Neuropsychological Outcomes of Long-Term STN-DBS in Parkinson's Disease: A Multidomain Study in a Turkish Cohort

Abstract This study aimed to evaluate the long-term neuropsychological outcomes and cognitive safety of bilateral subthalamic nucleus deep brain stimulation (STN-DBS) compared with standard medical therapy (MED) in patients with Parkinson's disease (PD). This single-center, cross-sectional study included 56 patients with idiopathic PD (STN-DBS = 32; MED = 24), all evaluated in the on-medication state under stable treatment conditions. A concise multidomain neuropsychological battery was administered, including phonemic and semantic verbal fluency, Stroop test (time, errors, corrections), forward and backward digit span, judgment of line orientation, clock drawing, and Mini-Mental State Examination. Clinical assessments comprised Unified PD Rating Scale part III, Hoehn–Yahr stage, PD Questionnaire-39, and Hamilton Anxiety and Depression scales. The two groups were matched for age, sex, education level, motor phenotype, and on-state motor severity, while disease duration was considered in comparative analyses. Compared with the MED group, patients with STN-DBS demonstrated lower phonemic verbal fluency, shorter forward digit span, and higher Stroop error counts. Differences in forward digit span and Stroop performance persisted after considering disease duration, whereas the phonemic fluency difference was attenuated. Semantic fluency, visuospatial abilities, and global cognitive performance did not differ between groups. Within the STN-DBS cohort, higher motor severity was associated with poorer semantic fluency and clock drawing performance, while no associations were observed between DBS duration and neuropsychological outcomes. Long-term STN-DBS is associated with selective modulation of attention and executive control functions, while global cognition, semantic fluency, and visuospatial abilities remain largely preserved. These findings support the relative cognitive safety of chronic STN-DBS and underscore the importance of routine executive function monitoring during long-term follow-up.