NEW YORK (Reuters Health) - When using a standard stereotactic technique for deep brain stimulation (DBS), the second brain lead implanted on the opposite side of the brain may not be placed as accurately as the first, according to research from Canada.
The order of electrode insertion during bilateral DBS may have a small impact on clinical outcomes due to increased electrode dispersion on the second implanted side, the study team reported online September 9 in the Journal of Neurology, Neurosurgery & Psychiatry.
"This study proves that the implantation of the second hemisphere is slightly less accurate than the first one," Dr. Alfonso Fasano of the Movement Disorders Center at Toronto Western Hospital told Reuters Health by email.
Dr. Fasano and colleagues analyzed clinical and radiographic data on 76 patients, aged 58 years on average, with Parkinson's disease. The participants underwent surgery at one academic medical center and completed at least one year of follow-up.
The researchers calculated electrode location dispersion as the square of the deviation from the population mean, and they analyzed the deviation direction by comparing the intended and final implantation coordinates. They analyzed the predictors of postoperative motor condition improvement by linear regression, controlling for electrode implantation sequence.
Compared with the first side, the second-side electrode tip had significantly higher dispersion as an overall effect (5.6 vs 2.2 mm2, p=0.04), or along the X-axis (4.1 vs 1.4 mm2, p=0.03) and the Z-axis (4.9 vs 2.9 mm2, p=0.02).
Second-side stimulation was associated with lower threshold for side effects (contact 0, p<0.001 and contact 3, p=0.004). In linear regression, baseline activities of daily living (p=0.010) and electrode dispersion on the second side (p=0.005) were significant outcome predictors.
"This large study, with rigorous documentation of lead location and implantation using the same procedure in all cases, confirms suspicions previously held in the movement disorders community," Dr. Kelly Mills, of the Parkinson's and Movement Disorders Center at Johns Hopkins in Baltimore, Maryland, told Reuters Health by email.
"The authors do a good job of proposing several explanations for lead location variability, including brain shift, pneumocephalus, ventricular enlargement, difficulty in X-ray visualization of the second electrode due to the presence of an existing electrode, and decreased cooperation by the patient as he or she fatigues during surgery," he said.
"It is important that this study was performed by an experienced DBS team, and that lead location variability might be even higher at less-experienced centers or when using other surgical techniques," added Dr. Mills, who was not involved in the study.
Dr. Alon Mogilner, director of the Center for Neuromodulation at New York University Langone Medical Center in New York City, told Reuters Health by phone, "Patients with Parkinson's disease undergoing DBS usually have Parkinson's on both sides of their body, so they need to have the surgery on both sides of their brain."
The left- and right-sided electrodes can be placed on the same day or a few days, weeks, or months apart, explained Dr. Mogilner, who was not involved in the study.
"The advantage of inserting electrodes on the same day is one less hospital stay for the patient, but the outcomes may not be as good," he cautioned.
One possibility to explain the study findings is that the brain actually moves, Dr. Mogilner told Reuters Health. "You drill a small hole in each side of the head, and all you can see are the two holes. You cannot see the brain moving, and between the time it takes you to insert the first and second electrodes, it may shift. A 'brain shift' of only a millimeter or so can be clinically significant."
Dr. Mogilner advised that surgeons implant the electrodes on different days or use intraoperative magnetic resonance imaging (MRI) scans to help them accurately place both electrodes on the same day.
"In the U.S., maybe 25% of centers now use intraoperative imaging," Dr. Mogilner said, but he predicts this technique to become more common over the next few years.
"The most important predictor of outcome after DBS is accurate location of the brain electrodes. Nothing substitutes for accurately placed electrodes," he said.
The authors reported no funding or conflicts of interest.
SOURCE: http://bit.ly/1iWYQDI
J Neurol Neurosurg Psychiatry 2015.
http://www.medscape.com/viewarticle/851743?src=wnl_edit_tpal
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