Multiple changes of functional connectivity between sensorimotor areas in focal hand dystonia

Background: Task-specific focal hand dystonia impairs the control of arm muscles during fine motor skills such as writing (writer's cramp (WC)). Functional imaging found abnormal task-related activation of sensorimotor areas in this disorder, but little is known on their functional connectivity (FC). Methods: Resting-state fMRI and regions of interest (ROI)-voxel cross-correlation analyses were used for systematically analysing the FC between multiple ROIs within the cerebello-basal ganglia-thalamocortical network in 15 patients with right-sided WC and 15 healthy volunteers. Results: Patients with WC showed a lower positive FC of several seed ROIs (left lateral premotor cortex, left thalamus, left/right pallidum) to the symptomatic left primary sensorimotor cortex compared with controls. The FC of the left primary motor cortex to prefrontal areas, pre- supplementary motor area and right somatosensory cortex was reduced and correlated with disease severity. Several cerebellar seed ROIs (right dentate nucleus, right crus I and bilateral crus II) revealed a stronger negative FC to primary and secondary sensorimotor areas. Conclusions: An increase of negative cerebello-cortical FC at rest is in line with the hypothesis of a pathogenetic role of the cerebellum in dystonia. The deficit of positive subcortico-cortical FC indicates more generalised changes within the basal ganglia-thalamocortical motor loops beyond primary sensorimotor areas in WC. As patients with WC are asymptomatic during rest, these functional network changes could reflect an underlying abnormality or compensatory neuroplastic changes of network architecture in this disorder.