Objective:

To determine whether demographic cognitive selection bias exists when choosing between STN and GPi as targets for DBS. 

Background:

Though globus pallidus interna (GPi) is reportedly similarly effective to subthalamic nucleus (STN) DBS, offers primary dyskinesia reduction, and has been associated with less postoperative cognitive decline, STN is more frequently selected at many sites. This could be due to an impression that STN is more effective or programmable in practice. We hypothesized this could result in patients thought to be at greater cognitive risk, or with fewer comorbidities, selectively being recruited to GPi vs STN DBS. 

Design/Methods:

We analyzed the pre-DBS demographic and baseline cognitive data of 127 patients who underwent neuropsychological evaluation. We compared performance in global functioning, verbal learning, verbal memory, confrontation naming, phonemic fluency, and semantic fluency between the STN and GPi groups using t tests. 

Results:

95 STN & 32 GPi implants comprised our cohort. The pre-DBS GPi population was younger (57.6 ± 9.5) compared to STN (63.3 ± 8.6), p = .005. STN patients performed better in semantic fluency as measured by T scores, 50.75 versus 44.28 for the GPi group (p = 0.01). We found no significant difference in disease duration or other cognitive domains analyzed. 

Conclusions:

We found that subjects selected for GPi DBS had worse semantic fluency performance, but other cognitive measures did not differ. Global cognitive performance does not appear to drive DBS selection at our center. Patients selected for GPi targets did not differ in disease duration or severity; however, they were younger. Further investigation will be required to see if phenotype, or psychiatric or medical comorbidities, affect selection. The many preoperative variables (cognition, mood, medication burden, dyskinesia) highlight the importance of an interdisciplinary approach to target selection and a comprehensive analysis of symptoms and risk-benefit profile.