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NEUROSURGERY ARTICLESProgramming Deep Brain StimulatorsDeep brain stimulation (DBS) is rapidly becoming the gold standard for surgical management of symptoms of Parkinson’s disease, essential tremor, and dystonia. Numerous clinical trials are underway to assess the safety and efficacy of DBS in other conditions such as epilepsy, obsessive-compulsive disorder, depression, coma, obesity, cluster headache, and Tourette’s syndrome. While the target in the brain is different for many of the above conditions, programming is performed in the same manner using different settings for voltage, pulse width, frequency, and electrode contact selections to shape and control the electrical field.
How does DBS work? Electrodes are placed directly into the brain tissue. The targets are the ventral intermediate (VIM) thalamus for essential tremor, subthalamic nucleus (STN) for Parkinson’s disease, and the globus pallidus internus (GPi) for dystonia. Brain tissue is stimulated through the application of an electrical impulse, which spreads through the tissue with a specific pattern and shape.
By adjusting the voltage, more or less brain tissue can be stimulated (Figure 3). By elongating the pulse duration, the time the electrical impulse is applied to the neural elements is prolonged, activating more tissue within the target area. Frequency is another tool in the clinician’s toolkit. By increasing the frequency, impulses can add to each other and build up more stimulation in the same time period. We can also choose the activation mode: “unipolar” or “bipolar.” Unipolar mode creates the largest electrical field, which radiates out from the center of the electrode. Bipolar mode creates a narrower and stronger field of stimulation, which can help to avoid side effects.
Because of all of these things, DBS programming is an art. It takes considerable time and patience on the part of the clinician and the patient. In particular, on the first visit all of the electrode contacts must be tested in detail. This may take an hour or more. With patients on Parkinson’s medications, side effects may actually increase during “on” periods, causing dyskinesias or dystonic posturing. The clinician will adjust the medication and reprogram the DBS, fine tuning until a good combination is achieved. Additional programming occurs in the ensuing weeks to ensure the best therapeutic effect and fewest side effects. One final consideration is to use the lowest voltages possible to maximize battery life. In certain progressive diseases (e.g. Parkinson’s disease) frequent reprogramming may be necessary. In certain other conditions (e.g. dystonia), it may take weeks to months to achieve the desired effect from stimulation, therefore programming is only performed monthly. Every patient should be aware that programming may take several visits over the course of a few months. Together, we will work to understand each patient’s individual response to stimulation in order to achieve the best mobility and quality of life. |
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The hardware that is implanted consists of: (1) an electrode with four contacts (each contact is 1.5mm long with either 1.5mm or 0.5mm spacing between contacts); (2) an extension lead that connects the electrode to the (3) implantable pulse generator (IPG) in the subcutaneous tissue over the chest wall (Figure 1).
Through programming the voltage (amplitude), frequency, pulse duration, and shape of the charge, the amount of brain tissue stimulated can be precisely controlled (Figure 2).
Best results from deep brain stimulation with few or no side effects is made possible by accurate placement of the electrode in the specific brain target for the disease being treated. However, some of these targets are very small; for example, the STN is about the size of an M&M. Placing the electrode slightly off the target can cause it not to work well, or lead to side effects such as slurring of speech, pulling of face or arm muscles, or tingling in hands or face.