Objective: To compare the cognitive effects of GPi versus STN deep brain stimulation for PD in patients with moderate cognitive impairment.

Background: Patients with moderate cognitive impairment are considered borderline candidates for DBS surgery. Most RCT comparing the cognitive effects of GPi versus STN DBS in PD (1, 2) included only patients with no cognitive impairment. Although both targets are generally considered cognitively benign and similar in terms of motor benefit, STN DBS has been associated with a selective decline in frontal subcortical cognitive functions.

Methods: Retrospective case-control study, including all the patients who went through GPi DBS surgery for PD in a reference center and 1:1 controls, matched for age at surgery and pre-op DRS (Dementia Rating Scale)-2 score percentile. DRS-2, MMSE (Mini Mental State Examination), FAB (Frontal Assessment Battery) and verbal fluency were assessed at 6, 18 and 60 months.

Results: A total of 20 patients were included. The mean years of school was 6.15 and the mean age at surgery 63. The mean disease duration was 13 years and the mean UPDRS part III score OFF medication was 43. The median follow-up time was 18 months. There were no differences between the groups regarding this baseline variables. The mean DRS-2 baseline score was 123.20 for the GPi group and 128.00 for the STN group (p=0.294).

For the total of patients, there was a decline in semantic verbal fluency at 18 months (13.08 vs. 10.75, p=0,019). Both in the STN and the GPi groups separately, verbal fluency was the only neuropsychological measure that showed a significant variation at the different time points. Besides that, the semantic fluency score at 18 months was worse for the STN group (8.20 vs. 12.57, p=0.032)

There was no difference between groups regarding motor outcome (70.14% vs. 78.16%, p=0.103) but the STN group showed a greater reduction in dopaminergic therapy (36.81% vs. 62.97%, p=0.029).

Conclusions: In our experience, there is no cognitive advantage in choosing GPi over STN as a DBS target in patients with moderate cognitive impairment except for the verbal fluency, which seems to be more adversely affected in the STN group. What is more important, our findings encourage the eligibility of this patients for surgery, since they have the expected motor benefit without significant accrual of their cognitive impairment.

References: (1) Wang J-W, Zhang Y-Q, Zhang X-H, Wang Y-P, Li J-P, Li Y-J (2016) Cognitive and Psychiatric Effects of STN versus GPi Deep Brain Stimulation in Parkinson’s Disease: A Meta-Analysis of Randomized Controlled Trials. PLoS ONE 11(6): e0156721. doi:10.1371/journal.pone.0156721

(2) Odekerken VJ, Boel JA, Geurtsen GJ, Schmand BA, Dekker IP, de Haan RJ, Schuurman PR, de Bie RM; NSTAPS Study Group. Neuropsychological outcome after deep brain stimulation for Parkinson disease. Neurology 2015;84:1–7

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cognitive-effects-of-gpi-versus-stn-deep-brain-stimulation-in-parkinsons-disease-experience-with-patients-with-moderate-cognitive-impairment/