Leksell's posteroventral pallidotomy in the treatment of Parkinson's disease

Identification and localization of intracerebral vessels by microvascular doppler in stereotactic pallidotomy and thalamotomy: technical note

OBJECTIVE

To identify intracerebral vessels in proximity to the target for thermocoagulation in functional neurosurgery, we use a microvascular doppler sensor held in a special supporting needle that fits in the straightening cannula for the thermocoagulation needle.

TECHNIQUE

After insertion of the straightening cannula aimed at the stereotactic target, the microvascular doppler probe positioned at the tip of a supporting hollow needle is advanced through the cannula. The proximal micrometer gauge indicates the depth of the tip of the doppler probe. By setting the doppler device to the shortest focusing depth (0.1 mm), the maximum pulsatile vascular sound indicates the depth of the vessel.

RESULTS AND CONCLUSION

A prominent vascular sound was identified in 3 of 13 cases. By adjusting the depth of the target, no major bleeding was experienced after thermocoagulation lesions were made. This technique secures and protects the fragile microvascular doppler and identifies any significant arterial vessels at the stereotactic target, thus avoiding vascular injury.

Magnetic resonance image evaluation of pallidotomy lesions: a volumetric and shape analysis

Determination of acute pallidotomy-produced lesion volumes, pre- and postpallidotomy globus pallidus (GP) volumes, and assessment of lesion shape using magnetic resonance (MR) imaging-based computerized segmentation (contouring) and three-dimensional rendering was made in 19 patients. Magnetic resonance image slice thickness (1.5 mm or 6 mm) was not found to be a significant factor influencing contour-based pallidotomy lesion volume estimates. Previously reported lesion volumes produced by pallidotomy have often been estimated using the ellipsoid volume formula. Using 1.5-mm-thick MR sections, contour-based pallidotomy-produced lesion volumes were significantly different from those volumes estimated by the ellipsoid formula. Globus pallidus volumes, estimated by contouring T2-weighted MR images, were bilaterally similar (2.4 ± 0.37 ml [right]; 2.2 ± 0.45 ml [left]). Postoperative GP volumes were found on the contralateral, unlesioned side to be 2 ± 0.45 ml and on the lesioned side to be 1.25 ± 0.45 ml. Using the contralateral, unlesioned side as a reference volume, approximately 39 ± 14% of the GP was visibly affected on the lesioned side. Seventeen of 18 patients had a favorable outcome with reduced dyskinesias and "off" time with improvement in parkinsonian symptoms.

Analysis of computerized three-dimensional rendering of pallidotomy-produced lesions based on MR images showed no relationship between lesioning technique and resulting lesion shape. Important factors in the volumetric analysis of pallidotomy lesions are identified and allow reasonable assessment of the pallidotomy lesion volume and shape and the extent of the affected GP.

Pallidal and thalamic surgery for Parkinson's disease

With increasing understanding of the pathophysiology of movement disorders and the refinement of stereotactic techniques, interest in and the scope of surgical techniques for the management of Parkinson's disease have recently rapidly increased. With the option of chronic stimulation or lesion-making in a variety of brain sites, surgical treatment can be increasingly tailored to a particular patient's needs.

Usefulness of pallidotomy in advanced Parkinson's disease

OBJECTIVE

The combined effect of posteroventral pallidotomy and optimal medical treatment was assessed in 22 patients with levodopa sensitive Parkinson's disease.

METHODS

Timed motor tests, video recordings, and computer assisted optoelectronic movement analysis were used for serial hourly assessments performed preoperatively and four and 12 months after operation. Tests were made while patients were on optimal medical therapy.

RESULTS

There were no serious adverse events of surgery. Two of the 22 patients could not complete all the tests after operation. The proportion of dyskinesia periods decreased in the 20 patients and there was a proportional increase in normal or fairly normal occasions. "Off" periods were not significantly affected. In 12 of 13 patients with limb dyskinesia this symptom was completely abolished in the contralateral limbs. There was also some degree of improvement axially and ipsilaterally. Tremor was moderately improved contralaterally. Bradykinesia remained unchanged. Results at 12 months follow up were similar to those at four months.

CONCLUSION

Pallidotomy produced a pronounced positive effect on dyskinesia and a moderate effect on tremor. Bradykinesia was not affected. Posteroventral pallidotomy may be useful in patients with Parkinson's disease who have severe motor fluctuations and may allow an increase in levodopa dose to alleviate bradykinesia in "off" states.

