Gender Differences in the Behavioral Symptoms and Neuropsychological Performance of Patients with Attention-Deficit/Hyperactivity Disorder Treated with Methylphenidate: A Two-Year Follow-up Study

Objective: This study investigated the gender differences in behavioral symptoms, as rated by various informants, and in neuropsychological performance, among patients with attention-deficit/hyperactivity disorder (ADHD) treated with methylphenidate during 24 months in a clinical setting. Methods: Study participants comprised 128 boys (mean age: 13.22.4 years) and 26 girls (mean age: 12.81.0 years) with ADHD. All patients were prescribed short-acting oral methylphenidate, taken two or three times daily; each dose ranged between 0.3 and 1.0mg/kg. At the baseline and 6, 12, 18, and 24 months later, behavioral symptoms were evaluated using the parent and teacher forms of the Swanson, Nolan, and Pelham Version IV (SNAP-IV) scale for ADHD and the ADHD Rating Scale (completed by a child psychiatrist). In addition, neuropsychological function was assessed using the Test of Variables of Attention (TOVA) at each interval. Results: Although both the boys and girls exhibited a significant decrease in the ADHD symptoms observed by parents and clinicians, the girls improved more than the boys did. Based on the teacher reports, neither the boys nor the girls exhibited significant decreases in ADHD symptoms. The symptoms rated by teachers were more severe in the boys than in the girls throughout the first 12 months; however, the gender difference lessened after 12 months. Based on the TOVA assessment, a composite score (containing response time, response time variability, and ADHD score obtained using the TOVA) did not indicate differences between genders. However, another composite score (containing omission errors, commission errors, and response sensitivity) suggested significant improvement only in the boys. Conclusions: The results suggested that according to a longitudinal follow-up, behavioral and neuropsychological changes among patients with ADHD might differ between genders. Gathering multidimensional information from patients with ADHD is essential in determining how gender modifies the functional outcome of ADHD.