Article

Motor cortex excitability and comorbidity in Gilles de la Tourette syndrome

Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, London, UK.
Journal of neurology, neurosurgery, and psychiatry (Impact Factor: 5.58). 11/2008; 80(1):29-34. DOI: 10.1136/jnnp.2008.149484
Source: PubMed

ABSTRACT Gilles de la Tourette syndrome (GTS) is often complicated by comorbid attention-deficit/hyperactivity disorder (ADHD) or obsessive-compulsive disorder (OCD). This study examines whether motor cortex excitability differs between uncomplicated GTS patients and those complicated by ADHD or OCD.
Motor thresholds, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), and short latency afferent inhibition (SAI) were measured using transcranial magnetic stimulation (TMS) in 29 untreated GTS patients (18 uncomplicated, six with comorbid ADHD, five with comorbid OCD) and 24 healthy subjects. Tic severity was rated with standard clinical scales.
Patients had slightly higher resting (RMT) and active motor thresholds (AMT). The threshold of SICI and ICF expressed as a percentage of each individual's AMT was similar in controls and GTS patients. Above threshold, GTS patients had less SICI and more ICF. SICI was similar in all subgroups, but ICF differed significantly between them. Patients with GTS+ADHD had more ICF than controls, uncomplicated GTS patients or GTS+OCD patients; ICF was similar in these other groups. GTS patients as a whole had reduced SAI. Uncomplicated GTS patients or GTS+ADHD patients had less SAI than controls or GTS+OCD patients.
GTS with ADHD comorbidity is associated with more extensive changes in the excitability of motor cortex circuits than uncomplicated GTS or GTS+OCD. The extent to which various different neuronal circuits are affected may be relevant for the phenotype of Tourette spectrum disorders.

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    • "For example , some electrophysiological studies (using transcranial magnetic stimulation) have found reduced cortical inhibition in the primary motor cortex in TS/CTD (Ziemann et al., 1997; Gilbert et al., 2004), suggesting altered motor inhibition. However, other studies have shown that differences in cortical excitability may be more related to comorbid attention deficit hyperactivity disorder (ADHD) symptoms than to tics (Gilbert et al., 2005; Orth and Rothwell, 2009). Similarly, although behavioral studies in children and adults with TS/CTD have demonstrated impairments in response inhibition, selective attention, and cognitive flexibility (Bornstein et al., 1991; Channon et al., 2003, 2009; Watkins et al., 2005), some have argued that these impairments are driven by comorbid conditions, including ADHD and obsessive-compulsive disorder (OCD) (Ozonoff et al., 1998; Denckla, 2006). "
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    • "These studies show considerable consistency, and demonstrate the following. First, resting motor threshold (RMT) and active motor threshold (AMT) do not typically differ between individuals with TS and controls (Heise et al., 2010; Moll et al., 1999, 2001; Orth et al., 2005, 2008; Ziemann et al., 1997; but see Orth & Rothwell, 2009). Second, the duration of the cortical silent period (CSP) induced by TMS to motor cortex, and the magnitude of the short-interval intra-cortical inhibition (SICI) that is observed, are both significantly reduced in individuals with TS relative to matched controls (e.g., Gilbert et al., 2004; Moll et al., 1999, 2001; Orth et al., 2008; Ziemann et al., 1997). "
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