What causes involuntary tics in Tourette syndrome (TS)?

Updated: May 30, 2019
  • Author: William C Robertson, Jr, MD; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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Studies using back-averaging techniques have shown that the premovement potential in TS is often absent prior to the appearance of an involuntary movement. This observation supports that the tics are involuntary. [80] Event-related potentials that indicate motor preparation, inhibition of prepotent motor responses, or unexpected events have been variably abnormal in TS patients. [81, 82, 81, 83]

Several laboratories have used short-interval transcranial magnetic stimulation (TMS) to investigate cortical inhibition in TS. In 1997, Ziemann et al showed abnormal cortical inhibition in tic patients. [84] However, in 2001 Moll et al suggested that this was not specific to a TS diagnosis but was accounted for by a comorbid diagnosis of ADHD. [85] Findings from a follow-up study in 2003 suggested that an OCD diagnosis might also account for the original results.

In a 2004 study using transcranial magnetic stimulation, Gilbert et al found that current (recent) severity of tics and hyperactivity in a group of TS subjects was associated significantly and independently with short-interval cortical inhibition. [86] ADHD symptoms, specifically hyperactivity, showed the closest correlation. Repeat studies in the same children replicated these findings and demonstrated their temporal stability. [87] The results have been independently replicated. [88]

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