Objective:

To investigate if time since Deep Brain Stimulation (DBS) surgery is correlated with various neuropsychological outcomes across multiple cognitive domains in patients with Parkinson’s Disease (PD).

Background:

DBS provides substantial motor benefit in PD but has variable nonmotor outcomes. Evolution may depend on time elapsed since implantation. Understanding how cognitive performance evolves over time may clarify whether observed changes reflect transient surgical effects, stimulation-related adaptation, or progressive disease processes.

Design/Methods:

We conducted a retrospective analysis of patients with Parkinson’s disease who underwent bilateral DBS implantation and completed neuropsychological testing preoperatively and at approximately one year postoperatively. Correlation analyses were performed between months since surgery and change scores on the entire standard neuropsychological battery, including the Wechsler Adult Intelligence Scale–IV (WAIS-IV) subtests: Digit Span Total, Longest Digit Span Forward (LDSF), Longest Digit Span Backward (LDSB), Digit Sequencing, and Longest Digit Span Sequencing (LDSS).

Results:

A cohort of 61 DBS patients (53 STN, 8 GPi), before and 1-year after surgery was analyzed. Average age was 68.6, average disease duration 10.32 years, average OFF UPDRS part III 42.4, ON 16.6 at time of presurgical evaluation. A higher number of months since surgery strongly correlated with improvement in WAIS-IV Digit Span Total (r=0.55), LDSF (r=0.62), LDSB (r=0.58), Digit Sequencing (r=0.51), and LDSS (r=0.63). Other cognitive domains showed no significant correlation with months since surgery.

Conclusions:

Time elapsing following DBS surgery appears to measurably correlate with working memory indices, suggesting that these measures continue to evolve past the early postoperative period. Surprisingly, these particular findings were shown to improve over a longer duration of time, possibly due to reduction in motor symptoms, leading secondarily to decreased distractibility and mood symptoms. Such information potentially guides psychosocial management and calls for a closer more granular follow-up of certain neuropsychological tests. Additional studies could attempt to differentiate stimulation-related recovery from disease progression.