A comparison of the neuropsychological profiles of the DSM-IV subtypes of ADHD

Recent research on the DSM-IV subtypes of attention-deficit/hyperactivity d isorder (ADHD) has demonstrated that the subtypes differ in demographic cha racteristics, types of functional impairment, and profiles of comorbidity w ith other childhood disorders. However, little research has tested whether the subtypes differ in underlying neuropsychological deficits. This study c ompared the neuropsychological profiles of children without ADHD (n = 82) a nd children who met symptom criteria for DSM-IV Predominantly Inattentive s ubtype (ADHD-IA; n = 67), Predominantly Hyperactive Impulsive subtype (ADHD -HI; n = 14), and Combined subtype (ADHD-C; n = 33) in the areas of process ing speed, vigilance, and inhibition. We hypothesized that children with el evations of inattention symptoms (ADHD-IA and ADHD-C) would be impaired on measures of vigilance and processing speed, whereas children with significa nt hyperactivity/impulsivity (ADHD-HI and ADHD-C) would be impaired on meas ures of inhibition. Contrary to prediction, symptoms of inattention best pr edicted performance on all dependent measures, and ADHD-IA and ADHD-C child ren had similar profiles of impairment. In contrast, children with ADHD-HI were not significantly impaired on any dependent measures once subclinical symptoms of inattention were controlled. Our results do not support distinc t neuropsychological deficits in ADHD-IA and ADHD-C children, and suggest t hat symptoms of inattention, rather than symptoms of hyperactivity/impulsiv ity, are associated with neuropsychological impairment.