Objective: To determine rates of mild cognitive impairment in Parkinson’s disease (PD-MCI) before and after deep brain stimulation (DBS) and to identify the specific cognitive alterations potentially driving change in PD-MCI diagnosis.

Background: One small-sample (n=30) study and not using MDS PD-MCI criteria reported an increase in MCI from 47% to 63% an average of 9 months after subthalamic (STN) DBS relative to pre-surgical baseline. The impact of pre-operative MCI on post-surgical neuropsychological diagnostic outcome has not been detailed, and it is unknown whether specific cognitive alterations drive PD-MCI diagnostic change (i.e., resolution or development of PD-MCI) after DBS.

Methods: We report on 117 consecutive uni- (n=23) or bilateral (n=94) STN or pallidal (GPi) DBS (22 awake, 95 asleep) cases who underwent neuropsychological (NP) evaluation before and about 9 months after DBS. NP test battery covered overall level of cognitive functioning and included at least two tests of attention, executive and visuoperceptual functions, language and memory. Quality of life (QoL) and psychiatric/emotion rating scales were also included. Test-retest interval was on average 12 months. PD-MCI was diagnosed using the MDS Level II criteria.

Results: Subjects included 68 STN and 49 GPi DBS patients, average age 66.8 and 64.4 years, disease duration 7.4 and 10.3 years, UPDRS-III off/on medication 42.6/23.5 and 35.3/18.7, respectively. Prior to surgery 47.9% of the sample had PD-MCI, and this increased slightly to 54.7% after DBS, with the proportions of those having vs. not having PD-MCI before and after surgery not differing significantly (Chi-square p>0.30). In both the STN and GPi groups, the proportion of those not changing PD-MCI diagnoses was greater than those changing diagnosis after DBS (STN: 47 unchanged, 9 resolved, 12 new PD-MCI diagnoses after DBS; GPi: 36 unchanged, 4 resolved, 9 new PD-MCI diagnoses; Chi-square ps<0.002). However, proportions of those unchanged, improved or declined were similar across STN and GPi groups (Chi square p=0.69). In GPi DBS, declines (de novo PD-MCI after DBS) were driven by significant mean score declines in category verbal fluency and on the Stroop task. In STN, those developing PD-MCI showed declines in letter and semantic verbal fluency, aspects of executive functions, and list learning.

Conclusions: Similar and small proportions of patients develop PD-MCI after STN and GPi DBS, but diagnostic change may be driven by different (albeit overlapping) cognitive alterations after STN and GPi DBS.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mild-cognitive-impairment-in-parkinsons-disease-before-and-after-deep-brain-stimulation/