gms | German Medical Science

Objective: Deep brain stimulation of the subthalamic nucleus (STN-DBS) is an established therapy for Parkinson’s Disease. Unfortunately, individual outcomes vary and often residual gait disturbances ameliorated mobility. The exact lead localisation and stimulation parameters may be responsible for this aspect. So far, no study has been able to identify an "optimal efficacy volume" in respect of mobility and gait for DBS within the STN.We investigated Volumes of Tissue activated (VTA) in subjects with Parkinson’s Disease undergoing STN-DBS. We aimed to distinguish anatomic areas that, affected by DBS, have a positive effect on gait.

Methods: 86 subjects with idiopathic Parkinson’s Disease (Hoehn & Yahr 2.90.7, UPDRS III 48.712.3,disease duration 16.04.8 years) undergoing bilateral STN-DBS were stratified for motor improvement. To take a closer look at gait disturbances, we divided our subjects into groups according to their change in gait items of UPDRS III. To correlate the clinical outcome with the exact anatomical location of stimulation, we simulated VTAs in subject’s related MRI space and associated them with gait alterations. All patient images were registered to a common MNI-space. Only voxels that were overlapped by ≥6 VTAs were visualized to define a volume, where DBS has a positive effect on gait disturbances (="sweetspot").

Results: Our cohort shows motor improvement of 51.13% by stimulation alone (reduction of 24.913.2 points in UPDRS III). 24 subjects experienced a complete remission of gait problems by STN-DBS, meanwhile 9 subjects show de-novo gait disturbances. We observed no differences in stimulation parameters and global parkinsonism. Interestingly, the anatomic area of stimulation allows a clear separation of the groups. For individuals with an improvement of gait by DBS, the most commonly stimulated area was located more dorsal and antero-medial than the spot stimulated in individuals with a worsening of gait problems. Stereotactic coordinates for the centre of mass in improvement on gait were L=13.1, A=2.5, I=3.0 and coordinates for aggravation of gait problems were L=14.2, A=1.2, I=3.2.

Conclusion: We were able to show that the exact anatomical localisation of stimulation is correlated with gait alterations. The most beneficial spot to stimulate is located more dorsal and antero-medial, within the transition zone of the sensory-motor part of the STN and bordering white matter. In the future, these results could improve re-programming attempts in STN-DBS with gait problems.