TMS-evoked potentials provide novel neurophysiological features of Tourette syndrome

Gilles de la Tourette syndrome (TS) is a neuropsychiatric disorder associated with abnormal activation of the cortico-striatal-thalamo-cortical circuits and dopaminergic system. We sought to examine changes in neurotransmission relating to cortical excitation/inhibition of TS by measuring TMS-evoked potentials (TEPs) of selected networks.

Thirty-three adult TS patients and 18 healthy controls underwent evaluation of symptom severity using the YGTSS (tics), PUTS (premonitory urge), Y-BOCS (OCD), CAARS (ADHD), BDI (depression), and BAI (anxiety). TMS-EEG was performed to measure TEPs obtained from the primary motor cortex (M1), dorsolateral prefrontal cortex (DLPFC), and primary visual cortex (V1).

TEP analysis revealed a delayed P180 latency in M1 for TS patients compared to controls (p = 0.006). Lower early amplitude of TEP in response to stimulation of DLPFC (50-70 ms), and delayed DLPFC P180 latency were associated with higher tic severity (p = 0.001 and p = 0.003, respectively). M1 early amplitude (50-70 ms) also effectively differentiated TS with mild-moderate from severe tics (p = 0.003). Significant correlation was found between TEP V1 early amplitude (15-45 ms) and severity of TS anxiety.

Distinct TEP patterns registered in response to DLPFC, M1, and V1 stimulation may shed light on the underlying pathophysiology of TS and are associated with tic severity and comorbidities.