Objective: We investigated neurophysiological mechanisms of writer’s cramp dystonia during drawing movements.

Background: Writer’s cramp is a focal task-specific dystonia characterized by involuntary muscle contractions during handwriting. Electrophysiological impairments, including altered cortical activity, have been reported in people with writer’s cramp dystonia [1], but the underlying mechanisms remain poorly understood. A comprehensive characterization of cortical and subcortical interactions during movement execution is essential to unravel the complexity of writer’s cramp dystonia and its underlying neural dynamics. We aimed to investigate the neurophysiological mechanisms associated with drawing impairments in writer’s cramp dystonia recording high-density electroencephalography (hd-EEG) during a spiral drawing task. We hypothesized that impairments in motor execution relate to altered communication within the cortico-subcortical network involved in drawing.

Method: To investigate neural activity underlying drawing impairments, we recorded hd-EEG during spiral drawing in 26 patients with writer’s cramp dystonia (10 female; Age = 49.3±4.8; WCRS = 10.4±3.2; ADDS = 60.4±8.7) and 26 age- and sex-matched (Age = 45.2±7.8) healthy controls. We identified cortical and subcortical source activity linked to movement execution applying EEG beamformer analysis. To examine the directional interactions between cortical and subcortical regions, effective connectivity was estimated using time-resolved partial directed coherence. Motor performance was assessed using multiscale entropy as a measure of complexity and irregularity underlying the drawing velocity signals [2].

Results: Both groups showed activation in the motor cortex, premotor cortex, supplementary motor area, and cerebellum during drawing. However, healthy individuals also exhibited activity in the posterior parietal cortex and thalamus, which was absent in patients with dystonia. Instead, patients displayed increased activity in the putamen. Premotor cortical source coherence correlated with clinical impairment (r = 0.88; p < 0.001), and the strength of information flow from cerebellum to premotor cortex correlated with multiscale entropy (r = 0.63; p < 0.001).

Conclusion: These findings suggest that motor dysfunction in writers cramp relates to altered activity in distinct neural pathways, underscoring the potential of EEG for diagnosis and monitoring for dystonia.

References: 1. Thirugnanasambandam, N., et al., Task-specific interhemispheric hypoconnectivity in writer’s cramp – An EEG study. Clin Neurophysiol, 2020. 131(5): p. 985-993.
2. Bange, M., et al., Deficient Interhemispheric Connectivity Underlies Movement Irregularities in Parkinson’s Disease. J Parkinsons Dis, 2022. 12(1): p. 381-395.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/drawing-impairments-linked-to-altered-cortico-subcortical-interactions-in-writers-cramp/