Biomarkers of tic severity in children with Tourette syndrome: Motor cortex inhibition measured with transcranial magnetic stimulation

Abstract

AbstractAimTo compare transcranial magnetic stimulation (TMS)‐derived measures of primary motor cortex (M1) physiology between children with and without Tourette syndrome, and to dimensionally analyze TMS measures with Tourette syndrome‐related symptom severity.MethodWe used a cross‐sectional experimental design. Sixty 8‐ to 12‐year‐old children participated (30 with Tourette syndrome: three females, mean age 10 years 10 months, standard deviation [SD] 1 year 3 months; 30 typically developing children: seven females, mean age 10 years 7 months, SD 1 year 3 months). In the group with Tourette syndrome, 15 (one female, mean age 10 years 11 months, SD 1 year 3 months) had comorbid attention‐deficit/hyperactivity disorder (ADHD), rated with the Conners, Third Edition and the parent‐reported ADHD rating scales. Tic severity was rated with the Yale Global Tic Severity Scale and urge severity with the Individualized Premonitory Urge for Tics Scale. M1 short‐interval cortical inhibition (SICI) and intracortical facilitation were compared between diagnostic groups and, within the group with Tourette syndrome, correlated with symptom severity using linear mixed‐effects models for repeated measures.ResultsAccounting for ADHD, we found no difference in SICI or intracortical facilitation in those with Tourette syndrome versus typically developing children (p > 0.1). In the group with Tourette syndrome, reduced M1 SICI predicted greater total (p = 0.012) and global (p = 0.002) tic severity. There were no associations with urge severity (p > 0.5).InterpretationReduced M1 SICI is robustly associated with increased tic, but not urge, severity.What this paper adds Increased tic severity is associated with reduced motor cortex short‐interval cortical inhibition (SICI). Children with Tourette syndrome with increased urge severity also show increased tic severity. However, reduced motor cortex SICI is associated with tic, but not urge, severity.