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Deep brain stimulation for movement disorders: Patient selection and technical options

July 1, 2012|Cleveland Clinic Journal of Medicine
Andre G. Machado, MD, PhD;Milind Deogaonkar, MD;Scott Cooper, MD, PhD
Author and Disclosure Information

Andre G. Machado, MD, PhD
Center for Neurological Restoration, Cleveland Clinic, Cleveland, OH

Milind Deogaonkar, MD
Center for Neurological Restoration, Cleveland Clinic, Cleveland, OH

Scott Cooper, MD, PhD
Center for Neurological Restoration, Cleveland Clinic, Cleveland, OH

Correspondence: Andre Machado, MD, PhD, Center for Neurological Restoration, Cleveland Clinic, 9500 Euclid Avenue, S31, Cleveland, OH 44195; machada@ccf.org

Dr. Machado reported ownership interest in ATI Medical Equipment Corporation, Cardionomics, and Intelect Medical, Inc.; and consulting services for Monteris Medical. Dr. Deogaonkar reported intellectual property rights with Autonomic Technologies, Inc. and consulting for Medtronic, Inc. Dr. Cooper reported that he has no financial interests or relationships that pose a potential conflict of interest with this article.

This article is based on Dr. Machado’s presentation at “The Annual Therapy Symposium on Movement Disorders for the Modern Clinician” held in Fort Lauderdale, Florida, on January 29, 2011, and was written by Drs. Machado, Deogaonkar, and Cooper.

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.

Treatment outcomes depend on etiology

After programming, DBS can provide PD symptom control similar to that of medication “on time,” but with fewer on-off fluctuations and less on-time dyskinesia. Good surgical candidates are patients who once responded well to dopaminergic medications but who, after several years with the disease, present with increased duration of “off time,” unpredictable duration of on time, and medication side effects such as on-time dyskinesia. Patients who do not respond well to levodopa even in subscores of the UPDRS may not be good candidates for DBS, and in some cases the diagnosis itself needs to be reviewed.

Deep brain stimulation can improve quality of life and alleviate symptoms of essential tremor. Tremor control is best for the upper extremities and tends to be better for distal tremors than for proximal ones. Patients who are good candidates for surgery often have severe tremors. A substantial improvement in these symptoms often has a dramatic, positive effect on work and quality of life. In some patients, surgery is considered for mild tremor if it seriously disrupts the patient’s lifestyle or occupation and cannot be well controlled with medications. Often, in these cases, tremor that appears relatively mild to the examiner is significantly limiting for the patient.

Very severe and proximal tremor is more refractory, though it may also improve. The changes can be well documented with objective measures. In these cases, however, residual tremor can still be moderate to severe and can be functionally limiting. Head or vocal tremors are typically refractory. They may be improved with bilateral implantation, but this cannot be accurately predicted. Patients who present with head-only or head-predominant tremor are thought to be less likely to benefit than those with limb tremor. Nonetheless, tremors of the head can severely impair quality of life. Because there are few other treatment options, some patients choose DBS with the understanding that the outcome is uncertain and the benefit may be limited.

Tremor resulting from multiple sclerosis or other causes can be medically refractory and disabling. In our experience, DBS can be an off-label option for managing secondary tremors and good outcomes have been observed. However, outcomes are much less predictable and tremor control less effective than in patients with essential tremor.

Patients with primary generalized dystonia can be considered candidates for DBS and may experience improved symptom control and quality of life.4 Patients with the DYT1 mutation are more likely to respond well to DBS, as are those with other forms of primary generalized dystonia. In contrast to that seen in patients with PD and tremor, symptomatic improvement is frequently not observed during intraoperative testing. Several months of stimulation and programming may be required before significant improvements are detected.5 Surgery can also be considered for off-label use in the treatment of patients with secondary dystonia—such as that following injury or associated with cerebral palsy—but outcomes are less predictable and usually more limited. A possible exception may be seen in cases of tardive dystonia, for which there is increasing evidence6 for the effectiveness of DBS. This remains an off-label use of DBS.

Realistic expectations

An important aspect of the multidisciplinary evaluation includes a discussion of the expectations for surgery, the risks, and the requirements for postoperative care. As discussed above, DBS is reversible and adjustable, so outcomes depend not only on accurate implantation of the hardware but also on postoperative programming. Also, monitoring and maintenance of the implanted hardware are required in these patients. It is important that patients and families appreciate the fact that specialized, long-term postoperative follow-up is as much a part of the treatment as is the implantation itself.

