Deep brain stimulation of the globus pallidus internus (GPI) for torsion dystonia--a report of two cases

Convergent mechanisms in etiologically-diverse dystonias

INTRODUCTION

Dystonia is a neurological disorder associated with twisting motions and abnormal postures, which compromise normal movements and can be both painful and debilitating. It can affect a single body part (focal), several contiguous regions (segmental), or the entire body (generalized), and can arise as a result of numerous causes, both genetic and acquired. Despite the diversity of causes and manifestations, shared clinical features suggest that common mechanisms of pathogenesis may underlie many dystonias.

AREAS COVERED

Shared themes in etiologically-diverse dystonias exist at several biological levels. At the cellular level, abnormalities in the dopaminergic system, mitochondrial function and calcium regulation are often present. At the anatomical level, the basal ganglia and the cerebellum are frequently implicated. Global CNS dysfunction, specifically aberrant neuronal plasticity, inhibition and sensorimotor integration, are also observed in a number of dystonias. Using clinical data and data from animal models, this article seeks to highlight shared pathways that may be critical in understanding mechanisms and identifying novel therapeutic strategies in dystonia.

EXPERT OPINION

Identifying shared features of pathogenesis can provide insight into the biological processes that underlie etiologically diverse dystonias, and can suggest novel targets for therapeutic intervention that may be effective in a broad group of affected individuals.

Treatment strategies for dystonia

IMPORTANCE OF THE FIELD

Dystonia is a neurological syndrome characterized by involuntary twisting movements and unnatural postures. It has many different manifestations and causes, and many different treatment options are available. These options include physical and occupational therapy, oral medications, intramuscular injection of botulinum toxins, and neurosurgical interventions.

AREAS COVERED IN THIS REVIEW

In this review, we first summarize the treatment options available, then we provide suggestions from our own experience for how these can be applied in different types of dystonia. In preparing this review article, an extensive literature search was undertaken using PubMed. Only selected references from 1970 to 2008 are cited.

WHAT THE READER WILL GAIN

This review is intended to provide the clinician with a practical guide to the treatment of dystonia.

TAKE HOME MESSAGE

Treatment of dystonia begins with proper diagnosis and classification, followed by an appropriate search for underlying etiology, and an assessment of the functional impairment associated with the dystonia. The therapeutic approach, which is usually limited to symptomatic therapy, must then be tailored to the individual needs of the patient.

Treatment of dystonia with deep brain stimulation

Pallidal deep brain stimulation (DBS) is an established treatment option for medically refractive dystonia. The mechanism by which globus pallidus pars interna (GPi) DBS improves dystonia is still unclear. Primary generalized dystonia usually responds well to this therapy, as recently confirmed in two well-designed, double-blind, controlled trials; however, predictors of outcome within this population are not well known. The role of GPi DBS in idiopathic cervical dystonia resistant to treatment with botulinum toxin, in tardive dystonia, and in some types of secondary dystonia are emerging as populations of patients who may also benefit, but outcomes are not well documented. Serious complications from this therapy are rare. Future research will likely continue to address the most appropriate programming settings for various populations of dystonia, the mechanism by which DBS affects dystonia, and the possibility of alternative brain targets that might have less associated side effects or greater efficacy than the GPi.

Bilateral deep-brain stimulation of the globus pallidus in primary generalized dystonia

BACKGROUND

Severe forms of dystonia respond poorly to medical treatment. Deep-brain stimulation is a reversible neurosurgical procedure that has been used for the treatment of dystonia, but assessment of its efficacy has been limited to open studies.

METHODS

We performed a prospective, controlled, multicenter study assessing the efficacy and safety of bilateral pallidal stimulation in 22 patients with primary generalized dystonia. The severity of dystonia was evaluated before surgery and 3, 6, and 12 months postoperatively during neurostimulation, with the use of the movement and disability subscores of the Burke-Fahn-Marsden Dystonia Scale (range, 0 to 120 and 0 to 30, respectively, with higher scores indicating greater impairment). Movement scores were assessed by a review of videotaped sessions performed by an observer who was unaware of treatment status. At three months, patients underwent a double-blind evaluation in the presence and absence of neurostimulation. We also assessed the patients' quality of life, cognition, and mood at baseline and 12 months.

