Objective: Objectives of this study is to explore the neural correlates of Primary Writing Tremor (PWT) by analysing the resting state functional brain connectivity of patients with PWT and comparing the same with that of healthy controls.

Background: Primary writing tremor (PWT) is a rare task-specific tremor, which occurs only while writing or while adopting the hand in the writing position. The understanding of the neurobiology of PWT has remained controversial, as it is not clear whether PWT is a variant of essential tremor (ET) or a type of focal dystonia or a distinct disorder. This study aims is to explore small world functional brain connectivity in patients with PWT using graph theory based analysis.

Methods: This prospective case-control study included 10 patients with PWT and 10 healthy controls. All subjects underwent MRI in a 3-Tesla scanner.  Several parameters of small world functional connectivity were compared between patients and controls by using graph theory based analysis

Results: There were no significant differences in age (51.7±8.6 years vs 50.6±11.9 years), gender distribution (all were men) and MMSE scores between patients and controls. The mean duration of tremor was 3.5 ± 1.9 years. Graph theory based analysis revealed significant changes in the global as well as local parameters in patients with PWT.  The global metrics revealed significantly lower clustering coefficient (γ) and higher normalized path length (λ) in PWT compared to healthy controls. This suggests a significantly disrupted small-wordness (σ) in patients with PWT compared to controls [Figure-1]. Upon comparison of the graph metrics across a set of nodes, we observed the clustering coefficient to significantly low in several brain regions such as left and right medial cerebellum, right dorsolateral prefrontal cortex and left posterior parietal cortex.

Conclusions: Patients with PWT have significantly altered small-world brain connectivity in left and right medial cerebellum, right dorsolateral prefrontal cortex and left posterior parietal cortex. Similar to ET, alterations in cerebellar connectivity are perhaps crucial in pathogenesis of PWT.  Future studies involving larger sample size are warranted to further understand the neurobiology of this rare complex tremor disorder.

References: 1) Bain et al, Primary Writing Tremor; Brain 1995, 1461-1472

2) Berg et al, Cerebral activation pattern in primary writing tremor; JNNP, 2003, 780-786

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MDS Abstracts - https://www.mdsabstracts.org/abstract/altered-brain-network-measures-in-patients-with-primary-writing-tremor/