Regression-based thresholds to detect clinical changes in verbal fluency after STN-DBS in Parkinson's disease

Introduction: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves motor functions in patients with Parkinson's disease (PD) but may cause a decline in specific cognitive domains including executive processes and language. The aim of this study was to derive standardized regression-based (SRB) reliable change indices (RCIs) in an Italian cohort of Parkinson's patients undergoing STN-DBS to detect clinically meaningful variations in verbal fluency (VF) one year after surgery define. Methods: Before (T0) and 12 months after (T1) surgery, 36 PD patients who underwent bilateral STN-DBS were evaluated with the Alternate Verbal Fluency Battery (AVFB), including phonemic (PVF), semantic (SVF) and alternate VF tests (AVF) and a composite shifting index (CSI). At T0, motor status was assessed using the Unified Parkinson's Disease Rating Scale-III (UPDRS-III) and L-dopa equivalent daily dose was recorded. Results: Group-level declines were limited to PVF and SVF scores. Applications of these RCIs revealed idiosyncratic patterns of longitudinal trends that differed from those at the group level. Indeed, when looking at individual performances, no clustered pattern of decline or improvement could be visibly detected. The UPDRS-III predicted T1 AVF and CSI scores. Conclusion: Our study provides Italian practitioners and researchers with SRB-RCIs to detect meaningful differences in the VF performance of PD patients undergoing STN-DBS one year after surgery. Variables associated with postoperative cognitive changes can be used in future studies to develop multivariable predictive models to support clinical decision making and patient counselling.