Objectives: Pediatric bipolar disorder (BPD) and attention-deficit hyperactivity disorder (ADHD) co-occur more frequently than expected by chance. In this review, we examine 4 potential explanations for the high rate of this common co-occurrence: (i) BPD symptom expression leads to overdiagnosis of ADHD in BPD youth; (ii) ADHD is a prodromal or early manifestation of pediatric-onset BPD; (iii) ADHD and associated factors (e.g., psychostimulants) lead to the onset of pediatric BPD; and (iv) ADHD and BPD share an underlying biological etiology (i.e., a common familial or genetic risk or underlying neurophysiology).
Methods: Peer-reviewed publications of studies of children and adolescents with comorbid BPD and ADHD were reviewed.
Results: There is a bidirectional overlap between BPD and ADHD in youth, with high rates of ADHD present in children with BPD (up to 85%), and elevated rates of BPD in children with ADHD (up to 22%). Phenomenologic, genetic, family, neuroimaging, and treatment studies revealed that BPD and ADHD have both common and distinct characteristics. While there are data to support all 4 explanations postulated in this paper, the literature most strongly suggests that ADHD symptoms represent a prodromal or early manifestation of pediatric-onset BPD in certain at-risk individuals. Bipolar disorder with comorbid ADHD may thus represent a developmentally specific phenotype of early-onset BPD.
Conclusions: The etiology of comorbid BPD and ADHD is likely multifactorial. Additional longitudinal and biological studies are warranted to clarify the relationships between BPD and ADHD since they may have important diagnostic and treatment implications.