Adult ADHD and its comorbidities, with a focus on bipolar disorder

Attention deficit hyperactivity disorder (ADHD) is a syndrome that most often presents in childhood. However, the condition is also relatively common in adults, with prevalence rates reaching 5% in the general population, with more than half the children affected by ADHD retaining the condition during their adult years. While the disorder in children is most often described as a disorder involving hyperactivity and impulsiveness, ADHD presents with very different characteristics in adulthood, notably with less externalizing symptoms and with a higher rate of psychiatric comorbidities, including major depressive disorder, bipolar disorder (BD), anxiety disorders and substance abuse. This review will focus on the evidence relating to bipolar disorder BD and its potential link with ADHD, looking at epidemiological, familial and neuroimaging studies. The comorbid presentation of people suffering with ADHD and BD (ADHD/BD) is associated with a more severe disease course, more severe mood disorder symptoms, and lower functional scores. Importantly, the co-segregation of these two conditions makes ADHD diagnosis challenging because its symptoms are often mistakenly assumed to be part of BD. As a result, patients with comorbid ADHD/BD are under-diagnosed and under-treated. Optimal diagnosis, understanding and treatment of the comorbid condition are important, as ADHD/BD has been associated with significant functional impairment and suboptimal treatment responses when compared to ADHD or BD populations alone.