The results of the NIMH Collaborative Multisite Multimodal Treatment Study of Children with Attention-Deficit/Hyperactivity Disorder (MTA) have been reexamined from several standpoints. One panel of investigators has examined whether core symptoms (inattention and impulsivity) and symptom profiles differ as a function of comorbidity and gender. A continuous performance task (CPT) and rating scales were used to measure core symptoms in 498 children from the MTA who were divided into 4 groups. CPT inattention, impulsivity, and dyscontrol errors were high in all groups. Children with ADHD + anxiety disorders (internalizing symptoms) were more inattentive than impulsive, whereas those with ADHD + ODD or CD (externalizing symptoms) were more impulsive than inattentive. Girls were generally less impaired and less impulsive than boys, and girls with ADHD + anxiety made fewer CPT impulsivity errors than girls with ADHD only. 
COMMENT. Despite differences in symptomatology, children with ADHD and comorbid symptoms have high levels of objectively measured ADHD core symptoms. Girls are generally less affected and show less impulsivity than boys, especially when ADHD is comorbid with anxiety symptoms. These findings have treatment implications, since medication may be less frequently required in girls with low levels of impulsivity.
Comparison of ADHD comorbid subgroups. The MTA data were analysed using validational criteria to compare ADHD subgroups, with and without comorbid anxiety and ODD/CD. Children with ADHD-only or ADHD + ODD/CD (without anxiety) responded best to medication treatments (with or without behavioral treatments), while those with multiple comorbidity (anxiety and ODD/CD) responded best to medication and behavioral treatments combined. Children with ADHD + anxiety (without ODD/CD) responded equally well to the MTA behavioral and medication treatments. The authors conclude that the clinical comorbid profiles are sufficiently distinct to warrant classification as ADHD subtypes. 
Treatment success rates. Optimal responses on the MTA/ADHD rating scales are obtained with combined treatments (68%), followed closely by medication alone (56%), then behavioral therapy (34%), and finally, community care (25%).