Paul
C. Francel, M.D., PH.D.
David Coffman, M.D.
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INTRODUCTION
Parkinson's disease (PD), essential tremor, and other diseases
associated with either tremor or other movement disorders can be
treated effectively using stereotactic neurosurgical techniques.
Surgical treatment for many of these movement disorders began in
the early l950s with pioneering work by Leksell in the treatment
of PD with pallidotomy. These early surgeries targeted the
anterodorsal portion of the globus pallidus and yielded
significant improvement although not with the same success rate
as has been seen recently. A better understanding of the
functional organization of the basal ganglia based on
neurophysiological studies and basic science research has helped
researchers to discover other potential stereotactic brain
targets for the treatment of various movement disorders beyond
the globus pallidus.
The treatment of movement disorders, particularly PD, changed in the late l960s with the discovery of levodopa (L-dopa). Its advent suggested to physicians that there may be a potential cure or "magic bullet" for the treatment of intractable PD. Its utility was completely logical based on the biochemical pathways as understood at that time for the production of dopamine in the neostriatum: L-dopa would act as a precursor, obviating the metabolism of tyrosine to subsequent metabolites, so that only dopa-decarboxylase would be required to convert the L-dopa to dopamine. The dopamine created could subsequently be used to replace the diminishing dopamine supply occurring in patients with PD. Further anatomic studies revealed that the source of these cells was in the substantia nigra and that they projected to the nuclei of the neostriatum, where they subsequently exerted an inhibitory influence.
Clinical management has since revealed that this medical management is incomplete, stirring the pharmaceutical industry to create additional drugs for the treatment of PD and other movement disorders. New dopamine agonists and other pharmaceuticals have become available and appear useful in the treatment of PD. However, patients currently with PD tend to be elderly, presenting with more advanced disease, and appear to suffer from side effects of their medication after several years of usage, particularly with L-dopa (Sinemet).
Prior to the current stereotactic approach to the treatment of movement disorders, there was interest in surgical transplantation, particularly transplantation with adrenal medullary tissue. Unfortunately, this has shown only modest results. Fetal cell transplantation has potential promise; however, there are major drawbacks and in particular, medical, social, and ethical disadvantages. The stereotactic treatment of movement disorders is demonstrating excellent results in the symptomatic management of movement disorders and will be discussed in detail below. In the United States alone, there are more than one million parkinsonian patients and an even greater number of patients with essential tremor and other movement disorders. These patients require aggressive treatment in order to regain their quality of life.
The initial return to surgical treatment occurred secondary to an improved understanding of the physiological circuits within the basal ganglia itself. It has become clear that the globus pallidus plays an integral role as the outflow tract from the striatal pallidal circuitry, which subsequently particularly affected circuitry with the thalamus and the motor cortex. Initial work done in the 1950s targeted the anterodorsal portion of the globus pallidus, but as further electrophysiological understanding of the circuitry was elucidated, the target for this pallidotomy slowly moved toward the ventral posterior and lateral portions of the globus pallidus interna. This targeting has been further improved using new applications of stereotactic technology and improvements with computer software imaging and intraoperative monitoring.
This chapter describes the system that we use for imaging and the surgical treatment of these patients. Using stereotactic technology, multiple special imaging sequences, and computer software, we have been able to stereotactically lesion or to stereotactically place deep brain stimulation (DBS) electrodes with high accuracy and minimal morbidity.
Such systems have also enabled a significant shortening in operative time, along with improved patient comfort and safety. The selection of qualified patients, however, is critical to the process, as is the selection of the appropriate procedure.
PATIENT SELECTION
The specific surgical treatment varies with each patient and is
based on the most prominent movement disorder. Much of the
discussion here applies to patients with PD, which is the most
common group of patients treated. A subsection describes the
selection of patients with essential tremor. It is these authors'
expectation, as well as many others, that additional movement
disorders (such as dystonia and cerebellar tremor) will be
amenable to using similar techniques. The discussion here will
convey the concepts best in terms of surgical management.
PD is a progressive disorder characterized by cog-wheel rigidity, bradykinesia/akinesia, and/or resting tremor. Some patients suffer from additional symptoms including superimposed dystonia and occasional muscle pain. The initial diagnosis of these symptoms as PD and the initiation of dopaminergic medication such as L-dopa appear to provide significant improvement for patients and, in fact, is part of the diagnostic criteria for describing a disorder as PD as opposed to other Parkinson's plus diseases such as multisystem atrophy or Shy-Drager syndrome. In the latter, there is little or no response to L-dopa, and other symptoms or signs may be present showing evidence of a multifocal or diffuse neurodegenerative disease. Presently, these patients are not candidates for the currently used surgical procedures involving lesioning or stimulation of the globus pallidus, the ventral interomedial (Vim) nucleus of the thalamus, and/or the subthalamic nucleus.
After taking dopaminergic medications for several years, many PD patients begin to develop severe drug-induced dyskinesias or even psychotic reactions that limit the use of their medications. Over time, these medications become less effective in controlling Parkinson's symptoms and dosage often becomes the critical issue because of the narrow difference between effective medication dosage, under-treatment of the disease, and toxic and/or intolerable side effects.
Initially, the operative procedures for stereotactic lesioning were thalamotomy and pallidotomy. Stereotactic thalamotomy has been found to be extremely effective in control of tremor. However, in a patient with PD in which other symptoms may be present, thalamotomy alone appears to be ineffective and addresses only the tremor. This provided the resurgence of stereotactic pallidotomy, which has become the gold standard surgical treatment for PD when medical therapy falls. The pallidotomy itself is not a curative procedure, and the patient must realize that pallidotomy does not stop the disease progression. In several series, pallidotomy has been found to be most effective for the treatment of disabling dyskinesias and, occasionally, improvement in dyskinesia occurs on the ipsilateral side as well. Pallidotomy clearly can help contralateral rigidity, bradykinesia, dystonia, tremor, and freezing. Improvement in walking is difficult to predict preoperatively since some patients show a marked improvement in their walking if the unilateral pallidotomy has bilateral beneficial effects; if the effect is mainly unilateral, no improvement in gait may be seen. Since walking is a complex bilateral motor activity, it may not be tremendously affected. Bilateral pallidotomies in this elderly population are not recommended because of the likelihood of hypophonia, dysarthria, and swallowing difficulties. Pallidotomy may also occasionally help patients with freezing episodes and limit the abruptness of on/off fluctuations. There is little evidence that pallidotomy helps with akinesia or any depressive components of PD, especially in individuals with associated multiinfarct dementia. For this reason, a patient showing evidence of significant dementia is not a candidate for the procedure.
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© 2000 The American Association of Neurological
Surgeons
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