Effects of graft-derived dopaminergic innervation on the target neurons of patch and matrix compartments of the striatum

Fetal dopaminergic neurons grafted into the dopamine-depleted striatum have previously been shown to normalize neurochemical and behavioural abnormalities. However, the extent of graft-induced recovery of striatal compartments, which differ in their ontogeny, neurochemical properties and function, is still not clear. The striosome and matrix compartments of the striatum provide a segregated projection to somatostatin-containing GABAergic neurons of the rostral part of the entopeduncular nucleus and somatostatin-negative GABAergic neurons of the caudal part of the entopeduncular nucleus, respectively. In the present study, preprosomatostatin and glutamate decarboxylase messenger RNA levels in the rostral and caudal parts of the entopeduncular nucleus were determined six and 18 months postgrafting in rats with complete recovery of rotational behaviour following apomorphine challenge, and in rats with unilateral 6-hydroxydopamine lesions or sham lesions and no grafts. Sections were processed for in situ hybridization using 35S-labelled cRNA probes for glutamate decarboxylase (67,000 mol. wt isoform; GAD67) and preprosomatostatin. Autoradiographs showed a marked increase in preprosomatostatin messenger RNA within the ipsilateral entopeduncular nucleus in 6-hydroxydopamine-lesioned rats, and a substantially lower increase six months postgrafting. At 18 months postgrafting, the preprosomatostatin messenger RNA levels were symmetrical within the entopeduncular nucleus. Unilateral depletion of striatal dopamine resulted in a moderate increase in GAD67 messenger RNA levels within the ipsilateral entopeduncular nucleus, along with a substantial decrease in GAD67 levels within the contralateral nucleus. By six months postgrafting, the GAD67 levels had decreased considerably within the ipsilateral entopeduncular nucleus, while the messenger RNA levels had returned to normal within the contralateral nucleus. Interestingly, at 18 months postgrafting, the GAD67 levels remained decreased within the ipsilateral entopeduncular nucleus and were significantly lower than the normal value. The results indicate that fetal nigral grafts placed within the dopamine-depleted striatum can restore the neurochemical alterations seen in striatal target areas such as the entopeduncular nucleus. This may form the neurochemical basis of graft-induced behavioural recovery, as the normalization of neurotransmitter messenger RNA levels in the entopeduncular nucleus reflects the restoration of overall activity in both direct and indirect striatal output pathways. The results also indicate that the graft-derived dopaminergic innervation restores the output of both striosome and matrix compartments of the striatum. The present results also showed a progressive recovery leading to over-compensation of neurotransmitter messenger RNA levels following grafting, perhaps indicating the importance of feedback regulation of grafted dopaminergic neurons by the host.

Highest level automatisms in the nervous system: a theory of functional principles underlying the highest forms of brain function

A concept that all hierarchical levels of the nervous system are built according to the same functional principles is proposed. Each level is responsible for a discrete type or set of automatisms, is a learning system, and contains two distinct functional subdivisions: (1) a controller, a subsystem providing a governing set of rules or commands-a control law-that directs the action of the recipient of these rules-the controlled object; and (2) a model, a subsystem that generates a model of object behavior, i.e. afferent information flow expected from the controlled object. A control system such as this receives two types of afferent signals-initiating and informational. The difference between these signals is that a control system minimizes initiating signals during the realization of an automatism, i.e. a control neural network utilizes informational signals to compute the proper output that minimizes the initiating input signal. A mismatch or error signal, a type of initiating signal, is responsible for learning. Both the control law and the model can be adjusted during learning. The learning process starts when the error signal increases and stops when it is minimized. A network hierarchy is structurally and functionally organized in such a way that a lower control system in the nervous system becomes the controlled object for a higher one. This hierarchy leads to a generalization of encoded functional parameters and, consequently, the working space for each higher level control system becomes more abstracted. This is the reason why each hierarchical level within the control nervous system uses detectors specific for feature of the controlled object and the environment that match the control needs in order to obtain information about the current state of the object in the environment. Movement of information toward higher hierarchical levels also is accompanied by an increase in the duration of initiating signals within each control system. The ability to store a long prehistory of preceding events is considered as the mechanism that necessitated the invention of more complex and more rapid forms of learning such as operant learning, and made possible more complex multistep computational algorithms that require memorization of the results of previous intermediate computations. The functions of the cerebellum, the limbic system and the cortico-basal ganglia-thalamocortical loops are analyzed to illustrate the utility and applicability of this theoretical concept. Basal ganglia-thalamocortical loops are described as modeling, predictive loops, and their dopaminergic innervation as an error distribution system.

