patients with ADHD may not be improved, as indexed by problems in daily working life. Sleep disturbances would also be more likely to be observed in bipolar patients.22
Here again, in similarity to children and juveniles, it has been argued that treatment of ADHD with comorbid BD is challenging, in that treatment-emergent mania and the exacerbation of bipolar symptoms can occur while receiving treatment with stimulants.22
A recent review article22
comprising four studies examining phenomenological aspects of ADHD and BD in adults detected two significant levels of overlap between these two disorders.22,26
One level was based on the overlap in DSM-IV symptoms for ADHD (ic, excessive talking, difficulties in sustaining attention or remaining seated, blurting out answers before questions have been completed, etc).22
A second level identified an overlap between ADHD symptoms and bipolar mania, indexed by excessive talking in bipolar mania and to a lesser extent in ADHD,distractibility in BD as opposed to difficulties in sustaining attention in ADHD, and increased activity and physical restlessness in BD as opposed to hypcrmotoric behavior in ADHD (for a summary see Wingo and Ghaemi22
). Two studies examining the course of illness found an earlier age of onset in adults with ADHD and comorbid BD compared with subjects with a single diagnosis of adult BD.24,25
In consequence, studies investigating the overlap in clinical symptom patterns of PBD and ADHD should focus on potential developmental changes demanding large longitudinal investigations from childhood through adolescence to later adulthood.