Background: Stimulation-induced dysarthria (SID) is a troublesome and potentially therapy-limiting side effect of deep brain stimulation of the subthalamic nucleus (STN-DBS) in patients with Parkinson’s disease (PD). To date, the origin of SID, and especially whether there is an involvement of cerebellar pathways as well as the pyramidal tract, remains a matter of debate. Therefore, this study aims to shed light on structural networks associated with SID and to derive a data-driven model to predict SID in patients with PD and STN-DBS.
Methods: Randomised, double-blinded monopolar reviews determining SID thresholds were conducted in 25 patients with PD and STN-DBS. A fibre-based mapping approach, implementing the calculation of fibr-wise ORs for SID, was employed to identify the distributional pattern of SID in the STN’s vicinity. The ability of the data-driven model to classify stimulation volumes as ‘causing SID’ or ‘not causing SID’ was validated by calculating receiver operating characteristics (ROC) in an independent out-of-sample cohort comprising 14 patients with PD and STN-DBS.
Results: Local fibre-based stimulation maps showed an involvement of fibres running lateral and posteromedial to the STN in the pathogenesis of SID, independent of the investigated hemisphere. ROC analysis in the independent out-of-sample cohort resulted in a good fit of the data-driven model for both hemispheres (area under the curve (AUC)left=0.88, AUCright=0.88).
Conclusions: This study reveals an involvement of both, cerebello-thalamic fibres, as well as the pyramidal tract, in the pathogenesis of SID in STN-DBS. The results may impact future postoperative programming strategies to avoid SID in patients with PD and STN-DBS.

Jergas, H., Petry-Schmelzer, J. N., Hannemann, J., Thies, T., Strelow, J. N., Rubi-Fessen, I., Quinting, J., Baldermann, J. C., Mücke, D., Fink, G. R., Visser-Vandewalle, V., Dembek, T. A. & Barbe, M. T. (2024). One side effect – two networks? Lateral and posteromedial stimulation spreads induce dysarthria in subthalamic deep brain stimulation for Parkinson’s disease. Journal of Neurology, Neurosurgery and Psychiatry. https://jnnp.bmj.com/content/early/2024/08/15/jnnp-2024-333434.long.