Reduced Short Interval Cortical Inhibition Correlates with Atomoxetine Response in Children with ADHD

Clinical trials in children with Attention Deficit Hyperactivity Disorder (ADHD) show variability in behavioral responses to the selective norepinephrine reuptake inhibitor atomoxetine (ATX). The objective of this study was to determine whether Transcranial Magnetic Stimulation (TMS)-evoked Short Interval Cortical Inhibition (SICI) might be a biomarker predicting, or correlating with, clinical ATX response. At baseline and after 4 weeks of ATX treatment in 7–12 year old children with ADHD, TMS-SICI was measured, blinded to clinical improvement. Primary analysis was by multivariate ANCOVA. Baseline SICI did not predict clinical responses. However, paradoxically, after 4 weeks of ATX, mean SICI was reduced 31.9% in responders and increased 6.1% in non-responders (ANCOVA t 41 =2.88; p = .0063). Percent reductions in SICI correlated with reductions in ADHD-Rating Scale (ADHDRS) (r = .50; p = .0005). In children ages 7–12 years with ADHD treated with ATX, improvements in clinical symptoms are correlated with reductions in motor cortex SICI.