Effects of methylphenidate on subtypes of attention-deficit/hyperactivity disorder.

OBJECTIVE: To compare the effects of methylphenidate on attention-deficit/hyperactivity disorder (ADHD) subtypes. METHOD: Nineteen ADHD/inattentive (ADHD/I) and 22 ADHD/combined (ADHD/C) 6- to 12-year-old children entered a 6-week, double-blind trial of placebo and methylphenidate in divided doses (0.94 +/- 0.02 mg/kg/day = 33.06 +/- 1.40 mg/day). ADHD children received a restricted arithmetic task without medication before the trial and after their noon dose on the last day of each phase. Thirty-four unmedicated controls were tested at comparable time points. Parents and teachers rated ADHD children before and after each phase of the trial; parents rated controls before the study. RESULTS: Controls had marginally better arithmetic performance than children with ADHD/C who outperformed ADHD/I children. Unmedicated children with ADHD exceeded controls in task-incompatible behaviors during restricted arithmetic. Under methylphenidate, both ADHD subtypes reached control levels of arithmetic performance and task-incompatible behavior. Before the trial, parents rated children with both ADHD subtypes higher than controls on inattention, hyperactivity, and oppositionality/aggression and parents and teachers rated ADHD/C children higher than ADHD/I children on hyperactivity and oppositionality/aggression but not inattention. Methylphenidate lowered parent and teacher ratings of inattention and hyperactivity for those with both ADHD subtypes, but ratings of children with ADHD/C decreased more in hyperactivity and aggression. CONCLUSIONS: Methylphenidate ameliorated task-incompatible behavior, arithmetic performance, and inattention comparably in both ADHD subtypes, whereas medication reduced hyperactivity and aggression largely in children with ADHD/C.

Performance and private speech of children with attention-deficit/hyperactivity disorder while taking the Tower of Hanoi test: effects of depth of search, diagnostic subtype, and methylphenidate.

We administered the Tower of Hanoi to demographically comparable samples of control participants (n = 34) and children with the Combined (n = 22) and Inattentive subtypes (n = 19) of Attention-Deficit/Hyperactivity Disorder (ADHD). Controls excelled over children with the Inattentive subtype, who outperformed patients with the Combined subtype. These results replicated findings of greater executive deficits in the Combined than in the Inattentive type of ADHD. Double-blind administration of methylphenidate improved task performance only for patients with the Inattentive subtype. In a drug-free Baseline session, children with both subtypes of ADHD made more private verbalizations than controls, particularly when failing puzzles. In later sessions, regardless of drug condition, the inattentive sample exhibited a smaller increase in self-regulatory utterances under failure. In contrast, the combined sample decreased self-regulatory verbalizations under failure only under methylphenidate. The results support some differences between the two subtypes of ADHD in executive functioning and in their response to stimulant therapy.