Objective: The primary objective of this study was to identify the brain regions contributing to dysfluent writing behavior in a subtype of dystonia called writer’s cramp (WC), in which dystonic movements occurred during right-hand writing.

Background: Dystonia is a disabling brain disorder with no disease-modifying treatments and limited efficacy from symptomatic therapies. Developing effective clinical therapies is contingent on a better understanding of the relationship between brain abnormalities and behavioral measures of dystonia.

Method: 16 healthy volunteers (HV) and 18 WC completed a behavior writing assay and task-based fMRI. The writing assay consisted of copying a single sentence ten times in kinematic writing software to provide a behavioral measure of writing dysfluency called peak accelerations. During fMRI, subjects performed writing alternated by rest in a block design.

To analyze brain-behavior relationships, functional connectivity analysis was performed using brain regions known to play a role in the dystonia motor network. These functional connectivities were then correlated within subject with the behavior of peak accelerations and analyzed for group differences using generalized linear modeling. Lastly, a mixed effects model was performed to identify the brain regions primarily contributing to the group differences in brain-behavior associations.

Results: WC subjects showed greater dysfluent writing behavior compared to HV (difference 129 counts, p<0.0001). The greater dysfluent behavior correlated with reduced functional connectivity between left putamen-right cerebellum (R= -0.70, p= 0.009) in right-hand WC, but not HV (R= -0.0008, p= 0.997) and this group difference was statistically significant (difference: 539, p= 0.006). Brain activity analysis also showed reduced BOLD activity in the left putamen (0.24, p= 0.018) but not in the right cerebellum (-0.001, p= 0.992) in WC compared to HV.

Conclusion: Dysfluent writing behavior in WC subjects is associated with reduced putamen-cerebellum connectivity which is largely due to reduced putamen BOLD activity in WC subjects. Future clinical therapies that increase putamen BOLD activity may allow for improvement in dystonic behavior in WC subjects.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dysfluent-writing-behavior-associates-with-reduced-striatal-cerebellar-connectivity-in-writers-cramp-dystonia/