Cognitive outcome after unilateral pallidal stimulation in Parkinson's disease

Objectives-Chronic high frequency electrostimulation of the globus pallidus internus mimics pallidotomy and improves clinical symptoms in Parkinson's disease. The aim of this study was to investigate the cognitive consequence s of unilateral deep brain stimulation. Methods-Twenty non-demented patients with Parkinson's disease (age range 38 -70 years) were neuropsychologically assessed 2 months before and 3 months after unilateral pallidal stimulation. The cognitive assessment included me asures of memory, spatial behaviour, and executive and psychomotor function . In addition to group analysis of cognitive change, a cognitive impairment index (CII) was calculated for each individual patient representing the pe rcentage of cognitive measures that fell more than 1 SD below the mean of a corresponding normative sample. Results-Neurological assessment with the Hoehn and Yahr scale and the unifi ed Parkinson's disease rating scale disclosed a significant postoperative r eduction in average clinical Parkinson's disease symptomatology (p<0.001). Repeated measures multivariate analysis of variance (using right/left side of stimulation as a between subjects factor) showed no significant postoper ative change in cognitive performance for the total patient group (main eff ect of operation). The side of stimulation did not show a significant diffe rential effect on cognitive performance (main effect of lateralisation). Th ere was no significant operation by lateralisation interaction effect. Alth ough the patients experienced significant motor symptom relief after pallid al stimulation, they remained mildly depressed after surgery. Analysis of t he individual CII changes showed a postoperative cognitive decline in 30% o f the patients. These patients were significantly older and took higher pre operative doses of levodopa than patients showing no change or a postoperat ive cognitive improvement. Conclusions-Left or right pallidal stimulation for the relief of motor symp toms in Parkinson's disease seems relatively safe, although older patients and patients needing high preoperative doses of levodopa seem to be more vu lnerable for cognitive decline after deep brain stimulation.