Essential Tremor

Surgical Management

For patients with severe, disabling, medication-refractory tremor, a surgical approach may be considered. Interruption of ventralis intermedius thalamic output to the motor cortex has demonstrated efficacy in eliminating several tremor types. In addition, advances in neuroimaging and stereotactic techniques have enabled the performance of such procedures with improved accuracy and lower surgical morbidity than in the past. Major contraindications for surgical management of ET include marked cognitive problems or unstable medical diagnoses that may significantly increase surgical risk.

Surgical management of ET includes ablative therapy through stereotactic thalamotomy or chronic thalamic deep brain stimulation (DBS).

Stereotactic thalamotomy
Surgical procedures have been used to treat ET since the 1950s. Over time, the optimal target for surgical ablation was determined to be the ventralis intermedius (VIM) nucleus of the thalamus. Current theories suggest that efficacy of VIM thalamic lesions for tremor may be explained by connectivity of the basal ganglia-thalamocortical motor loop, a pathway of which is proposed to consist of fibers from the contralateral dentate nucleus of the cerebellum through the posterior ventralis lateralis thalamic nucleus to the motor cortex.

The first published reports concerning thalamotomy in ET indicated that more than 90% of patients demonstrated contralateral improvement. Although most of these assessments were performed before standardized tremor clinical rating scales were developed, reported studies and current clinical observations indicate the efficacy of unilateral thalamotomy. The percentage of ET patients who experience tremor remission and concomitant functional improvement following thalamotomy has been reported to range from approximately 78% up to 100%. In addition, long-term follow-up studies report that the benefits of stereotactic thalamotomy continue in most patients. However, tremor may recur in 20% to 30% of patients.

In addition, the procedure has potential complications, particularly when performed bilaterally. Such complications may include dysarthria, intractable paresthesias, confusion, attention deficits, contralateral hemiparesis, and visual field defects. Reports of complication rates vary from 1% to 20%. Bilateral thalamotomies usually are avoided due to a high risk of severe, persistent dysarthria or other potential complications.

Deep brain stimulation (DBS)
Thalamic stimulation mimics the effects of surgical lesioning while allowing for adjustments to maximize efficacy. During the early to mid 1960s, a number of investigators reported tremor ablation through high frequency, intraoperative stimulation of the VIM thalamic nucleus. Improvements in tremor scores range widely, but 50% improvement is common. The potential side effects, many of which are transient, include paresthesia, dysarthria, dysequilibrium, and paresis.

A comparison of thalamotomy and thalamic DBS in age-, sex-, and severity-matched ET patients indicated that both procedures reduced tremor by approximately 50% at 2 to 3 months post-operation. Thalamotomy caused more serious acute complications, including hemorrhage, cognitive changes, and hemiparesis, while DBS caused more long-term complications related to hardware malfunction. The authors considered DBS to be "clinically superior" based on the comparison.

R Pahwa, KE Lyons, SB Wilkinson, AI Troster, J Overman, J Kieltyka, WC Koller. Comparison of thalamotomy to deep brain stimulation of the thalamus in essential tremor. Movement Disorders 2001;16:140-143

DBS has been available since 1995 in Europe, Canada, and Australia. In 1997, the United States Food and Drug Administration approved unilateral (one-sided) thalamic stimulation (using a system from Medtronic®) for control of tremor in ET. It has since gained acceptance as an alternative to surgical ablation of the VIM thalamic nucleus, and in many centers is now the preferred procedure.

During thalamic DBS, electrodes are implanted in the VIM nucleus of the thalamus. In addition, a device known as an implantable pulse generator (IPG) is placed subcutaneously in the subclavicular region. After appropriate postoperative testing, leads from the implanted electrodes are connected to the pulse generator, which then delivers continuous high frequency electrical stimulation to the thalamus. The IPG may be turned off by passing a hand-held magnet over the device. An external programming device is used to program adjustable variables, including selection of stimulating contacts, pulse width, amplitude, and frequency. For patients who experience paresthesia, dyarthria, or other symptoms in association with DBS, adjustment of stimulator settings may often minimize these effects.

In general, the results of DBS are equal to or better than those reported in patients with ET who have had a thalamotomy and thalamic stimulation is believed to be a safe and effective means of treating ET in selected patients. However, in some patients, tremor may not be eliminated and may continue to cause some degree of impairment. (For a listing of the advantages and disadvantages of DBS, please refer to table 8.)

Table 8. Advantages and Disadvantages of DBS
Advantages of DBS:	Disadvantages of DBS:
Nondestructive	Increased expense of the system
Reversible	Need for implantation of foreign material, causing potential risk of inflammatory responses and infection
Adaptable (ability to change impulse variables to minimize side effects, increase efficacy, and address late tremor recurrence seen in some patients)	Need to replace batteries and hardware
Associated with stimulation-related complications that are typically reversible	Time and effort required to optimize stimulation parameters
Ability to perform bilateral procedures with reduced risk of permanent morbidity

It is important to note that, as with any invasive procedure, there are surgical risks associated with both thalamotomy and DBS (e.g., stroke, hemorrhage, permanent speech impairment, etc.).