Supplementary Material for: Preoperative Brain Atrophy as a Predictor of Motor Outcomes After STN Deep Brain Stimulation in Parkinson’s Disease

Background Brain atrophy is common in Parkinson’s disease (PD) and contributes to motor and cognitive decline. However, the predictive value of neuroimaging-based volumetric measures for motor outcomes following deep brain stimulation (DBS) remains unclear. This study examines whether preoperative volumetric assessment can predict motor outcomes after subthalamic nucleus (STN) DBS in PD. Methods Preoperative T1-weighted 3D MP-RAGE MRI scans were analyzed to measure subcortical, ventricular, and cortical volumes using Brainlab software. Motor outcomes were assessed by changes in the Movement Disorder Society - Unified Parkinson’s Disease Rating Scale part III (MDS-UPDRS-III) scores pre- and postoperatively in 39 participants. Stepwise logistic regression was performed to determine associations between brain volumes and DBS response. Results Smaller substantia nigra compacta volume (0.81 [IQR 0.74-0.85] vs 0.72 [IQR 0.69-0.73]), larger ventricular system (26.1 [IQR 21.4-30.05] vs 34.1 [IQR 28.6-40.87]), and lower atrophy ratio (41.76 [IQR 37.59-50.71] vs 29.63 [IQR 25.9-36.55]) were significantly associated with reduced motor improvement following STN-DBS. The predictive model based on these values demonstrated excellent performance (AUC 0.95, 95% CI: 0.87–1; p < 0.01) in forecasting poorer DBS treatment outcomes as measured by the MDS-UPDRS-III scale. Conclusions Our findings highlight the impact of enlargement of ventricular system and brain atrophy, particularly of the substantia nigra, on motor outcomes after STN-DBS. The association between atrophy measures and executive dysfunction suggests that subclinical dementia may underlie poor DBS response. Future studies should further explore the role of neurodegeneration in DBS response to optimize patient selection and electrode targeting.