Motor cortex excitability in 29 untreated adult Gilles de la Tourette syndrome (TS) patients was measured using transcranial magnetic stimulation in a study at the Institute of Neurology, London, UK, and University of Ulm, Germany. A group of comorbid TS and ADHD patients showed abnormalities of measures of motor cortex excitability, patients with uncomplicated TS had abnormal results in all measures except intracortical facilitation, and patients with comorbid TS and OCD had abnormal short-interval intracortical inhibition and thresholds but normal levels of intracortical facilitation and short latency afferent inhibition. TS with ADHD comorbidity is associated with more extensive changes in the excitability of motor cortex circuits than uncomplicated TS or TS+OCD. The phenotype of TS may be related to the extent of involvement of different neuronal circuits. 
COMMENT. Transcranial magnetic stimulation (TMS) is a non-invasive method of measurement of motor cortex excitability while awake. TMS studies have demonstrated alterations of motor cortex excitability in patients with TS, uncomplicated and in those with ADHD or OCD comorbidity. Involvement of different neuronal circuits may be correlated with various subtypes of TS, alone or comorbid with ADHD or OCD.