Abstract
Dystonia, a debilitating neurological movement disorder, is characterized by involuntary muscle contractions and develops from a complex pathophysiology. Graph theoretical analysis approaches have been employed to investigate functional network changes in patients with different forms of dystonia. In this study, we aimed to characterize the abnormal brain connectivity underlying writer's cramp, a focal hand dystonia. To this end, we examined functional magnetic resonance scans of 20 writer's cramp patients (11 females/nine males) and 26 healthy controls (10 females/16 males) performing a sequential finger tapping task with their non-dominant (and for patients non-dystonic) hand. Functional connectivity matrices were used to determine group averaged brain networks. Our data suggest that in their neuronal network writer's cramp patients recruited fewer regions that were functionally more segregated. However, this did not impair the network's efficiency for information transfer. A hub analysis revealed alterations in communication patterns of the primary motor cortex, the thalamus and the cerebellum. As we did not observe any differences in motor outcome between groups, we assume that these network changes constitute compensatory rerouting within the patient network. In a secondary analysis, we compared patients with simple writer's cramp (only affecting the hand while writing) and those with complex writer's cramp (affecting the hand also during other fine motor tasks). We found abnormal cerebellar connectivity in the simple writer's cramp group, which was less prominent in complex writer's cramp. Our preliminary findings suggest that longitudinal research concerning cerebellar connectivity during WC progression could provide insight on early compensatory mechanisms in WC.
Highlights
Dystonia is the third most common type of movement disorder [1]
For writer’s cramp (WC) patients, this was true for 131 nodes
We showed that WC patients exhibited a reduced number of regions contributing to the network
Summary
Dystonia is the third most common type of movement disorder [1]. It includes heterogeneous symptoms characterized by involuntary muscle contractions resulting in abnormal movement patterns [2]. In the case of writer’s cramp (WC), dystonic symptoms affect the dominant hand during writing or, in a more complex form of the disease, during additional fine motor tasks [3]. While the different forms of dystonia have been clinically well-characterized, the cause of WC remains unclear. Several studies demonstrated a loss of surround inhibition in the primary motor cortex and abnormal basal ganglia activity [4,5,6,7]. A sensory disorder has been postulated, including maladaptive cortical plasticity with dedifferentiation of somatosensory representations [8, 9], abnormal temporal discrimination [10], impaired cortical somatosensory processing and abnormal sensorimotor integration [11, 12]
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