Top-down alteration of functional connectivity within the sensorimotor network in focal dystonia

Altered sensory system activity and connectivity patterns in adductor spasmodic dysphonia

Adductor-type spasmodic dysphonia (ADSD) manifests in effortful speech temporarily relievable by botulinum neurotoxin type A (BoNT-A). Previously, abnormal structure, phonation-related and resting-state sensorimotor abnormalities as well as peripheral tactile thresholds in ADSD were described. This study aimed at assessing abnormal central tactile processing patterns, their spatial relation with dysfunctional resting-state connectivity, and their BoNT-A responsiveness. Functional MRI in 14/12 ADSD patients before/under BoNT-A effect and 15 controls was performed (i) during automatized tactile stimulus application to face/hand, and (ii) at rest. Between-group differential stimulation-induced activation and resting-state connectivity (regional homogeneity, connectivity strength within selected sensory(motor) networks), as well as within-patient BoNT-A effects on these differences were investigated. Contralateral-to-stimulation overactivity in ADSD before BoNT-A involved primary and secondary somatosensory representations, along with abnormalities in higher-order parietal, insular, temporal or premotor cortices. Dysphonic impairment in ADSD positively associated with left-hemispheric temporal activity. Connectivity was increased within right premotor (sensorimotor network), left primary auditory cortex (auditory network), and regionally reduced at the temporoparietal junction. Activation/connectivity before/after BoNT-A within-patients did not significantly differ. Abnormal ADSD central somatosensory processing supports its significance as common pathophysiologic focal dystonia trait. Abnormal temporal cortex tactile processing and resting-state connectivity might hint at abnormal cross-modal sensory interactions.

Normal Temporal Discrimination in Musician's Dystonia Is Linked to Aberrant Sensorimotor Processing

OBJECTIVES

Alterations in sensory discrimination are a prominent nonmotor feature of dystonia. Abnormal temporal discrimination in focal dystonia is considered to represent its mediational endophenotype, albeit unclear pathophysiological correlates. We examined the associations between the visual temporal discrimination threshold (TDT) and brain activity in patients with musician's dystonia, nonmusician's dystonia, and healthy controls.

METHODS

A total of 42 patients and 41 healthy controls participated in the study. Between-group differences in TDT z scores were computed using inferential statistics. Statistical associations of TDT z scores with clinical characteristics of dystonia and resting-state functional brain activity were examined using nonparametric rank correlations.

RESULTS

The TDT z scores of healthy controls were significantly different from those of patients with nonmusician's dystonia, but not of patients with musician's dystonia. Healthy controls showed a significant relationship between normal TDT levels and activity in the inferior parietal cortex. This relationship was lost in all patients. Instead, TDT z scores in musician's dystonia established additional correlations with activity in premotor, primary somatosensory, ventral extrastriate cortices, inferior occipital gyrus, precuneus, and cerebellum, whereas nonmusician's dystonia showed a trending correlation in the lingual gyrus extending to the cerebellar vermis. There were no significant relationships between TDT z scores and dystonia onset, duration, or severity.

CONCLUSIONS

TDT assessment as an endophenotypic marker may only be relevant to nonmusician forms of dystonia because of the lack of apparent alterations in musician's dystonia. Compensatory adaptation of neural circuitry responsible for TDT processing likely adjusted the TDT performance to the behaviorally normal levels in patients with musician's dystonia, but not nonmusician's dystonia. © 2020 International Parkinson and Movement Disorder Society.

The large-scale structural connectome of task-specific focal dystonia

The emerging view of dystonia is that of a large‐scale functional network disorder, in which the communication is disrupted between sensorimotor cortical areas, basal ganglia, thalamus, and cerebellum. The structural underpinnings of functional alterations in dystonia are, however, poorly understood. Notably, it is unclear whether structural changes form a larger‐scale dystonic network or rather remain focal to isolated brain regions, merely underlying their functional abnormalities. Using diffusion‐weighted imaging and graph theoretical analysis, we examined inter‐regional white matter connectivity of the whole‐brain structural network in two different forms of task‐specific focal dystonia, writer's cramp and laryngeal dystonia, compared to healthy individuals. We show that, in addition to profoundly altered functional network in focal dystonia, its structural connectome is characterized by large‐scale aberrations due to abnormal transfer of prefrontal and parietal nodes between neural communities and the reorganization of normal hub architecture, commonly involving the insula and superior frontal gyrus in patients compared to controls. Other prominent common changes involved the basal ganglia, parietal and cingulate cortical regions, whereas premotor and occipital abnormalities distinctly characterized the two forms of dystonia. We propose a revised pathophysiological model of focal dystonia as a disorder of both functional and structural connectomes, where dystonia form‐specific abnormalities underlie the divergent mechanisms in the development of distinct clinical symptomatology. These findings may guide the development of novel therapeutic strategies directed at targeted neuromodulation of pathophysiological brain regions for the restoration of their structural and functional connectivity.

Sensitivity and pain in focal dystonia of the hand

INTRODUCTION

A growing body of evidence highlights the importance of understanding both the sensory and the motor pathophysiology of focal dystonia in order to improve its treatment. This study aims to evaluate somatosensory afferences in patients with focal or segmental dystonia affecting the upper limbs, to analyse whether the dominant limb is more frequently affected, to analyse pain tolerance, and to examine the potential association with pain perception in patients with hand dystonia.

METHODS

We recruited 24 participants: 12 patients with focal hand dystonia and 12 individuals without dystonia. All participants were evaluated with a digital algometer (Somedic SenseLab AB®, Farsta, Sweden), a Semmes-Weinstein monofilament test, and the visual analogue scale for pain.

RESULTS

According to our data, patients showed greater impairment in surface sensitivity than controls, both in the dominant and the non-dominant hands, as well as greater presence of pain (P>.001). Furthermore, the dystonia group showed a negative correlation between perceived pain and pressure pain tolerance threshold (rho=-0.83; P<.001).

CONCLUSIONS

Patients with focal hand dystonia presented alterations in sensitivity and more severe perceived pain than individuals without dystonia. Future studies with larger samples should aim to analyse the clinical implications and everyday impact of both objective and subjective pain.