Deep brain stimulation for movement disorders: Patient selection and technical options
ABSTRACTDeep brain stimulation (DBS) is used as a treatment for movement disorders. Unlike ablative procedures, DBS is reversible and adjustable. It is approved in the United States for treatment of Parkinson disease (PD), dystonia, and tremor. This surgical procedure is considered safe and effective for the management of the motor symptoms of these disorders, although it does not cure the underlying conditions. Potential complications of DBS surgery include intracranial hemorrhage, infections, and complications related to the hardware. There may also be complications related to stimulation or programming, although these are usually associated with dosages of dopaminergic medications and are reversible. DBS is usually performed under conscious sedation with awake evaluation during intraoperative physiologic testing. Typically, the procedure is performed with stereotactic image guidance, using computed tomography or magnetic resonance imaging (MRI) for targeting. Surgery can be accomplished with stereotactic frames or frameless systems. Recently, intraoperative MRI guidance has become available and is an alternative to the traditional surgical procedure, allowing for implantation of the DBS device under general anesthesia.
Microelectrode recording
Physiologic verification of anatomic targets identified by imaging can be accomplished with microelectrode recording (MER). This technique involves placing fine, high-impedance electrodes through the target area, so that anatomic structures can be recognized by characteristic electrical activity of individual neurons or groups of neurons. The locations of the structures are identified and the lengths of the electrode trajectories through the different structures—as well as the gaps between these structures—are recorded. The distances are then compared with the anatomy and a best-fit model is created to infer the location of the trajectory in the target area. Additional MER penetrations are made in order to further delineate the anatomy. Once a location for implantation has been selected, the DBS lead is inserted into the target area.
Electrode implantation
Lead implantation is often performed under fluoroscopic guidance in order to ensure accuracy and stability. When implanted, the electrode may cause a microlesional effect, manifested by transient improvement in symptoms.
The DBS leads are then connected to external pulse generators and assessed for clinical benefits and side effects. Amplitude, pulse width, and frequency are adjusted to test the therapeutic window of stimulation (clinical improvement thresholds versus side effect thresholds). Some PD patients develop dyskinesia during test stimulation, which may be a positive indicator for lead location. If good effects and a therapeutic window are observed, the location of the lead is considered to be satisfactory and the procedure is completed.
Pulse generator implantation
During the final step of surgery, performed under general anesthesia, the pulse generator is implanted. The extension cable that connects the DBS lead to the implantable pulse generator is tunneled subcutaneously, connecting the DBS lead to the pulse generator in the chest.
Intraoperative, real-time MRI stereotaxis
Real-time intraoperative MRI has become available for DBS implantation with devices recently cleared for use by the FDA. The procedure, typically performed in a diagnostic MRI suite, uses MR images acquired during surgery to guide DBS lead implantation in the target area and to verify implantation accuracy.8
