Outcomes from stereotactic surgery for essential tremor

Abstract

There are several different surgical procedures that are used to treat essential tremor (ET), including deep brain stimulation (DBS) and thalamotomy procedures with radiofrequency (RF), radiosurgery (RS) and most recently, focused ultrasound (FUS). Choosing a surgical treatment requires a careful presentation and discussion of the benefits and drawbacks of each. We conducted a literature review to compare the attributes and make an appraisal of these various procedures. DBS was the most commonly reported treatment for ET. One-year tremor reductions ranged from 53% to 63% with unilateral Vim DBS. Similar improvements were demonstrated with RF (range, 74%-90%), RS (range, 48%-63%) and FUS thalamotomy (range, 35%-75%). Overall, bilateral Vim DBS demonstrated more improvement in tremor reduction since both upper extremities were treated (range, 66%-78%). Several studies show continued beneficial effects from DBS up to five years. Long-term follow-up data also support RF and gamma knife radiosurgical thalamotomy treatments. Quality of life measures were similarly improved among patients who received all treatments. Paraesthesias, dysarthria and ataxia were commonly reported adverse effects in all treatment modalities and were more common with bilateral DBS surgery. Many of the neurological complications were transient and resolved after surgery. DBS surgery had the added benefit of programming adjustments to minimise stimulation-related complications. Permanent neurological complications were most commonly reported for RF thalamotomy. Thalamic DBS is an effective, safe treatment with a long history. For patients who are medically unfit or reluctant to undergo DBS, several thalamic lesioning methods have parallel benefits to unilateral DBS surgery. Each of these surgical modalities has its own nuance for treatment and patient selection. These factors should be carefully considered by both neurosurgeons and patients when selecting an appropriate treatment for ET.

Keywords: electrical stimulation; stereotaxic surgery; tremor; ultrasound.

Figure 1

Diagram of dentatorubrothalamic tract. Fibres arising from the contralateral dentate and interposed cerebellar nuclei project superiorly through the superior cerebellar peduncle. Some fibres synapse in the magnocellular portion of the red nucleus before continuing to the thalamus (rubrothalamic tract) and some fibres continue to the ventrolateral thalamus (dentatothalamic tract). These fibres synapse in a somatotopic fashion in the ventral intermediate thalamic nucleus, Vim. From the Vim, thalamocortical fibres pass through the superior thalamic radiation to the motor and premotor cortex (Brodman’s Area 4 and 6).

Figure 2

Surgical treatment recommendations for essential tremor. (A) For patients with predominant unilateral tremor symptoms; contralateral DBS or thalamotomy with RF, FUS or GKRS are all surgical options. For eligible patients with bilateral tremor symptoms who wish to have both upper extremities treated, bilateral DBS can be performed safely. Bilateral thalamic DBS can be offered in a single operation, in a staged fashion or in a delayed staged fashion (months or years after initial surgery). For patients who received unilateral DBS and whose contralateral symptoms progress or become disabling, staged contralateral DBS is an option. Among patients received unilateral DBS but who do not want to undergo secondary DBS surgery, RF or GKRS thalamotomy procedures can be performed. For patients who have had infections or do not want additional implanted devices RF thalamotomy is a good option. For patients who are elderly, who are taking anticoagulants or who have general medical conditions that do not permit open surgical procedures, GKRS thalamotomy is a good treatment option. (B) Among patients who refuse DBS treatment for ET, patients with poor medical condition may be eligible for GKRS thalamotomy. For patients with favourable ultrasound penetrating skull characteristics, FUS thalamotomy is an option, and for patients with prior infected DBS systems, RF thalamotomy can be performed. ET, essential tremor; DBS, deep brain stimulation; FUS, focused ultrasound; GKRS, gamma knife radiosurgical; RF, radiofrequency.