RESULTS

The dystonia movement score improved from a mean (+/-SD) of 46.3+/-21.3 before surgery to 21.0+/-14.1 at 12 months (P<0.001). The disability score improved from 11.6+/-5.5 before surgery to 6.5+/-4.9 at 12 months (P<0.001). General health and physical functioning were significantly improved at month 12; there were no significant changes in measures of mood and cognition. At the three-month evaluation, dystonia movement scores were significantly better with neurostimulation than without neurostimulation (24.6+/-17.7 vs. 34.6+/-12.3, P<0.001). There were five adverse events (in three patients); all resolved without permanent sequelae.

CONCLUSIONS

These findings support the efficacy and safety of the use of bilateral stimulation of the internal globus pallidus in selected patients with primary generalized dystonia.

Stimulation of the globus pallidus internus for childhood-onset dystonia

We report the results of deep brain stimulation (DBS) of the globus pallidus internus (GPi) in 12 patients with childhood-onset generalized dystonia refractory to medication, including 3 patients with status dystonicus. There were 8 patients who had DYT1-negative primary dystonia, 1 had DYT1-positive dystonia, and 3 had symptomatic dystonia. Stimulation was effective in all but 1 patient. Dystonic postures and movements of the axis and limbs responded to DBS to a greater extent than oromandibular dystonia and fixed dystonic postures. These findings provide further evidence that pallidal stimulation is an effective treatment for intractable childhood-onset dystonia, including status dystonicus, and together with previous findings, suggest that it should be considered the treatment of choice for these conditions.

What's in a "smile?" Intra-operative observations of contralateral smiles induced by deep brain stimulation

OBJECTIVE

To describe smiling and euphoria induced by deep brain stimulation (DBS).

BACKGROUND AND SIGNIFICANCE

The brain systems inducing emotional experiences and displays are not entirely known, but the ventral striatum including the nucleus accumbens has been posited to play a critical role in mediating emotions with positive valence. DBS has been successfully employed for the treatment of movement disorders, and most recently obsessive compulsive disorder (OCD). The purpose of this report is to describe the emotional changes associated with stimulation of the ventral striatum.

METHODS

A single patient with intractable OCD had electrode arrays placed in the right and left anterior limbs of the internal capsule and region of the nucleus accumbens. Changes in facial movement during stimulation were quantified by video recording. Ten video segments, time locked to the onset of stimulation, were digitized and changes in pixel intensity that occurred over both sides of the lower face, on a frame by frame basis, following stimulation onset were computed. These summed changes in pixel intensity represented the dependent variable of "entropy" and directly corresponded to changes in light reflectance that occur during facial movement.

RESULTS

During stimulation on both the right and left side, the patient consistently developed a half smile on the side of the face contralateral to the stimulating electrode, and also became euphoric. The effect ceased when DBS was discontinued.

CONCLUSIONS

DBS in the region of the nucleus accumbens produced smile and euphoria suggesting that alterations in the ventral striatum may result in emotional experience and displays. We hypothesize the existence of a limbic-motor network responsible for such changes. This observation suggests that DBS may be useful as a therapy for mood disorders.

Effect of deep brain stimulation of GPI on neuronal activity of the thalamic nucleus ventralis oralis in a dystonic patient

OBJECTIVE

To record the possible effect of acute deep brain stimulation (DBS) of the globus pallidus internus (GPI) on the neuronal activity of the ventralis oralis anterior (VOA) nucleus of the thalamus.

METHODS

Under general propofol anaesthesia, extracelullar single unit recordings were performed in VOA of a post-anoxic dystonic patient previously implanted with GPI located electrodes for chronic DBS.

RESULTS

Neurons recorded in the VOA could be classified in two cell subpopulations: a high firing rate (16.5 Hz) and low burst index (BI; 15.6) type and a low firing rate (5.5 Hz) and high BI (35.6) type. GPI electrical stimulation reduced the frequency and increased the BI of the high firing rate cells while leaving the other cell type unchanged.

CONCLUSION

These results demonstrate that pallidal DBS is able to inhibit a subpopulation of motor thalamic cells and question the pathophysiological model of dystonia based on a low firing rate of GPI cells.