Language and verbal fluency outcome after bilateral subthalamic Nucleus Deep Brain Stimulation in Parkinson's disease.

Background: Language disorders in Parkinson's Disease (PD) following bilateral subthalamic Nucleus Deep Brain Stimulation (STN-DBS) are common.

Objective: To assess STN-DBS impact on language and observe clinical and anatomical predictors of poor outcome.

Methods: We prospectively included PD patients undergoing STN-DBS. We performed a neuropsychological evaluation focusing on language before (V0), 3 days after (V1), and 3 months after (V2) surgery. Patients performed all assessments in ON drug condition, V1 with the stimulation turned OFF to evaluate the lesion effect, and V2 with the stimulation turned ON to evaluate the stimulation effect. Electrodes and active contact locations were determined with MRI-Atlas fusion. The stimulation parameters and the total electrical energy delivered (TEED) were recorded for each patient.

Results: 18 PD patients consecutively operated were included. We identified a decline in phonemic verbal fluency (VFP) at V1 and V2 (p = 0.023 and 0.032 respectively), as well as in semantic verbal fluency (VFS) (p = 0.025 and 0.019, respectively). There was a significant slowdown in the verbs naming test (p = 0.048). No other language alteration was recorded. There was no correlation between demographic or clinical factors and verbal fluency (VF) evolution. Active contact location within substantia nigra was associated with VFP worsening (p = 0.047), while elevated TEED on the left-sided electrode was associated with VFS decline (p = 0.021).

Conclusion: VF was significantly altered following STN-DBS. Location outside the dorsolateral sensorimotor STN, and high stimulation power appeared to promote this decline. Other language domains remained stable.