Basic and Translational Neuroscience of Childhood-Onset Dystonia: A Control-Theory Perspective

Globus pallidus internus activity increases during voluntary movement in children with dystonia

The rate model of basal ganglia function predicts that muscle activity in dystonia is due to disinhibition of thalamus resulting from decreased inhibitory input from pallidum. We seek to test this hypothesis in children with dyskinetic cerebral palsy undergoing evaluation for deep brain stimulation (DBS) to analyze movement-related activity in different brain regions. The results revealed prominent beta-band frequency peaks in the globus pallidus interna (GPi), ventral oralis anterior/posterior (VoaVop) subnuclei of the thalamus, and subthalamic nucleus (STN) during movement but not at rest. Connectivity analysis indicated stronger coupling between STN-VoaVop and STN-GPi compared to GPi-STN. These findings contradict the hypothesis of decreased thalamic inhibition in dystonia, suggesting that abnormal patterns of inhibition and disinhibition, rather than reduced GPi activity, contribute to the disorder. Additionally, the study implies that correcting abnormalities in GPi function may explain the effectiveness of DBS targeting the STN and GPi in treating dystonia.

The immediate effect of different loads does not alter muscle co-activation of the upper limb in young adults with dyskinetic cerebral palsy

BACKGROUND

There is insufficient information on muscle co-activation in the upper limbs to help healthcare providers develop treatment programs for patients with dyskinetic cerebral palsy (DCP).

RESEARCH QUESTION

Is the degree of muscle co-activation greater in adults with DCP than in healthy individuals? Does the use of different arm weights modify co-contraction in individuals with PCD?

METHODS

Fourteen healthy individuals (control group [CG]) and 14 individuals with DCP (dyskinetic group [DG]) participated in the study. The degree of muscle co-activation of the dominant limb during drinking from a mug was compared between the two groups. The task was divided into a going, adjusting, and returning phase. In the DG, an analysis was also performed on using an arm weight during the functional task. The loads corresponded to 10, 20, and 30 % of maximum isometric muscle strength measured in each participant.

RESULTS

In comparing the two groups, the DG exhibited a greater muscle co-activation in the shoulder and elbow muscles during the going phase, the shoulder, elbow, and wrist during the adjusting phase; and the elbow during the returning phase. The DG also showed a greater mean index of curvature (MIC), time to perform the movement phases, and lesser mean velocity (Vm) to drinking. In analyzing the DG's arm weight, no effect on co-activation, MIC, time to perform the movement phases, and Vm to drinking were found with the loads tested (p > 0.05).

CONCLUSION

Muscle co-activation is increased in adults with DCP in comparison to healthy individuals. Moreover, arm weight during the functional activity of drinking from a mug did not alter co-activation, although an immediate effect was expected.

Dystonia assessment in children with cerebral palsy and periventricular leukomalacia

OBJECTIVE

To describe the frequency, motor phenotype, clinical patterns and functional consequences of dystonia in patients with cerebral palsy (CP) in the setting of periventricular leukomalacia.

METHODS

Retrospective analysis of a cohort of 31 patients with CP and periventricular leukomalacia. Gross Motor Function Classification System (GMFCS) and Manual Ability Classification System (MACS) were used to classify functional ability. Spasticity was rated using the Modified Ashworth Scale. Presence of dystonia was assessed by reviewing video recordings, and its severity by using the Burke-Fahn-Marsden Dystonia Rating Scale.

RESULTS

All patients showed evidence of dystonia involving upper and/or lower limbs, neck, trunk, mouth and eyes in order of frequency. In 29% of patients dystonia involved only the limbs and in 71% it was multifocal. Dystonia severity ranged from slight to severe. Severity and distribution of dystonia did not correlate with gender, age, weeks of gestation or duration of neonatal unit stay. GMFCS and MACS correlated with dystonia but not with spasticity.

CONCLUSIONS

Severity of dystonia, but not spasticity is associated with the severity of motor functional disability in CP patients with periventricular leukomalacia and demonstrates the key role of dystonia in the motor function of these patients.

High-fidelity transmission of high-frequency burst stimuli from peripheral nerve to thalamic nuclei in children with dystonia

High-frequency peripheral nerve stimulation has emerged as a noninvasive alternative to thalamic deep brain stimulation for some patients with essential tremor. It is not known whether such techniques might be effective for movement disorders in children, nor is the mechanism and transmission of the peripheral stimuli to central brain structures understood. This study was designed to investigate the fidelity of transmission from peripheral nerves to thalamic nuclei in children with dystonia undergoing deep brain stimulation surgery. The ventralis intermediate (VIM) thalamus nuclei showed a robust evoked response to peripheral high-frequency burst stimulation, with a greatest response magnitude to intra-burst frequencies between 50 and 100 Hz, and reliable but smaller responses up to 170 Hz. The earliest response occurred at 12–15 ms following stimulation onset, suggesting rapid high-fidelity transmission between peripheral nerve and thalamic nuclei. A high-bandwidth, low-latency transmission path from peripheral nerve to VIM thalamus is consistent with the importance of rapid and accurate sensory information for the control of coordination and movement via the cerebello-thalamo-cortical pathway. Our results suggest the possibility of non-invasive modulation of thalamic activity in children with dystonia, and therefore the possibility that a subset of children could have beneficial clinical response without the need for invasive deep brain stimulation.

Dystonia and dopamine: From phenomenology to pathophysiology

A line of evidence suggests that the pathophysiology of dystonia involves the striatum, whose activity is modulated among other neurotransmitters, by the dopaminergic system. However, the link between dystonia and dopamine appears complex and remains unclear. Here, we propose a physiological approach to investigate the clinical and experimental data supporting a role of the dopaminergic system in the pathophysiology of dystonic syndromes. Because dystonia is a disorder of motor routines, we first focus on the role of dopamine and striatum in procedural learning. Second, we consider the phenomenology of dystonia from every angle in order to search for features giving food for thought regarding the pathophysiology of the disorder. Then, for each dystonic phenotype, we review, when available, the experimental and imaging data supporting a connection with the dopaminergic system. Finally, we propose a putative model in which the different phenotypes could be explained by changes in the balance between the direct and indirect striato-pallidal pathways, a process critically controlled by the level of dopamine within the striatum. Search strategy and selection criteria References for this article were identified through searches in PubMed with the search terms « dystonia », « dopamine", « striatum », « basal ganglia », « imaging data », « animal model », « procedural learning », « pathophysiology », and « plasticity » from 1998 until 2018. Articles were also identified through searches of the authors' own files. Only selected papers published in English were reviewed. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.