The effects of pallidotomy on Parkinson's disease: study design and assessment techniques

Lesions of the internal segment of the globus pallidus are increasingly being utilized in the surgical treatment of advanced Parkinson's disease, yet studies to demonstrate the safety and efficacy of these procedures are only now being completed. The importance of procedural variations between centres in the outcome of pallidotomy is not yet known. In order to compare accurately results between centres, carefully designed, prospective studies are needed. The authors utilized blinded, randomly evaluated videotaped examinations of pre- and post-operative patients undergoing microelectrode-guided GPi pallidotomy. Their results demonstrate significant effects on contralateral akinesia and tremor in the "off" state, and striking attenuation of levodopa-induced dyskinesias in the "on" state. More modest effects on postural stability and gait disturbance were seen only in non-blinded evaluations. This type of study design should enable many of the outstanding issues related to pallidotomy indications, procedures and outcomes to be addressed.

Surgery for Parkinson's disease

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Controversies in pallidal surgery

Posteroventral pallidotomy (PVP) has gained a worldwide acceptance after its reintroduction by Laitinen et al. in 1992 (56) and many studies have since been published. A review of the recent literature reveals that there is variation in the clinical indications for this procedure, the surgical technique used and the assessment of results. There is no uniform practice in the choice of the anatomical target point within the globus pallidus, the imaging of the target structure, the intraoperative assessment of the physiological target and the mode of evaluation of the surgical results. Although some neurosurgeons advocate that the lesion should be in the lateral pallidum, the majority insist it should be in the medial pallidum. It is shown here that, as long as the lesion is made at the posterior and ventral parts of the globus pallidus, it will necessarily include aspects of both medial and lateral posteroventral pallidum. There is a common agreement on the effectiveness of pallidal surgery on the L-dopa induced dyskinesias, but, its long-term effects on tremor, akinesia, freezing of the gait and other genuine parkinsonian symptoms need more extensive evaluation. The assessment of the outcome of pallidal surgery in terms of the patient's disability, quality of life and coping abilities following surgery seems to have been neglected.

Chronic electrostimulation of ventroposterolateral pallidum: follow-up

Introduced in 1992, and first published with report of 3 cases in 1994, the ventroposterolateral electrostimulation of the pallidum raised exciting prospects. The follow-up of this new approach will be presented in 19 cases with at least 6 months control, and up to 42 months. The very favorable effects observed in the first series could be confirmed and extended to a larger group of patients during a longer period.

Posteroventral pallidotomy in movement disorders

Since 1992 there has been renewed interest in pallidotomy now that the limitations and adverse effects of long-term dopaminergic therapy have become more apparent and more difficult to control in patients with advanced Parkinson's disease. The authors describe the effect of pallidotomy in 19 patients, sixteen of whom had advanced Parkinson's disease with painful dystonia and/or response fluctuations with severe akinesia while in "off" and dyskinesias while in "on". One patient had cortico-basal degeneration with rigidity, one patient had secondary dystonia and one had dystonic posturing due to Wilson's disease. Fifteen patients underwent unilateral pallidotomy, four patients had a staged bilateral procedure. Follow-up ranged from 3 to 42 months (mean 18 months). All patients with peak-dose dyskinesias and/or dystonia had marked reduction of symptoms, including the cases of Wilson's disease and secondary dystonia. The akinesia and rigidity scores of Parkinson-patients in "off" were greatly reduced, mainly but not only on the contralateral side. Evaluation by the patients showed remarkable improvement of symptoms in 79%, leading to substantially improved functional abilities in 68%. In this series the decrease in dopamine-response fluctuations, dystonia, hypokinesia and rigidity with functional improvement as judged by examiners and patients reflect a significant regain of independence.

The side-effects and complications of posteroventral pallidotomy

The side-effects and complications of posteroventral pallidotomy are analysed in 138 consecutive patients who underwent 152 pallidotomies. Transient side-effects, lasting less than three months, appeared in 18% of the patients, that is, 16.5% of the surgical procedures. Long term complications, lasting more than 6 months, were noted in 10% of the patients, that is, 9.2% of the surgical procedures. Sixteen complications occurred alone or in various combinations in 14 patients and included fatigue and sleepiness (2), worsening of memory (4), depression (1), aphonia (1), dysarthria (3), scotoma (1), slight facial and leg paresis (2) and delayed stroke (2). Complications such as dysarthria and paresis could be attributed to MR- or CT-verified pallidal lesions lying too medially and encroaching on the internal capsule. Two of the patients with deterioration in memory had some memory impairment before surgery, and the aphonic patient had dysphonia preoperatively. The study suggests that stereotactic MRI and careful impedance monitoring and macro-stimulation of the posteroventral pallidum area should be sufficient for minimizing the risk of complications; the stereotactic lesion should be centered within the posterior ventral pallidum without involvement of internal capsule. It is concluded that pallidotomy is a safe procedure if performed on cognitively alert patients, and it seems that both the incidence and especially the severity of complications are lower for posteroventral pallidotomy than for thalamotomy.

