- Neurosurgical Department, Klinikum Dortmund, Germany
- Department for Neurology, St. Joseph-Krankenhaus Berlin-Weiβensee, Germany
Correspondence Address:
Ali Harati
Department for Neurology, St. Joseph-Krankenhaus Berlin-Weiβensee, Germany
DOI:10.4103/2152-7806.121637
Copyright: © 2013 Harati A. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.How to cite this article: Harati A, Thomas Müller. Neuropsychological effects of deep brain stimulation for Parkinson's disease. Surg Neurol Int 20-Nov-2013;4:
How to cite this URL: Harati A, Thomas Müller. Neuropsychological effects of deep brain stimulation for Parkinson's disease. Surg Neurol Int 20-Nov-2013;4:. Available from: http://sni.wpengine.com/surgicalint_articles/neuropsychological-effects-of-deep-brain-stimulation-for-parkinsons-disease/
Abstract
Background:Putative changes of cognition after deep brain stimulation (DBS) in patients with Parkinson's disease (PD) are a matter of debate. The aim of this study was to assess cognitive abilities before and following bilateral subthalamic nucleus (STN) DBS and to review the available literature.
Methods:Twenty patients underwent bilateral DBS of the STN. Cognitive skills were assessed in a standardized fashion before and at least at 12 months after the surgical intervention.
Results:There was a significant decline of both semantic and phonematic verbal fluency and a mild trend for a deterioration of verbal memory after DBS. Mood, general cognitive screening, and visospatial abilities remained unchanged.
Conclusion:STN DBS in the treatment of PD has resulted in a significant reduction of motor symptoms and improved independence and quality of life in appropriately selected patients. However, it may have isolatable effects on verbal fluency and related function. Case series in the literature reported similar findings. Potential candidates for DBS should be counseled about the risk of mild cognitive declines.
Keywords: Cognitive decline, deep brain stimulation, memory, Parkinson's disease, subthalamic nucleus, verbal fluency
INTRODUCTION
Parkinson's disease (PD) is a common neurodegenerative motor disorder, clinically characterized by the progressive impairment of motor function and associated cognitive decline.[
PATIENTS AND METHODS
Patients
20 PD patients (13 men) participated in this trial. They received bilateral DBS of the STN. The selection criteria were clinically diagnosed PD, severe levodopa-related motor complications despite prior optimal adjustment of antiparkinsonian medication, no surgical contraindications, no dementia or major ongoing psychiatric illness and no other neurological disorders. The characteristics of the patients are summarized in
Surgical techniques
The procedures were staged in all patients with implantation of bilateral STN electrodes in one session and implantation of the pulse generators in a second session 3-5 days later. A Leksell stereotactic head frame (Elekta Instruments, Stockholm, Sweden) was placed. The dorsolateral (sensorimotor) portion of the STN was localized using a proportional geometric scheme based on the distance between the anterior commissure and the posterior commissure, as well as the location of the midcommisural point. The electrodes were implanted under local anesthesia during a single operative session, using a combined approach of intraoperative recording and stimulation. The electrode position was controlled either by postoperative computed tomography (CT) or magnet resonance imaging (MRI). The definitive quadripolar electrodes (model 3389; Medtronic) were connected to a subcutaneous programmable pulse generator (Kinetra; Medtronic) in the subclavicular area in a second operative session. Electrical parameters (pulse width, frequency, and voltage) were adjusted progressively using an electromagnetic programmer (7532 neurological programmer; Medtronic).
Cognitive and behavioral assessment
Cognitive assessment was carried out with an extensive neuropsychological test battery. It included:
Cognitive screening by the Mini Mental State Examination (MMSE)[ Verbal memory with a German version of the Rey Auditory Verbal Learning Test (verbal memory test [VLMT])[ Determination of amnestic disorders (Berlin amnesia test [BAT])[ Investigation of visospatial abilities by the Clock drawing test[ Performance of language phonological and semantic verbal fluency (“Regensburg verbal fluency test” [RWT])[ Execution of the Becks Depression Inventory (BDI).[
The raw scores were assessed for each patient. The raw scores for WMS-R, VLMT, RWT, BAT, and LPS were then adjusted for age-matched percentile-ranges.
Design
Cognitive assessment and a clinical interview, aimed at detecting the presence of behavioral abnormalities or psychiatric disorders, were performed preoperatively (during the week preceding electrode implantation) and postoperatively between 12 and 18 months after implantation. All cognitive and behavioral assessments before and after surgery were performed while the patients were on an antiparkinsonian medication. Postoperative cognitive and behavioral assessments were performed with stimulators turned on.
Statistical analysis
Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS version 13.0). The Wilcoxon rank sum test was applied for comparison between the mean scores preoperatively and at the postoperative assessment. A level of P < 0.05 was considered significant.
Ethics
Written informed consent was obtained from each subject. The local ethics committee of the university approved this study.
RESULTS
There was a worsening of verbal fluency and verbal digit span after DBS. Verbal memory declined compared with preoperative scores and deteriorated in two out of six items. The general cognitive screening and visospatial abilities remained unchanged. Mood was not altered [
DISCUSSION
Our results and the most consistent findings from the literature [
The variable frequencies of cognitive decline after STN DBS in the literature were caused by different ascertainment methods, patient selection criteria, operative techniques, and pre- and postoperative patient management strategies. Studies using formal and substantial neuropsychological evaluation were more likely to find changes than studies using undefined methods or simple cognitive screening instruments such as the MMSE.
Despite use of different assessment tools, STN DBS in most series was associated with decline of verbal fluency. Performance on verbal fluency might be disrupted in PD and consecutively predict incipient dementia.[
In conclusion, STN DBS independently affects verbal and nonverbal cognitive function.
STN DBS in the treatment of PD has resulted in a significant reduction of motor symptoms and improved independence and quality of life for most carefully selected patients. This procedure is associated with some risk for cognitive side effects beyond the expected rate of usual surgical complications such as hemorrhage or infection. The neuropsychological assessment must be considered essential to minimize such risks and to further our understanding of the underlying neurobiology and neuropsychological impact of these treatments.
ACKNOWLEDGMENT
The authors would like to thank Dr. Klotz and Dr. Cyron for scientific advice and support for the study.
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