Hyperactivity and comorbidity in Japanese children with attention-deficit/hyperactivity disorder.

No previous study about comorbidity of attention-deficit/hyperactivity disorder (ADHD) in Japan have carried out both a comprehensive investigation using a structured interview and a comparison between ADHD subtypes. The aim of the present study was to clarify the relationship between hyperactivity and disruptive behavior disorder (DBD) in ADHD by comparing a hyperactivity group (HG) with a non-hyperactivity group (non-HG). After diagnosis was carried out by strict exclusion, the 41 ADHD subjects (6-14 years old; IQ, 70-121) diagnosed according to DSM-IV were divided into HG (n = 24) and non-HG (n = 17), and compared for comorbidities and psychopathologies. This was done via semistructured interview with children and parents and questionnaires to parents and teachers. The results demonstrate that (i) most ADHD children had comorbidity (e.g. DBD or anxiety disorder); (ii) the HG had a significantly higher rate of DBD than the non-HG, but the total number of anxiety disorders was not different between subgroups, and (iii) the HG generally had more serious psychopathologies both at home and at school than the non-HG. Both groups had more serious externalizing and internalizing problems at home than at school. The present study provides evidence of a strong relationship between hyperactivity and DBD.