Deep brain stimulation (DBS) is a neuromodulation therapy treating symptoms of various neurological disorders, including Parkinson’s disease (PD), essential tremor, and dystonia. DBS acts much like a pacemaker for the brain: Electrodes placed in certain deep brain targets can be stimulated to modulate circuits and thus mitigate motor symptoms. DBS therapy traditionally uses a linear 4-contact lead positioned in select targets within the brain, e.g., subthalamic nucleus (STN), internal globus pallidus (GPi) or thalamus. After lead placement, stimulation parameters are programmed, which allow a variable-sized spherical field of stimulation that can move up and down the lead centered on the contacts. While DBS provides symptom relief, individual patients can still experience side effects caused by the electric field spreading into adjacent nontarget areas. New lead contact segmentation technology, with its 3 segments per row (Figure 1), promises to allow neurologists to more finely tune the electric field and better target desired areas while mitigating undesired stimulation (Figure 2).
Two recent case studies illustrate the use of DBS technology in patients with PD. One patient underwent pre-procedure screening and brain imaging, opting to get an advanced 7-Tesla MRI. The procedures employ advanced imaging and intraoperative neurophysiological mapping to define the target area’s borders for optimal lead placement. Patients are awake during part of the electrode implantation procedure.
Once the final target had been determined in this patient, the neurosurgeon placed the lead in the STN and performed an initial electrode screening. Leads were connected to an external pulse generator that delivers electrical pulses to each electrode. For each of the contacts, neurologists defined the “therapeutic window,” or range of pulse intensity producing clinical benefit without side effects. Doing so involves increasing the intensity of a particular contact or row of contacts until the first observed suppression of motor symptoms (which defines the lower limit) and then till the first occurrence of side effects (which marks the upper limit).
In this patient, suppression of symptoms occurred at a low amplitude. The amplitude was further increased, and at roughly twice the intensity, the patient described the onset of some side effects, likely due to spread of the larger electric field to the internal capsule, although the current was within the normal range by conventional standards.
With the new lead technology, neurologists were able to turn off the lead segment directed toward the internal capsule, allowing the current to be shifted away from that region and more medially without having to reposition the lead. This action caused the side effects to dissipate, and the therapy amplitude was increased on the remaining 2 active contacts on the row, allowing therapy to reach a greater region of tissue without causing side effects.
At the patient’s initial clinical programming session, we noted that the patient’s upper and lower limb tremor completely resolved when stimulation on the same contact row was set at roughly 1.25 mA. The patient described some sensations at 2mA. When the segments were set to steer away from the internal capsule, the side effects resolved, and the therapeutic window was increased to just over 3mA. With the new technology, the patient will have an expanded programming parameter and range of options should treatment needs change over time.
Patient 2. A second patient also underwent a DBS procedure employing the new lead technology but implantation was in the GPi. In Patient 2, after surgeons implanted the pulse generator at the first programming session, they noticed some capsular side effects during electrode screening for therapeutic window determination. In this case, with the lead in the GPi, the internal capsule lay medially, and while the patient had good benefit from DBS, further increases in amplitude were prevented due to the development of side effects caused by the spread of current into the internal capsule. When the electrode facing the capsule was turned off, the side effects resolved. The programmer was then able to increase the amplitude of stimulation and affect a greater amount of the GPi, further improving the therapeutic benefit without side effects.
Our initial clinical experience illustrates the value of having added latitude to allow for exploration of a wider range of stimulation parameters tailoring of therapies to individual patients.
New deep brain stimulation systems and imaging technology are allowing for more accurate placement of leads and more highly targeted therapy, improving quality of life for patients with Parkinson’s.Continue reading