Differential stimulant response on attention in children with comorbid anxiety and oppositional defiant disorder.

Attention-deficit hyperactivity disorder (ADHD) affects 3% to 7% of school-age children. Approximately 30% of the children with ADHD also have comorbid anxiety or oppositional defiant disorder. Methylphenidate is the drug of choice for the medical treatment of such cases. When compared with children with ADHD alone, children with comorbid anxiety or oppositional defiant disorder may show worsening of the global attention score in response to methylphenidate and not only a "reduced response," as reported in previous studies. This study included 1122 children diagnosed as ADHD, of which 174 were diagnosed with comorbid anxiety and 141 with comorbid oppositional defiant disorder. All patients performed the Test of Variables of Attention before and after methylphenidate administration. A normal distribution (Gaussian distribution) of reaction to methylphenidate, as measured by the global ADHD score in children diagnosed as pure ADHD, was found. These findings were in contrast to children with ADHD and comorbid anxiety or oppositional defiant disorder who showed a bimodal distribution and hence represent a distinct population. In both groups with comorbid disorders, there was a larger subgroup in which significant worsening of global ADHD score occurred after methylphenidate administration (P < .05). Children with ADHD and comorbid anxiety or oppositional defiant disorder might represent clinically distinct populations in which inattention is secondary to those disorders; therefore, methylphenidate may be an inappropriate treatment for such children.