Neuropsychological Outcomes After Deep Brain Stimulation for Parkinson Disease

VBCN - May 2015 Volume 2, No 1

An in-depth analysis from the randomized, controlled Netherlands Subthalamic and Pallidal Stimulation (NSTAPS) clinical trial found no substantial differences in neuropsychological outcomes in patients with Parkinson disease who received globus pallidus internus (GPi) deep brain stimulation (DBS) or subthalamic nucleus (STN) DBS. The only differences observed 12 months after DBS were small, reported Vincent J. Odekerken, MD, and colleagues, who analyzed these outcomes and investigated whether baseline parameters could predict cognitive decline (Odekerken VJ, et al. Neurology. 2015; 84:1355-1361).

There has been lingering concern about cognitive decline following DBS. In particular, STN DBS has been associated with unfavorable outcomes, although data directly comparing STN DBS and GPi DBS, which are both effective in treating motor symptoms and dyskinesias, have been limited. The NSTAPS clinical trial indicated greater functional improvement during the medication off-drug phase with STN DBS compared with GPi DBS. In addition, the NSTAPS clinical trial showed no difference between the groups on a composite score for cognition, mood, and behavior. These findings conflict with several previous studies, which showed more cognitive problems with STN DBS versus GPi DBS.

This current analysis focused on the results of the extensive battery of neuropsychological tests used for the cognitive evaluation of the study’s 128 patients. There were significant differences in Stroop word reading, Stroop color naming, Trail Making Test Part B, and Wechsler Adult Intelligence Scale similarities, with STN DBS showing greater negative change than GPi DBS. The effect sizes of these differences, however, were small to medium.

“These results suggest a larger decline in mental speed, attention, and possibly language after STN DBS, however, this effect was not reproduced on the Trail Making Test Part A (TMTA) and Stroop color-word interference, respectively. These differences in cognitive change are similar to previous randomized controlled trials comparing GPi DBS and STN DPB,” the researchers reported.

There was no significant difference between the 2 groups regarding cognitive decline based on the composite score after DBS. Following GPi DBS, 29.3% of patients experienced cognitive decline; after STN DBS, 39.3% experienced decline (P = .26). In a logistic regression model, age at baseline (P = .003) and semantic fluency at baseline (P = .032) were independent predictors of cognitive decline after DBS. No satisfactory explanation was found for the association with baseline semantic fluency. Although a stable predictive model could be helpful to physicians in selecting treatment, the authors reported that “the results from our regression analysis, as well as the variation in predictors between different studies thus far, suggest that these models for predicting cognitive outcome are unstable.”

The quality-of-life scores were not significantly different among patients demonstrating cognitive decline at 12 months and those who did not; in fact, the quality of life seemed to improve in patients with or without cognitive decline.

João Massano, MD, University of Porto in Portugal, wrote in an accompanying comment to the article, “This important research shows that STN DBS does not associate with substantial cognitive safety issues in comparison to GPi DBS, at least in cognitively intact patients. In addition, current evidence suggests that STN DBS conveys higher efficacy regarding motor symptoms and disability, lower battery depletion, and larger dopaminergic drug reduction. These data support STN as the preferred DBS target in most patients with Parkinson disease.”

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