Corticospinal system excitability at rest is associated with tic severity in tourette syndrome.
BACKGROUND
Several measures of motor cortex excitability are abnormal in Gilles de la Tourette syndrome (GTS). However, it is not clear whether these represent abnormalities of specific pathways or reflect a more widespread reduction of motor cortex excitability. Their significance for the clinical phenotype is also unknown.


METHODS
We measured motor thresholds, input-output (I/O) curves, short interval intracortical inhibition (SICI), and cortical silent period (SP) with transcranial magnetic stimulation in 20 untreated GTS patients (12 uncomplicated, 4 with comorbid attention-deficit/hyperactivity disorder, 4 with comorbid obsessive-compulsive disorder) and 24 healthy subjects. Tics were rated with standard clinical scales and detailed video analysis.


RESULTS
Thresholds did not differ between groups. At rest, patients had shallower I/O curve slopes, despite their tics, and reduced SICI. Slopes were equal during voluntary muscle activation, as was the SP duration. Resting I/O slopes correlated, in uncomplicated GTS patients, most strongly to ratings of complex tics, hand and finger tics, and vocal tics, with shallower slopes predicting fewer tics. In complicated patients, good correlations were seen with neck/shoulder tics and vocal tics.


CONCLUSIONS
Corticospinal excitability in patients at rest is reduced. We suggest this is an adaptive response that may reduce release of unwanted movements.
Orth
Michael
M
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, London, United Kingdom. m.orth@uke.uni-hamburg.de
Münchau
Alexander
A
Rothwell
John C
JC
D000328:Adult; D000704:Analysis of Variance; D004056:Differential Threshold; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009433:Neural Inhibition / Q000502:physiology; D011712:Pyramidal Tracts / Q000503:physiopathology*; D012044:Regression Analysis; D012146:Rest / Q000502:physiology*; D012720:Severity of Illness Index; D020323:Tics / Q000209:etiology*; D005879:Tourette Syndrome / Q000150:complications* / Q000473:pathology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods