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

Abstract

AimTo 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.

Interpreting and analysing measures of motor inhibition in Tourette research and beyond

“…Several small‐scale studies in adults and adolescents have reported a reduction in SICI; 3 however, this has been less well explored in younger children. Batschelett et al 4 collected several TMS measures (including SICI) from a sample of 30 Tourette syndrome and 30 control participants aged 8 to 12 years. Interestingly, after accounting for ADHD – 15 of the 30 with Tourette syndrome also had ADHD – SICI was not found to be significantly reduced in comparison to controls.…”