Gamma knife pallidotomy: case report

We report a case of gamma knife pallidotomy resulting in a permanent contralateral homonymous hemianopsia and transient contralateral hemiparesis with some improvement in contralateral parkinsonian symptoms. This case illustrates the risk of gamma knife pallidotomy which precludes physiologic target localization and can subject structures surrounding the target to a significant radiosurgical dose. Until noninvasive physiologic target localization is available gamma knife pallidotomy and thalamotomy should be limited to patients with an unacceptably high risk for stereotactic percutaneous thermocoagulation.

Selection criteria for unilateral posteroventral pallidotomy

In an attempt to refine the indications for posteroventral pallidotomy (PVP) the authors instituted strict selection criteria which are based on the experience gained from the first 60 pallidotomy patients treated at their institution. In addition to clinical evaluation, all pallidotomy candidates undergo neuropsychological testing and 18F-fluoro-deoxyglucose utilization positron emission tomography (FDG/PET). The data from which these criteria were developed are presented as are early clinical results. The authors demonstrate that these criteria enhance the efficacy of the procedure by assuring therapeutic response and reducing the incidence of post-operative dementia. Their indications and contraindications for pallidotomy are discussed.

Unilateral pallidotomy for Parkinson's disease promptly improves a wide range of voluntary activities--especially gait and trunk movements

26 patients with Parkinson's disease were assessed in the OFF state 2-3 days before and one week after pallidotomy for the time to complete each of 25 standardized motor tasks testing a wide range of voluntary activities important for daily living. After pallidotomy there were substantial improvements across this wide range of activities. Patients completed tasks that they could not perform preoperatively. In general for individual tasks (a) preoperative and postoperative scores were directly related, and (b) the absolute improvement (preop time-postop time) was directly related to preoperative performance: numerical improvements were greater in patients who were worse preoperatively. When the 25 tasks were ranked according to improvement relative to preoperative performance postoperative improvements were successively greater for (a) limbs ipsilateral to pallidotomy, (b) contralateral limbs, and (c) standing and walking. The best results were for activities in which the trunk plays a large part.

Electrophysiologic target localization in posteroventral pallidotomy

The current interest in stereotactic posteroventral pallidotomy (PVP) for treating Parkinson's disease and the variability of published results have raised questions regarding techniques for target localization. In our technique the probe is guided to the optimum target at the most ventral pallidum and ansa lenticularis by macroelectrode stimulation of the internal capsule and optic tract from within the globus pallidus, with the thresholds providing a relative measure of the electrode proximity to these structures. We have characterized these localizing macroelectrode stimulation parameters in 57 posteroventral pallidotomies with consistent anatomic lesion placement, excellent outcome, and no complications. Using a 1.8 x 2.0 mm radiofrequency electrode for macroelectrode stimulation (RFG-3C, Radionics Inc.), minimum voltages (thresholds) to activate motor (at a frequency of 2 Hz) or visual (at a frequency of 100 Hz) responses as well as impedance measurements were obtained at the final target (Tf) and at distances proximal to Tf along the electrode trajectory. The visual and motor threshold voltages at Tf via our standard approach angles (50 degrees above base plane, 20 degrees from the sagittal plane), had a range of 1.0 to 1.5 V, and 2.0 to 3.5 V respectively. We also found that as the probe approaches Tf there is a significant decrease in voltage thresholds for motor (P < .0001) and visual (P < .0001) responses in an individual patient indicating that the probe is converging on these structures. Increases in impedance between Tf, 2-3 mm, and 4-5 mm proximal to Tf were also statistically significant (P < .0001). Microelectrode recording to electrophysiological neuronal activity at various points along the trajectory towards the target showed distinct firing patterns providing identification of the globus pallidus externus and internus, ansa lenticularis, and optic tract. Macroelectrode electrophysiological stimulation within the target volume, inducing threshold responses in the internal capsule and optic tract, provides for accurate localization of the most effective PVP target in the ansa lenticularis. In unresponsive patients, the utilization of microelectrode recording for the identification of the pallidal borders and the optic tract improves safety.