UNILATERAL VERSUS BILATERAL DBS

Most patients with generalized dystonia undergo bilateral DBS. However, patients with PD or essential tremor may receive bilateral, staged, or unilateral implants. Some patients with PD present with either near-complete predominance of symptoms on one side or with symptoms that affect mostly the dominant extremity. In these patients, unilateral implantation is often recommended because it has less risk than the bilateral approach and may be sufficient to address the most limiting symptoms.

As the disease advances, an additional surgery may be required to accomplish bilateral symptom control. Nevertheless, we do not routinely recommend preventive implantation because it is not known whether second-side symptoms will become severe enough to require it. This strategy allows for deferring surgical risk, which is in itself advantageous. In our experience, bilateral implantation is often recommended to PD patients who present with symptoms such as freezing of gait.

Patients who have essential tremor often present with bilateral symptoms. Although many patients will indicate that they need symptom relief on both upper extremities in order to perform activities of daily living, our practice is to recommend surgery on one side at first and to suggest the patient consider contralateral implantation after weeks or months. Bilateral implantation may carry a risk for dysarthria and the risk is thought to be reduced if bilateral procedures are staged. Although high rates of dysarthria have been reported following bilateral surgery for tremor, its occurrence has been infrequent in our experience with bilateral staged DBS. Benefits of treating tremor in the dominant extremity usually exceed those of treating nondominant tremor, so most patients prefer that the dominant side be the first one treated.

TECHNICAL OPTIONS

There are several technical options for implantation of DBS systems. Stereotactic procedures rely on co-registration of preoperative imaging with external and internal fiducials, or points of reference. Targeting of the intended structures is performed by combining direct and indirect methods. Direct methods rely on identification of the target structures with imaging, such as visualization of the STN and GPi on preoperative magnetic resonance imaging (MRI). Indirect targeting relies on cadaveric anatomic atlases and coordinate systems that infer the location of the intended structures in relation to anatomical points of reference.

Frame-based systems

Figure 2. In a frame-based system, the stereotactic arc is attached to the base of the frame. Entry points of the leads are marked on the skin and on the skull.
In the most common approach to DBS surgery,7 stereotactic frames are placed over the patient’s head and secured with pins. The frame becomes the fixed point of reference for accurate stereotactic surgery and must remain in place for the duration of the procedure. Computed tomography or MRI is then performed with the frame in place, so that the images are co-registered with the fiducial points of the stereotactic frame. The targets are then selected for surgery and trajectories are chosen based on anatomic structures. The patient is positioned supine and the frame and head are secured to the operating table. The coordinates calculated by the clinical workstations are then set to the stereotactic frame and arc. The stereotactic arc (Figure 2) is attached to the base of the frame and the entry points of the leads—where the burr hole will be placed—are marked on the skin and then on the skull. Once the burr hole and opening of the meninges are completed, the targeting cannulae are inserted. The microelectrode system is then mounted for recording of the target area and subsequently for final lead implantation.

Frameless systems

Figure 3. Surgeon’s view of the frameless device, placed over the head approximately at the level of the coronal suture. The occipital area is in the bottom of the figure. When a frameless system is used, a lighter-weight structure is affixed to the head.
The workflow and overall surgical procedure for implantation of DBS with frameless systems are similar to those of the frame-based procedure. However, instead of fixing the head to a rigid frame that prevents head motion, a lighter-weight, frameless system is fixed to the head and moves with it (Figure 3). First, metal screws and fiducials are fixed to the head under local anesthesia or sedation. Preoperative imaging is then acquired with the fiducials in place and the surgical plans are completed in the same fashion as for frame-based surgery. The patient is then placed supine on the operating table and the frameless system is attached to the head with the aid of image guidance, in the location determined by target and trajectory planning.

The key advantage of the frameless system over the frame-based system is greater mobility of the head. Another important advantage is easier access to the airway, should an emergency situation occur. In our practice, patients with experience of both frameless and frame-based systems did not report significantly less discomfort with the frameless system.

The frameless system also has disadvantages, including less secure fixation of the head, which can add risk to the procedure. In addition, because of its lightweight, plastic construction, it provides less robust support to the instrumentation entering the brain than do metallic head frames and, in some cases, there is less flexibility for adjusting targets if needed during surgery. In addition, frameless systems are nonreusable and represent a substantial additional cost.

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