Introduction: Deep brain stimulation of the subthalamic nucleus (STN) is an effective therapy for patients with Parkinson’s disease (PD). Different regions within the subthalamic area have been correlated with optimal clinical outcomes and undesired side effects. In this work, we correlate the motor outcome in PD patients with the degree of nigrofugal fiber stimulation.
Methods: Thirty-five patients with STN-DBS were included and their clinical and stimulation parameters were recorded at one-year follow-up. The volume of activated tissue (VAT) for all patients was modelled using finite element method within the Lead-DBS software. All VATs were summed and analyzed using generalized linear models in FSL software to obtain statistically significant stimulation clusters (StimC) correlated with: greater reduction of dopaminergic medication, improvement in Unified Parkinson's Disease Rating Scale (UPDRS) III, bradykinesia, and rigidity scores. Nigrofugal pathways (nigroputaminal and nigropallidal) were obtained using probabilistic tractography with imaging data from 35 PD matched subjects from the Parkinson's Progression Markers Initiative connectome. Finally, we calculated the overlap of StimC with the nigrofugal fibers and STN.
Results: Significant reduction of symptoms was obtained with STN-DBS in our patients (p<.05). Nigroputaminal and nigropallidal pathways were traced as described in previous anatomical descriptions. StimC with the greatest dopaminergic medication reduction overlapped with the nigroputaminal fibers (coeff0.50) and not with the STN. StimC with the greatest UPDRS improvement showed more overlap with nigroputaminal and nigropallidal pathways (coeff0.49,0.38) than the STN (coeff0.05). Two StimC with greater bradykinesia improvement overlapped with the nigropallidal fibers (coeff0.55) and the STN (coeff0.19). Finally, two distinct StimC correlated with greater rigidity improvement overlapped with nigroputaminal fibers (coeff0.30) and the STN (coeff0.26).
Conclusions: Electrical field involvement of the nigroputaminal fibers, more than the STN, appears to produce the most improvement in UPDRS III, rigidity, and reduction of dopaminergic medications. Similarly, nigropallidal fibers involvement is associated with greater bradykinesia improvement.
Patient Care: Improving STN targeting and programming
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the tractography anatomy of the nigrofugal fibers. 2)Discuss potential explanations of certain effects of STN-DBS. 3)Identify sub-regions in the subthalamic area associated with outcomes.