Objective: To evaluate and compare a focused set of component neuropsychological executive functions in the DSM-IV attention-deficit/hyperactivity disorder combined (ADHD-C) and inattentive (ADHD-I) subtypes.
Method: The Stop task, Tower of London, Stroop task, Trailmaking Test, and output speed measures were completed by 105 boys and girls aged 7-12 classified as either DSM-IV ADHD-C (n = 46), ADHD-I (n = 18), or community control (n = 41).
Results: Both subtypes had deficits on output speed. A group x gender interaction was observed on the Stop task: boys with ADHD-C were impaired versus boys with ADHD-I, whereas girls in the two subtypes did not differ. The ADHD-C type had a deficit in planning. Neither ADHD group had a deficit in interference control per se, although they were slower than controls on the Stroop tasks.
Conclusions: ADHD-I shares neuropsychological deficits with ADHD-C in the domain of output speed; on most domains the subtypes did not differ. Neuropsychological distinctions between these ADHD subtypes may be few, depending on which domain of executive functioning is assessed, and these distinctions differ by gender. In the case of boys, the two subtypes may be distinguished by the specificity of motor inhibition deficits to ADHD-C.