Prospective open-label study links brain MRI to impulse control changes after DBS for Parkinson's.

Background: Subthalamic deep brain stimulation (STN-DBS) represents an established therapeutic intervention for advanced Parkinson's disease (PD), alleviating motor and non-motor symptoms. However, impulse control disorders (ICDs) present a complex challenge, with some patients experiencing postoperative improvements while others develop treatment induced impulsive-compulsive behaviours (ICB). The mechanisms determining these variable outcomes remain poorly understood, highlighting the need to predict postoperative ICB outcomes. Methods: This prospective open-label study aimed to identify microstructural markers associated with postoperative changes in impulsive-compulsive behaviour following STN-DBS. Thirty-five patients underwent diffusion MRI and clinical evaluations preoperatively and six months postoperatively. A whole-brain voxel-wise analysis utilising diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) was conducted to explore associations between microstructural metrics and changes in the Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease-Rating Scale (QUIP-RS). Results: Intact microstructure in frontolimbic WM tracts, including the cingulum, insular cortex connections, and major association fibres, was associated with greater postoperative reductions in impulsive-compulsive symptoms. Conversely, intact microstructure in specific grey matter areas including paracingulate gyrus, insular cortex, and precentral gyrus were associated with lower reductions or increases in postoperative ICB. Conclusion: These findings demonstrate that preoperative microstructural integrity within frontolimbic circuits and executive control networks associates with susceptibility to treatment-emergent impulsive-compulsive behaviours following STN-DBS. The convergent evidence from multiple diffusion metrics suggests that diffusion MRI may serve as a valuable tool for identifying patients at risk for developing ICB, potentially enhancing preoperative counselling and enabling targeted behavioural monitoring strategies.