Multimodal neurosurgical strategies for the management of dystonias

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Department of Neurosurgery, Neurological Institute, Tokyo Women's Medical University, Tokyo, Japan

Summary

Dystonia have many subtypes, and is classified as focal, segmental and generalized. As for focal dystonia, spasmodic torticollis (cervical dystonia) and writer's cramp are most common. Cervical dystonia is mainly treated effectively with selective peripheral denervation, and task specific focal dystonia of the hand (writer's cramp) is effectively alleviated by stereotactic ventro-oral thalamotomy. Generalized dystonia is dramatically improved with deep brain stimulation of the globus pallidus interna. Because the majority of dystonia is medically refractory and surgical treatment results in marked improvement, the authors strongly believe that dystonia should be regarded as a definite neurosurgical indication. Based on personal experience of nearly 200 cases of dystonia surgery, the authors describe a multimodal approach to various types of dystonias. Also we discuss possible relation between dystonias and psychiatric conditions, and future new indication of dystonia surgery.

Keywords: Dystonia; torticollis; writer's cramp; peripheral denervation; thalamotomy; deep brain stimulation.

Introduction

The term "dystonia" is used both as a name of disorder and a specific symptom. The range of symptoms is very wide and whether the underlying pathophysiology of various types of dystonia is uniform or not is not well known. In neurosurgical clinical practice, it is convenient to classify dystonias into pure cervical dystonia, task-specific focal hand dystonia, segmental and generalized dystonia. Because symptoms, signs, etiology, age, and so on differ greatly from patient to patient, we have to face various types of treatment modalities. We would like to introduce our consecutive experience of surgical management of these different types of dystonias.

Segmental and generalized dystonia

For segmental and generalized dystonia, the treatment of choice at present is bilateral globus pallidum interna (GPi) deep brain stimulation as in most other centers.

When I started pallidal surgery for dystonia about six years ago, the electrical stimulation devices were not readily available. Therefore, I used to perform sequential bilateral pallidotomy, and then I moved unilateral pallid-otomy (right side) and contralateral (left side) pallidal DBS. However, since 3 years ago, it has become our routine to implant bilateral pallidal DBS for generalized and segmental dystonia. Our method does not differ from those of other centers; MRI/CT fusion stereotaxi. Initially we used intravenous propofol sedation to control intraoperatively unnecessary movements and found that the dystonia symptoms worsened in some patients with light propofol anesthesia [2, 10]. We then found several reports that dystonia is induced by propofol anesthesia, and since then we have been using intravenous dexmedetomidine hydrochloride that is generally used for sedation in the intensive care unit.

In Japan, DYT-1 dystonia is not common because of genetic and racial factors, and the majority of our cases are adult onset idiopathic dystonia without family history. Some of them had a history of psychiatric problems treated with antipsychotic medication, and the symptoms may be classified as tardive dyskinesia, but response to pallidal DBS is generally the same as those without such a psychiatric history. We also experienced some cases of dystonias due to hereditary metabolic disorders such as Lesch-Nyhan syndrome and Hallervorden-Spatz syndrome with favorable results [9].

Although it is evident that the optimal target for dys-tonia lies in the GPi, it is not known whether the traditional GPi target used for control of Parkinson's disease (PD) is best for dystonia. Also many of the patients with dystonia tend to be obsessive or in an excessive anxiety state, which indicates that the background pathophysiol-ogy of dystonia also involves limbic pallidum that is anterior to the GPi target for control of motor symptoms. To explore a better stimulation area and to find any psychological changes with DBS in the more anterior pallidum, we usually implant two DBS electrodes on one side, resulting in four electrodes implanted in the brain. The posterior electrode is in the traditional GPi for PD, and the anterior electrode is placed 3 mm anteriorly. We generally externalized the lead and perform trial stimulation over three weeks to find the best motor effect and to see psychological changes. The details of this investigation will be published in the near future. After GPi stimulation, involuntary dystonic movements improve within hours, but abnormal fixed postures of the trunk, neck, and extremities tend to respond much later.

The indication or the role of GPi DBS for cervical dystonias (CD) has not yet been established [4]. However, based on our experience of 132 CD patients treated with selective peripheral denervation, we strongly believe that GPi DBS is definitely indicated in the complex type of CD. Complex type of CD is characterized by irregular involuntary head and neck movements and diffuse bilateral involvement of the neck muscles.

