Bilateral Implantation In Parkinson's Disease

Parkinson’s disease (PD) occurs in 1 to 2% of the people over 60 years, and estimated costs of drug treatment are about 1,000 to 6,000 dollars per patient per year1. Subthalamic deep brain stimulation (STN DBS) is a now commonly used method in which two electrodes are implanted in a patient’s subthalamic nuclei to decrease the motor symptoms and instabilities of the medication in PD. Usually there are two electrodes implanted, one in each hemisphere, even though PD occurs asymmetrically. That would make it logical to think that a unilateral implantation could be successful as well2. Bilateral implantations have shown more decrease of the motor symptoms and can often be implanted in one procedure, but are related to more cognitive impairment.
Complications like speech difficulties and postoperative confusion are not uncommon1. The working memory of patients might be affected by PD, possibly through changed basal ganglia output or altered mesocortical dopaminergic pathways, but they might even be worsened by bilateral DBS3. The pattern that has arisen shows that mostly the tasks that ask for greater cognitive control are very susceptible to the negative effects of DBS.
Studies have shown that unilateral STN DBS was also effective in improving the motor functions of PD patients. However, it has not been associated with these cognitive events4. The differences are probably caused by the asymmetry of the disease, which can modify the effect of bilateral STN DBS on working memory and other cognitive functions.
Therefore, it is important that more research is done on the exact difference between the cognitive impairments of bilaterally and unilaterally treated patients. This way a more precise selection can be performed before patients undergo the surgery, to ensure that it will have the best effect possible.