Characteristics and somatotopic organization of kinesthetic cells in the globus pallidus of patients with Parkinson's disease

Information is limited on the characteristics and topographic localization of pallidal kinesthetic cells in patients with Parkinson's disease. The authors analyzed the data from 298 neurons recorded in 38 patients with Parkinson's disease who underwent pallidotomy via microrecording techniques. Sixty-five neurons (22%) responded to passive movement of contralateral limbs. Of 17 kinesthetic cells that were tested in six patients, seven (41%) responded to ipsilateral limb movement as well. Nineteen cells (6%) fired synchronously with tremor. More kinesthetic cells were activated (63%) than inhibited (28%) by movement of single (68%) rather than multiple (32%) joints, and proximal (75%) rather than distal (25%) joints. The lateral globus pallidus externus (GPe) and medial globus pallidus internus (GPi) pallidal segments contained similar proportions of kinesthetic cells, activated or inhibited cells, arm- or leg-activated cells, and cells responding to single or multiple joints. Significantly more kinesthetic cells that responded to distal joints were recorded in GPi compared to GPe segments (p = 0.01). Arm and leg cells had similar characteristics pertaining to activation versus inhibition and responses to single, multiple, proximal, or distal joint movements. Arm and leg cells were somatotopically organized in GPi. Arm cells were clustered at the rostral and caudal segments of GPi and leg cells were clustered centrally. In GPe, leg cells were clustered at the caudal border. No somatotopic organization was identified for activated or inhibited cells; cells that responded to single, multiple, proximal, or distal joints; tremor-synchronous cells; or cells responding to specific joints within somatotopic arm or leg cells. It is concluded that kinesthetic cells provide a roadmap that localizes limb cells during pallidotomy. More studies are needed to identify the clinical significance of the different characteristics of kinesthetic cells.

Glutamate decarboxylase-67 messenger RNA expression in normal human basal ganglia and in Parkinson's disease

Expression of glutamate decarboxylase-67 messenger RNA was examined in the basal ganglia of normal controls and of cases of Parkinson's disease using in situ hybridization histochemistry in human post mortem material. In controls glutamate decarboxylase-67 messenger RNA expression was detected in all large neurons in both segments of the globus pallidus and in three neuronal subpopulations in the striatum as well as in substantia nigra reticulata neurons and in a small sub-population of subthalamic neurons. In Parkinson's disease, there was a statistically significant decrease of 50.7% in glutamate decarboxylase-67 messenger RNA expression per neuron in the lateral segment of the globus pallidus (controls: mean 72.8 microns2 +/- S.E.M. 8.7 of silver grain/neuron, n = 12; Parkinson's disease: mean 35.9 microns2 +/- S.E.M. 9.7 of silver grain/neuron, n = 9, P = 0.01, Student's t-test). In the medial segment of the globus pallidus, there was a small, but non-significant decrease of glutamate decarboxylase-67 messenger RNA expression in Parkinson's disease (controls: mean 100.6 microns2 +/- S.E.M. 7.2 of silver grain/neuron, n = 11; Parkinson's disease: mean 84.8 microns2 +/- S.E.M. 13.0 of silver grain/neuron, n = 7, P = 0.1, Student's t-test). No significant differences in glutamate decarboxylase-67 messenger RNA were detected in striatal neuronal sub-populations between Parkinson's disease cases and controls. These results are the first direct evidence in humans that there is increased inhibitory drive to the lateral segment of the globus pallidus in Parkinson's disease, as suggested by data from animal models. We therefore provide theoretical support for current experimental neurosurgical approaches to Parkinson's disease.

Role of stereotaxis in the treatment of cerebral palsy

There is a renewed interest in basal ganglia surgery for improvement of motor symptoms in cerebral palsy. Rigidity, choreoathetosis, and tremor can be improved or abolished by a well-placed radiofrequency lesion, either in the ventrolateral nucleus of the thalamus or ventroposterior pallidum. The target is chosen based on the predominance of the symptoms in a given patient. A review of the main reports on surgery of the basal ganglia for cerebral palsy, as well as the author's data, shows that the surgery can have a remarkable impact on patients' quality of life when motor dysfunction is improved. An update of the physiopathology of cerebral palsy motor symptoms related to anatomic findings on experimental work, magnetic resonance imaging, and autopsy is used to rationalize surgery of the basal ganglia. Modern stereotactic technique based on exquisite demonstration of the basal ganglia anatomy by magnetic resonance imaging is described and supported by intraoperative electricophysiologic studies. The author stresses the importance of a multidisciplinary approach to provide the cerebral palsy patient with a comprehensive treatment plan before stereotactic surgery.