Cervical dystonia

Neurosurgical treatment of CD has a long history. In the beginning, the sternocleidomastoid muscle (SCM) and the accessory nerve were the target of surgical intervention. Then the importance of the posterior neck muscles, mainly the splenius muscle (SPL), was recognized. In order to denervate the accessory and cervical spinal nerves innervating to SCM and SPL, intradural rhizotomy was started, with some benefit. But inadequate denervation of SPL and complications due to denervation of normal muscles, turned out to be a problem. Some performed spinal cord stimulation to mimic sensory trick phenomenon. Bertrand [1] started and established selective peripheral denervation in which selective and complete denervation of the posterior neck muscles was accomplished by denervating the extradural dorsal rami of C1-C6 spinal nerves. This is now regarded as the safest and most effective neurosurgical treatment for the majority of CD. We modified this procedure to further minimize the side effects [6]. It is important to remember that the levator scapulae muscle is also involved in some CD patients resulting in lateral tilt of the head and elevation of the shoulder. In such cases, selective dener-vation of the levator scapulae muscle is safely performed [8]. Although peripheral denervation is a symptomatic treatment, many of the patients can enjoy symptom free life afterwards as if background pathophysiology was completely cured. As mentioned previously, in some complex type of CD and CD with extracervical symptoms, our preference is GPi DBS.

Task-specific focal hand dystonia

The most common type of task-specific focal hand dystonia is writer's cramp and musician's cramp. Such condition is very miserable, especially when the symptom is related with the patient's profession. As there have been some case reports on thalamotomy for writer's cramp, we started ventrooral thalamotomy for task-specific focal hand dystonia about five years ago [7]. This was because botulinum toxin injection is not approved in Japan for symptoms other than neck and face dystonias. The ventrooral nucleus of the thalamus receives inputs from GPi and forms part of the thalamo-cortical-basal ganglia loop. Task-specific focal hand dystonia is regarded as the result of oscillation of this cerebral circuit, and making a small lesion in this loop to de-sensitize the loop is the theoretical background of this treatment. So far we have treated 22 patients with writer's cramp and four with musician's cramp. Immediately after the operation, the effect is generally dramatic, but the problem is that recurrence rate is about 15% of patients. Such recurrence seems to be due to inadequate lesioning, because true lesioning and temporary thermal effect are difficult to distinguish during surgery. However, it is evident from our experience that we can cure writer's cramp and musician's cramp with ventrooral thalamotomy with minimal risk. There have been no permanent complications, though transient (2-3 weeks) mild limb weakness and dysarthria were seen in a few patients. One may argue why we do not perform DBS instead of lesioning. This is of course debatable, but the main reason is that DBS merely leads to suppression of the symptom, but thalamotomy can result in permanent cure. DBS itself has disadvantages in terms of hardware complications and psychological burden on the patients; they are living with a device and the disease itself is not cured. Patients with focal hand dystonia are generally young (32 years old on average in our series), and the risk of thalamotomy is supposed to be lower than in aged population as in PD patients. Recovery from complications, if any, is considered faster and more complete.

Recently we found task-specific focal ''foot'' dystonias among semi-professional speed skaters. The symptom appears only when they skate, and the foot moves at the ankle joint laterally like valgus. This condition is well-known among Olympic level skaters in Japan and they call it Burabura (floppy) disease in slang.

Issue on dystonia and psychiatric conditions

It is well known that patients with dystonia tend to have a particular psychological or mental character. Patients with CD are often depressive, aggressive, but occasionally obedient. Focal hand dystonia patients are often obsessive, and perfect and impeccable pursuit. Those with DYT-1 dystonia are almost always bright, clever, intelligent. Patients with dystonias may develop psychiatric problems even after treatment of the physical symptoms, and it is also well known that psychiatric disorders are sometimes followed by movement disorders called tardive dyskinesia and dystonia. Thus movement disorders, especially dystonia, seem to be closely related with psychiatric or mental conditions. Dystonia is regarded as an expression of dysfunction of the tha-lamo-cortical-basal ganglia motor loop, but there are many other loop circuits in the brain and dysfunction of some of these loops are responsible for psychiatric disorders such as depression and obsessive disorders. The motor and mental functions of the brain are basically the output (efferent) system. Therefore, as there are many motor disorders as shown in Table 1, there must be corresponding psychiatric disorders such as mental tremor, mental dystonia, mental spasticity, mental dyskine-sia, and so on. We assume these conditions are generally and traditionally called psychiatric disorders such as depression, obsession, compulsion, anxiety, and so on. Therefore, it is reasonable that surgical treatment of in-

Table 1

Motor

Possible mental

Traditional mental and

symptoms

symptoms

psychiatric symptoms

Tremor

mental tremor

depression

Ataxia

mental ataxia

obsession

Dystonia

mental dystonia

compulsion

Chorea

mental chorea

anxiety

Ballism

mental ballism

mania

Dysmetry

mental dysmetry

schizophrenia

Spasticity

mental spasticity

personality disorder

Apraxia

mental apraxia

mental retardation

Palsy

mental palsy

etc

etc

etc

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