Comorbidity of attention-deficit/hyperactivity disorder with psychiatric disorder: an overview.

Attention-deficit/hyperactivity disorder (ADHD) has been noted to be comorbid with a variety of psychiatric disorders. These include oppositional defiant and conduct disorders, as well as affective, anxiety, and learning disorders. Considerable debate has revolved as to the meaning of this overlap. Does it occur by chance or is it an artifact of referral bias? Are the comorbid conditions secondary to the ADHD, or can other psychiatric disorders masquerade as attentional problems? Alternatively, ADHD may exist as distinct subtypes, each with its specific comorbidity. Studies that have examined the comorbidity of oppositional, conduct, affective, anxiety, and learning disorders in ADHD are reviewed. ADHD and ADHD with conduct disorder appear to be distinct subtypes, possibly with different etiologies. While the short-term response to stimulants is the same in these two groups, children with ADHD and conduct disorder children have higher rates of antisocial personality as adults. Coexisting anxiety appears to attenuate impulsivity in ADHD, and stimulant response is poorer in ADHD children with comorbid anxiety. Anxiety and ADHD appear to be inherited independently. A subset of ADHD children also meet criteria for bipolar disorder, although the exact prevalence of this diagnosis in ADHD children is strongly debated. Regardless of prevalence, this is a severely impaired group of ADHD children, with high rates of aggression and psychiatric disorder in their families. The comorbidity of ADHD and major depression is much less studied, and few firm conclusions can be made about it. Finally, about 20%-25% of ADHD children meet criteria for a learning disorder, but learning disorders appear to be independent of ADHD.