Cervical dystonia is a non-degenerative movement disorder characterised by dysfunction of both motor and sensory cortico-basal ganglia networks. Deep brain stimulation targeted to the internal pallidum (GPi) is an established treatment, but its specific mechanisms remain elusive, and response to therapy is highly variable. Modulation of key dysfunctional networks via axonal connections is likely important. Fifteen patients underwent pre-operative diffusion-MRI acquisitions and then progressed to bilateral DBS targeting the posterior GPi. Severity of disease was assessed pre-operatively and later at follow-up. Scans were used to generate tractography-derived connectivity estimates between the bilateral regions of stimulation and relevant structures. Connectivity to the putamen correlated with clinical improvement, and a series of cortical connectivity-based putaminal parcellations identified the primary motor (M1) putamen as the key node (r = 0.70, p = 0.004). A regression model with this connectivity and electrode coordinates explained 68% of variance in outcomes (r = 0.83, p = 0.001), with both as significant explanatory variables. We conclude that modulation of the M1 putamen-posterior GPi limb of the cortico-basal ganglia loop is characteristic of successful DBS treatment of cervical dystonia. Pre-operative diffusion imaging contains additional information that predicts outcomes, implying utility for patient selection and/or individualised targeting.
globus pallidus interna, motor cortex, putamen, spasmodic torticollis, tractography