Effects of Long-Acting Methylphenidate in Adults with Attention Deficit Hyperactivity Disorder: A Study with Paired-Pulse Transcranial Magnetic Stimulation

Abstract

Background: Methylphenidate improves attention deficits, hyperactivity and impulsivity in attention deficit hyperactivity disorder (ADHD). Recent investigations into motor cortex excitability with paired-pulse transcranial magnetic stimulation (ppTMS) technique have shown inhibition deficits in ADHD which correlate with clinical symptomatology. Therefore, we investigated the neurophysiological effects of long-acting methylphenidate (LA-Mph) with the ppTMS technique in adult patients with ADHD. Methods: Thirteen right-handed adult ADHD patients who were first diagnosed with ADHD were included in this ppTMS study. Measurements took place before and during treatment with LA-Mph (30–54 mg/day). Statistical analyses were performed to investigate treatment effects and correlations with clinical symptomatology. Results: LA-Mph significantly decreased the relative short intracortical motor inhibition (SICI) magnetically evoked potential (MEP) amplitude at 3-ms interstimulus interval (conditioned/unconditioned MEP amplitude: 0.83 ± 0.76 drug-free vs. 0.29 ± 0.19 with LA-Mph; p = 0.020). The relative intracortical facilitation MEP amplitude at 11 ms interstimulus interval (conditioned/unconditioned MEP amplitude: 1.51 ± 0.92 drug-free vs. 1.79 ± 0.95 with LA-Mph) was not significantly increased. The reduced relative SICI MEP amplitude with LA-Mph correlated significantly with the improvement of the psychopathological ADHD self-rating total scores (p = 0.046). Conclusion: These results show that in adult patients with ADHD, LA-Mph significantly improves motor disinhibition and might have differential stabilizing effects on motor hyperexcitability.