Frequently Asked Questions about the Cognitive and Behavior Effects of Deep Brain Stimulation
Over the past two decades deep brain stimulation (DBS) has become an important tool in the treatment armamentarium for persons with Parkinson’s disease (PD). DBS involves placement by a neurosurgeon of electrodes within the brain that are connected to a pulse generator, akin to a cardiac pacemaker. Neurologists then program the device (for example, the amount of current and the location of the active electrode contacts) so that individuals experience the most benefit with the least side effects. Research, especially in the past decade, has lead to technical advances (for example, the ability to steer or direct current to a particular part of the target structure being stimulated) and a better understanding of the desired and adverse effects of DBS.
One of the most controversial areas of debate about DBS has been the frequency, nature and extent of cognitive, emotional and behavioral changes that can accompany DBS. Importantly, one also has to determine for whom DBS is an effective and safe therapy, and there continues to be much discussion about the appropriateness (and type) of DBS in persons with cognitive impairment, and to lesser extent, in persons with psychiatric disturbance accompanying PD.
Several review articles and meta-analyses have addressed these issues, but they are usually quite technical and address the nature and extent of cognitive and emotional changes after DBS of various targets such as globus pallidus and subthalamic nucleus. I recently reviewed studies of the neuropsychological aspects of DBS, including meta-analyses, but structured the review so that it addresses the questions I am frequently asked by persons with PD, their carepartners, neurologists, and neurosurgeons. Below are some key conclusions I drew in the review based on my interpretation of the data. No doubt, not all will agree with these conclusions and I urge persons considering DBS to pose these questions to their physicians and neuropsychologists before undergoing the procedure.
How common are cognitive and emotional changes after DBS? Serious cognitive adverse events are rare within the first 3 to 6 months of treatment, probably occurring in 1-2% of persons. The most common serious cognitive adverse event is confusion or delirium. Mild confusion probably occurs in about 10% of persons soon after DBS, but resolves. The most common emotional issue is depression, occurring in about 10% (5% requiring treatment, the other 5% not requiring treatment). Rates of cognitive and emotional problems are typically higher after 12-24 months, but this is probably a reflection of the natural history of the disease and other treatment complications rather than DBS per se.
Is DBS of one target safer than another? Small, uncontrolled studies, and some higher quality studies doing limited assessments in small samples have suggested that DBS of the globus pallidus might be safer than subthalamic DBS from a neuropsychological standpoint. Meta-analyses and higher quality randomized trials with larger samples doing head-to-head comparisons fail to support this belief. These studies show minimal if any differences in neuropsychological outcomes between pallidal and subthalamic DBS.
Is unilateral DBS neuropsychologically safer than bilateral DBS? Although one would expect the answer to this question to be obvious, it is not. Unfortunately there are few studies of persons undergoing staged DBS or comparing persons after unilateral and bilateral surgery. A handful of small sample studies suggest that unilateral surgery may be safer, but other studies suggest that whether surgery is done on the most affected brain hemisphere or the language-dominant hemisphere may be more important factors in whether cognitive decline is observed.
Is DBS appropriate for persons with mild cognitive impairment (PD-MCI)? Currently most centers performs DBS if a person has PD-MCI, but not dementia. Two retrospective studies found that the diagnosis of PD-MCI did not impact outcome, but that specific cognitive impairments did. For example, those with significantly poorer attention had longer hospital stays. While the number of persons with PD-MCI increases after relative to before surgery, we do not yet know whether the specific type (or severity) of PD-MCI prior to surgery has a bearing on outcomes.
Do neuropsychological changes impact quality of life? The data are equivocal; the two largest randomized trials drew different conclusions. In one study the cognitive changes had no impact on quality of life. In the other study, quality of life improved after DBS in both those with and without cognitive deterioration, but those with cognitive declines showed smaller gains in quality of life.
Do new techniques such as current steering or surgery under general anesthesia offer neuropsychological advantages or disadvantages? There is too little data to allow firm conclusions, but preliminary studies suggest that “awake” and “asleep” surgery have similar neuropsychological outcomes. One study even reported better verbal fluency (word generation) after asleep than awake surgery, but this finding awaits replication and its clinical meaningfulness is unknown.
Footnote: Persons interested in a more detailed and technical discussion, including a discussion of additional issues, are referred to:
Tröster, A.I. (2017). Some clinically useful information that neuropsychology provides patients, carepartners, neurologists, and neurosurgeons about deep brain stimulation for Parkinson’s disease. Archives of Clinical neuropsychology, 32, 810-828
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Alexander I. Tröster, PhD presented at the 2nd World Parkinson Congress in Glasgow, Scotland and the 3rd World Parkinson Congress in Montreal, Canada. He is currently a professor of neuropsychology and Chair of the Department of Neuropsychology at Barrow Neurological Institute.
Ideas and opinions expressed in this post reflect that of the authors solely. They do not reflect the opinions or positions of the World Parkinson Coalition®