Objective: To investigate dystonia associated with PD in patients undergoing unilateral subthalamic nucleus (STN) DBS implantation.

Background: Dystonia is a twisting, involuntary movement that often occurs in PD, yet it is relatively neglected as a research topic versus the cardinal symptoms (tremor, rigidity, bradykinesia). Dystonia ‘off’ dopaminergic medications usually manifests initially in the foot and can be associated with pain and decreases in mobility. Although lower limb symptoms often improve with DBS, they can be more resistant to therapy compared to arm symptoms. We and others have demonstrated DBS current fractionation within the STN region can improve refractory symptoms in the lower limbs. Here we expand on this research, using novel directional leads to investigate local field potentials, and DBS efficacy as they relate to dystonia in PD.

Method: We recruited and consented eighteen consecutive PD patients who were undergoing unilateral directional STN DBS as part of routine care. We assessed dystonia preoperatively and at 2 and 4 months post-op with both the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) and Burk-Fahn Marsden Dystonia Severity Scale (BFM). Intraoperative cortical and subcortical field potentials were recorded at rest and during simple repetitive voluntary movements from both a six-contact electrocorticography strip over ipsilateral motor cortex and from the directional DBS lead in the STN region. We analyzed signals with continuous wavelet transforms as a function of recording site, task, and dystonia status, and evaluated changes in dystonia severity from DBS with mixed effects linear models.

Results: Dystonia was more common in our cohort versus historical estimates (61% at any time versus reported prevalence of 30%), with anatomical distribution in the leg/foot more commonly than hand or mouth. DBS activation was associated with significant improvement in the MDS-UPDRS painful ‘off’ dystonia item (MDS-UPDRS part 4.6, p=0.003), and trends toward improvement in BFM (p=0.10), and MDS-UPDRS  total score ‘off’ medication (MDS-UPDRS part III, p<0.001) were observed.

Conclusion: “Off” dystonia is underrecognized in PD motor symptoms that respond symptomatically to DBS. Cortical and subcortical field potentials show promise as potential biomarkers to identify dystonia and tailor treatment strategies with next-generation directional and adaptive DBS technologies.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/unlocking-dystonia-from-parkinsons-disease-pd-with-directional-deep-brain-stimulation-dbs/