The basal ganglia: focused selection and inhibition of competing motor programs

The basal ganglia comprise several nuclei in the forebrain, diencephalon, and midbrain thought to play a significant role in the control of posture and movement. It is well recognized that people with degenerative diseases of the basal ganglia suffer from rigidly held abnormal body postures, slowing of movement, involuntary movements, or a combination of these a abnormalities. However, it has not been agreed just what the basal ganglia contribute to normal movement. Recent advances in knowledge of the basal ganglia circuitry, activity of basal ganglia neurons during movement, and the effect of basal ganglia lesions have led to a new hypothesis of basal ganglia function. The hypothesis states that the basal ganglia do not generate movements. Instead, when voluntary movement is generated by cerebral cortical and cerebellar mechanisms, the basal ganglia act broadly to inhibit competing motor mechanisms that would otherwise interfere with the desired movement. Simultaneously, inhibition is removed focally from the desired motor mechanisms to allow that movement to proceed. Inability to inhibit competing motor programs results in slow movements, abnormal postures and involuntary muscle activity.

Effects of L-DOPA-therapy on dopamine D2 receptor mRNA expression in the striatum of MPTP-intoxicated parkinsonian monkeys

The cellular expression of dopamine D2 receptor mRNA was examined in striatal (caudate nucleus and putamen) neurones of 9 Macaca fascicularis monkeys rendered parkinsonian by systemic injection of MPTP. Messenger RNA abundance was determined by quantitative in situ hybridization using human-specific 35S-labelled oligonucleotides. Control monkeys were untreated and received neither MPTP nor L-DOPA while the rest were rendered parkinsonian and received chronic levodopa therapy to induce dyskinesia. In the control brains a strong dopamine D2 receptor hybridization signal was detected overlying medium-sized and some large neurons in both the caudate nucleus and putamen. Neurons from the lateral and medial regions of the caudate nucleus, and from the dorsal and ventral regions of the putamen were analysed separately. A significant increase in the cellular abundance of dopamine D2 receptor mRNA was seen in the striatum of MPTP-treated monkeys; this increase being restricted to the population of medium-sized striatal cells. No such increase in dopamine D2 receptor mRNA was observed in (dyskinetic) L-DOPA-treated monkeys suggesting that levodopa-therapy normalises D2 receptor expression in post-synaptic striatal cells. The cellular abundance of dopamine D2 receptor mRNA expressed by large striatal neurons (putative cholinergic cells) was unaffected by either MPTP treatment or levodopa therapy. The implications of these findings for the development of levodopa-induced dyskinesias is discussed.

Pallidotomy: a survey of current practice in North America

Twenty-eight centers completed a survey about their current practice of pallidotomy. This sample represents a non-exhaustive survey of the current practice of pallidotomy in North America and is not a study of outcomes. 1015 patients underwent 1219 pallidotomies: 811 (80%) unilateral, 72 (7%) staged bilateral, and 132 (13%) simultaneous bilateral. Pallidotomy has long been an accepted procedure and the indications for this surgery, in the opinion of the responding centers, were rated on a scale of 1 (poor) to 4 (excellent) and demonstrated dyskinesia as the best indication (median = 4); on-off fluctuations, dystonia, rigidity, and bradykinesia as good indications (median = 3); and freezing, tremor and gait disturbance as fair indications (median = 2). Most centers used MRI alone (50%) or in combination with CT scan (n = 6) or ventriculopathy (n = 5) to localize the target. The median values of pallidal coordinates were: 2 mm anterior to the midcommissural point 21 mm lateral to the midsagittal plane and 5 mm below the intercommissural line. Microrecording was performed by half of the centers (n = 14) and half of the remaining centers were considering starting it (n = 7). Main criteria used to define the target included the firing pattern of spontaneous neuronal discharges (n = 13) and the response to joint movement (n = 10). Most centers performed motor (n = 26) and visual (n = 23) macrostimulation. Twenty four centers performed test lesions using median values of 55 degrees C temperatures for 30 s. Final lesions consisted of 3 permanent lesions placed 2 mm apart, each lesion created with median values of 75 degrees C temperatures for 1 minute. Median hospital stay was 2 days.

