The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee.

Cervical dystonia is characterized by involuntary, abnormal movements and postures of the head and neck. Current views on its pathophysiology, such as faulty sensorimotor integration and impaired motor planning, are largely based on studies of focal hand dystonia. Using resting state fMRI, we explored whether cervical dystonia patients have altered functional brain connectivity compared to healthy controls, by investigating 10 resting state networks. Scans were repeated immediately before and some weeks after botulinum toxin injections to see whether connectivity abnormalities were restored. We here show that cervical dystonia patients have reduced connectivity in selected regions of the prefrontal cortex, premotor cortex and superior parietal lobule within a distributed network that comprises the premotor cortex, supplementary motor area, primary sensorimotor cortex, and secondary somatosensory cortex (sensorimotor network). With regard to a network originating from the occipital cortex (primary visual network), selected regions in the prefrontal and premotor cortex, superior parietal lobule, and middle temporal gyrus areas have reduced connectivity. In selected regions of the prefrontal, premotor, primary motor and early visual cortex increased connectivity was found within a network that comprises the prefrontal cortex including the anterior cingulate cortex and parietal cortex (executive control network). Botulinum toxin treatment resulted in a partial restoration of connectivity abnormalities in the sensorimotor and primary visual network. These findings demonstrate the involvement of multiple neural networks in cervical dystonia. The reduced connectivity within the sensorimotor and primary visual networks may provide the neural substrate to expect defective motor planning and disturbed spatial cognition. Increased connectivity within the executive control network suggests excessive attentional control and while this may be a primary trait, perhaps contributing to abnormal motor control, this may alternatively serve a compensatory function in order to reduce the consequences of the motor planning defect inflicted by the other network abnormalities.

/pdf/task-free-functional-mri-in-cervical-dystonia-reveals-multi-2id7pvgfej.pdf

Task-Free Functional MRI in Cervical Dystonia Reveals Multi-Network Changes That Partially Normalize with Botulinum Toxin

To the Editor:

We agree with Duuper et al.,1 that STN stimulation may modulate cortical excitability.2 However, the study by Duuper et al.1 raises several concerns related to methodology, results, and discussion.

Regarding the methodology, information on the age of the control group is not provided—age, however, is a crucial factor for motor evoked potentials. For a valid comparison the age group of the controls should be matched with the age of the patients. Besides, the reproducibility of the total voltage time integral may be questionable, considering the intertrial variability (see figure 1 in their article) and considering that only a few trials were averaged (possibly preselected from more trials by an unblinded observer). Movement of coil position and angle against the individual’s vertex may also have increased data variability. Moreover, patients with predominantly akinetic-rigid PD are not able to cooperate as well as controls in silent period (SP) studies requiring maintenance of a constant muscle tone.3 Consequently, …

Effects of subthalamic nucleus (STN) stimulation on motor cortex excitability

Neck muscle vibration is known to influence body orientation and posture during locomotion and stance in normal subjects. To verify the hypothesis that neck proprioceptive input can be misinterpreted in patients with cervical dystonia (CD), lateral continuous vibration was applied to the sternocleidomastoid muscle during both stepping-in-place and quiet stance, with eyes closed. The orienting responses of CD patients were compared with those of normal subjects. Vibration effects on body orientation during stepping and stance were apparently different from normal, since no effects were seen when all patients' data collapsed were analysed. However, while some patients did not respond to vibratory stimuli regardless of the vibrated side, others had a 'good' side, the stimulation of which produced effects on body orientation similar to those observed in normal subjects. Homogeneous groups within the patient population were identified, based on the vibration-induced responses under stepping conditions. The different orienting or postural responses observed in CD patients were correlated with disease-related features such as spontaneous head position, maximum range of voluntary head yaw, presence or absence of a botulinum toxin treatment and disease duration. Our data suggest that, in CD patients, the reference system used in the control of body orientation in space is either refractory to the lateralized proprioceptive neck input or modified such that the input from both sides produces an orientation shift in the same sense. This would depend on the pathogenesis of the disease or on an adaptive process connected to the head abnormal posture. It seems that this refractoriness spreads to both sides of the neck with the advancement of the disease, thereby possibly entraining a progressive shift from a reference system based on the head to a more reliable egocentric reference.

Neck proprioception and spatial orientation in cervical dystonia.

Patients with focal dystonia exhibit proprioception abnormalities that can lead to kinematic deficits. Proprioceptive abnormalities are present in both symptomatic and asymptomatic body parts of dystonic patients. To ascertain whether in patients with idiopathic cervical dystonia (CD) movements performed with nondystonic segments display kinematic abnormalities, we studied trajectory formation of out and back arm reaching movements in 10 patients with CD (before and 3 weeks after treatment with Botulinum toxin) and in 10 age-matched controls. Before treatment, patients with CD showed significant trajectory abnormalities when compared with normal controls. Patients' trajectories were more curved with asymmetrical temporal velocity profiles as well as increased hand path areas, and had longer reversal lags between the out and back segments. Treatment with botulinum toxin improved all the kinematic parameters. These results suggest that in patients with CD, movements performed with nondystonic segments are abnormal. The kinematic abnormalities are likely to derive from long-standing defective integration of the proprioceptive input, which, in turn, causes general changes in the internal models of limb dynamics. It is plausible that treatment with botulinum toxin partially restores proprioceptive processing and thus, such internal models.

Cervical dystonia affects aimed movements of nondystonic segments.

The authors studied the effects of sensorimotor integration (corticocortical inhibition and facilitation during muscle vibration [MV]) in dystonic patients. Eleven patients with cervical dystonia and 11 age-matched healthy control subjects were enrolled in the study. They were examined using transcranial magnetic stimulation (TMS) and tonic proprioceptive input (MV). Paired-pulse transcranial magnetic stimulation was done at interstimulus intervals of 3 msec (intracortical inhibition) and 13 msec, the intensity of the conditioning stimulus was 70% of the motor threshold, and the test stimulus was 120%. Motor evoked potentials were recorded from the vibrated extensor carpi radialis muscle and its antagonist, the flexor carpi radialis. Duration of MV trains (80 Hz; amplitude, 0.5 mm) was 4 seconds. The authors found differences between patients and healthy control subjects during MV only. Intracortical inhibition was pronounced significantly only in control subjects, whereas intracortical facilitation was significant in patients only (P < 0.05). Furthermore, the significant reduction of motor evoked potentials at 13-msec interstimulus intervals, which can be found in healthy subjects frequently, was observed in one dystonia patient only. The results of the current study suggest that sensorimotor integration is impaired in cervical dystonia, probably by an altered control of proprioceptive (vibratory) input.

Impaired sensorimotor integration in cervical dystonia: a study using transcranial magnetic stimulation and muscle vibration.

Introduction: Methods: Results: Discussion: Einleitung: Methodik: Ergebnisse: Diskussion:

Die transkranielle magnetische Doppelstimulation zur Beurteilung kortikokortikaler Inhibition und Fazilitierung

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Impaired sensorimotor integration in cervical dystonia: a study using transcranial magnetic stimulation and muscle vibration.

Die transkranielle magnetische Doppelstimulation zur Beurteilung kortikokortikaler Inhibition und Fazilitierung