Patient Selection

Patients who are candidates for DBS are typically refractory to standard medical therapy that included multiple trials with varying dosages and combinations of pharmacotherapy. Once a diagnosis of PD is confirmed, expeditious medication trials are encouraged, in order that years of potential benefit from subsequent surgery are not lost if the patient eventually becomes a medication failure. Ideally the surgeon prefers to consider patients whose clinical severity has not progressed toward end stages where surgical intervention becomes less appropriate. However, in most centers, DBS and lesion placement for PD are performed as late as age 80 years. This is predicated on the patient still evidencing good results to preoperative neuropsychological testing that demonstrates no more than minimal signs of dementia. Similar criteria are applied when contemplating DBS treatment for tremor per se.

Dystonia, in contrast, typically involves children as young as ages 6–8 years. Although adequate genetic testing is helpful for diagnosis, many dystonia patients are DYT-1 negative. The presence or absence of genetic confirmation does not determine which child will benefit from DBS.

Decisions to pursue DBS for patients with variable clinical presentations, including severe essential tremor, PD, or dystonia, are clinical ones. Patients are initially selected from those who have failed various medication protocols. The neurosurgeon then considers the potential contribution of the invasive procedure to the patient’s overall quality of life as well as its potential acute and chronic side effects and thus its relative risk benefits.

General Procedure

The operations are performed stereotactically, typically with the help of a frame affixed to the head of the patient (Fig. 43-1). This frame serves to create a space with x, y, and z coordinates that the head, and thus the brain, lies within. As such, any particular location within that space can be targeted using devices to place and hold a probe tip, recording electrode, or stimulating electrode at the desired coordinates. These systems are highly accurate, provided the surgeon is specifically trained and able to precisely focus the probe target within just 1 mm of an intended therapeutic site deep within the appropriate target brain structures including the basal ganglia, thalamus, or subthalamic brain structures. A system of stereotactic targeting software is used to define readily appreciated common brain structures as initial reference points. These systems typically use measurements based on the location of the anterior and posterior commissures.

Figure 43-1 Surgical Management of Movement Disorders.

During the intraoperative procedure, the patients are kept awake and monitored by a clinical neurophysiologist. As the probe is advanced, specific cell types are verified physiologically by having a clinical neurophysiologist make microelectrode recordings along the probe’s trajectory toward the intended subcortical target. Cells in certain specific areas have reproducible physiologic signatures vis-à-vis their firing rates and patterns. The utilization of these physiologic markers helps validate the exact location of the electrode (see Fig. 43-1).There are major albeit relatively uncommon risks associated with these procedures, the most significant being a debilitating or fatal intracerebral hemorrhage; currently, these complications still occur in approximately 0.5–3% of cases.

Operations Performed For Movement Disorders