Treatment of advanced Parkinson's disease by posterior GPi pallidotomy: 1-year results of a pilot study

The effects of posterior internal pallidal ablation (GPi pallidotomy) on parkinsonian signs and symptoms were studied in 15 patients with medically intractable Parkinson's disease (PD). The sensorimotor territory of the internal portion of the globus pallidus and the adjacent optic tract and internal capsule were identified with microelectrode recording and stimulation. Radiofrequency lesions were then created in the identified sensorimotor territory. Pallidotomy significantly improved all cardinal parkinsonian motor signs (tremor, rigidity, akinesia/bradykinesia, and gait dysfunction) and reduced drug-induced motor fluctuations and dyskinesias. The improvements occurred predominately contralateral to the lesion, but were also present ipsilaterally. Early postoperative (3-month), mean total United Parkinson's Disease Rating Scale scores improved by 30.1% from preoperative values. Mean combined "on/off" Schwab and England Scale scores, a measure of functional independence, increased from 48.8% to 73.0% postoperatively. The mean total United Parkinson's Disease Rating Scale and Schwab and England scores did not show a statistically significant decline over the 1-year postoperative period. Surgery resulted in little morbidity, including a lack of significant deficits on neuropsychological and psychiatric testing. Physical and social functioning and vitality measures on the Medical Outcome Scale also showed significant improvement over the postoperative period. The findings of this pilot study demonstrate that ablation of the sensorimotor portion of the internal pallidum is a highly effective treatment for advanced PD, with benefits sustained at 1 year.

High frequency stimulation of the internal Globus Pallidus (GPi) simultaneously improves parkinsonian symptoms and reduces the firing frequency of GPi neurons in the MPTP-treated monkey

The firing pattern of the neurons of the internal Globus Pallidus (GPi) is greatly disturbed in Parkinson's disease. Surgical lesion or high frequency stimulation (HFS) of the GPi reduces parkinsonian rigidity and akinesia. We evaluated in this study the effects of HFS of the GPi on the firing pattern of its neurons. Extracellular recordings were carried out under three types of experimental conditions in rhesus monkeys, normal state, after MPTP treatment and during HFS of the GPi. After intracarotidian MPTP injection, the firing rate of GPi cells increased significantly. During HFS, MPTP-induced parkinsonian motor symptoms clearly improved correlatively with a significant decrease in the firing rate of GPi cells in the stimulated area. HFS restored a firing frequency similar to that in normal animals and, unexpectedly, did not completely block neuronal activity.

CT-target determination in postero-ventral pallidotomy: a universal method. Technical note

Stereotactic targeting of the postero-ventral pallidum (PVP) presents special challenges to the surgeon 1) The target is in intimate relation to the optic tract and the internal capsule. 2) Proper angulation of the trajectory is crucial to achieve optimal effects given the long craniocaudal extension of the PVP. 3) The PVP is difficult to identify on computerized tomography (CT): the border between the internal capsule and the pallidum is usually not apparent. Potential sources of error in target determination include: - angulation of the scanning plane in relation to the intercommissural plane; - projection of the reference points (anterior commissure/posterior commissure [AC/PC]) results in the foreshortened intercommissural line, affecting the Y co-ordinate; - small tilts between the CT gantry and the stereotactic frame affect determination of the X and Z co-ordinates. Correction of these sources of error is done with basic trigonometric algorithms. The authors have developed a rapid method of stereotactic co-ordinate calculation which avoids the need to perform error-prone calculations under the pressure of operating room conditions. 1) The frame is applied with its basal plane corresponding roughly to the orbito-meatal line. 2) Thin CT slices (2 mm increments) are obtained through the area of interest and the slices are printed. 3) The major reference points (Foramen of Monro, AC, PC) are identified and marked. The PC point is projected onto the film containing AC (or viceversa if the PC slice is caudal to AC). 4) The intercommissural distance is measured, and the true length is obtained from a correction graph. The Y co-ordinate is then calculated as 1/2 ICL + 2 mm [towards AC]. 5) The slice corresponding to the target [Z co-ordinate] is obtained from a correction graph that takes into consideration the gap [number of slices] between AC and PC. 6) The X co-ordinate is placed 20 to 22 mm from midline. A graph that takes into consideration the coronal tilt of the stereotactic frame in relation to the CT gantry allows for final corrections of the X and Z co-ordinates. This step-by-step simple method of co-ordinate calculation can be used with any CT-compatible stereotactic frame.

