Reliability of short interval cortical inhibition in children with attention deficit hyperactivity disorder

Abstract

Objective: Utility of biomarkers depends on test-retest consistency. Reduced Short Interval Cortical Inhibition (SICI) has emerged as a consistent finding in children with Attention Deficit Hyperactivity Disorder (ADHD); however, test-retest has not been established for children with ADHD. This is particularly crucial given that Transcranial Magnetic Stimulation (TMS) motor evoked potential (MEP)-based measures have high intra-subject variability and susceptibility to state-effects on motor cortex excitability. Addressing this, the objective of this study was to estimate test-retest reliability of paired-pulse SICI and of Intracortical Facilitation (ICF) in children, including those with ADHD and typically developing (TD) controls.

Methods: Sixty-four 8-to-12-year-old children (28 female; 35 ADHD; 29 TD) were recruited at two sites and SICI and ICF measured across two visits separated by 21 days. Intraclass correlations (ICCs) were calculated.

Results: Good reliability for SICI (ICC > 0.75), but only moderate for ICF (ICC > 0.50), was found among ADHD children, after accounting for test-pulse MEP amplitudes (>0.25 mV) and outliers.

Conclusions: These findings support the potential for SICI as a biomarker of ADHD in school-aged children.

Significance: This research addresses a critical gap in clinical neurophysiology, as estimating the reliability of SICI is needed to utilize it in interventional or longitudinal studies.

Keywords: Attention deficit hyperactivity disorder; Biomarker; Children; Motor cortex; Short interval cortical inhibition; Transcranial magnetic stimulation.