Regional metabolic correlates of surgical outcome following unilateral pallidotomy for Parkinson's disease

Stereotaxic ventral pallidotomy has been employed in the symptomatic treatment of patients with advanced Parkinson's disease (PD). To understand the pathophysiology of clinical outcome following this procedure, we studied 10 PD patients (5 men and 5 women; mean age 60.0 +/- 6.1 years; mean Hoehn and Yahr stage 3.8 +/- 1.0) with quantitative 18F-fluorodeoxyglucose (FDG) and positron emission tomography (PET). All patients were scanned preoperatively; 8 of 10 patients were rescanned 6 to 8 months following surgery. Clinical performance was assessed off medications before and after surgery using standardized timed motor tasks. We found that preoperative lentiform metabolism correlated significantly with improvement in contralateral motor tasks at 1 week, 3 months, and 6 months following unilateral pallidotomy (p<0.03). Postoperatively, significant metabolic increases were noted in the primary motor cortex, lateral premotor cortex, and dorsolateral prefrontal cortex (p<0.01) of the hemisphere that underwent surgery. Improvement in contralateral limb motor performance correlated significantly with surgical declines in thalamic metabolism (p<0.01) and increases in lateral frontal metabolism (p<0.05). Principal components analysis disclosed a significant covariance pattern characterized by postoperative declines in ipsilateral lentiform and thalamic metabolism associated with bilateral increase in supplementary motor control metabolism. Subject scores for this pattern correlated significantly with improvements in both contralateral and ipsilateral limb performance (p<0.005). These results suggest that pallidotomy reduced the preoperative overaction of the inhibitory pallidothalamic projection. Clinical improvement may be associated with modulations in regional brain metabolism occurring remote from the lesion site.

Gamma knife pallidotomy in advanced Parkinson's disease

Posteroventral pallidotomy as a treatment for Parkinson's disease (PD) has been the subject of increasing interest. We treated 4 nondemented patients with advanced PD, 2 with severe bradykinesia and a declining response to medication, and 2 with marked clinical fluctuations. All patients received 180 Gy delivered in one sitting to the right posteroventral pallidum site, used by Laitinen and colleagues, adjusted as needed, to avoid the optic tract. Only 1 patient changed significantly. Dyskinesia completely resolved on the side contralateral to the lesion in this patient. This same patient also became transiently demented and psychotic. The other 3 patients suffered no clearly identifiable beneficial or harmful effects. Follow-up magnetic resonance imaging scans of the brain at 1 year revealed lesions exactly where targeted although of unequal sizes. Our negative experience forces us to conclude that either larger volumes of tissue must be ablated, that physiologic monitoring is required for placing a lesion, that our subjects were poor candidates for the procedure, or that surgical ablation and radiation cause tissue damage of different types with different results.

Central mechanisms of tremor

Physiologic and pathologic tremors are mechanistically classified into two broad groups: (1) those produced by oscillation in sensorimotor loops, so-called mechanical-reflex tremors, and (2) those produced by the oscillatory properties of central neuronal networks. This review provides a contemporary perspective of tremor pathophysiology while acknowledging that no form of tremor is understood completely. Indeed, the origin of oscillation in most forms of tremor is undefined, and in many instances the underlying pathology is unknown.

Methods for microelectrode-guided posteroventral pallidotomy

Methods for localizing the posteroventral globus pallidus intermus are described. The authors' techniques include the use of microelectrodes to record single-unit activity and to microstimulate in human pallidum and its surrounding structures. This technique allows a precise determination of the locations of characteristic cell types in sequential trajectories through the external and internal segments of the pallidum. The location of the optic tract can be determined from microstimulation-evoked visual sensations and recordings of flash-evoked potentials. In addition, microstimulation-evoked motor and sensory responses allow the internal capsule to be identified. The data collected using this technique are an important adjunct to selecting optimum sites to place electrocoagulation lesions for stereotactic posteroventral pallidotomy for refractory Parkinson's disease.

Simultaneous bilateral pallidoansotomy for idiopathic dystonia musculorum deformans

A 17-year-old Russian male with a 9-year diagnosed history of dystonia musculorum deformans manifested as severe tortipelvis, lordosis, and axial and appendicular spastic dystonia, refractory to medical therapy, is reported. This patient underwent a simultaneous bilateral pallidoansotomy with dramatic results. Postoperative evaluation revealed sustained alleviation of all dystonic symptoms and abnormal movements. Rapid recovery of useful strength in all limbs as well as dramatic improvement in coordination occurred. Bilateral posteroventral pallidotomy and pallidoansotomy in the past have proven effective in alleviation of all parkinsonian symptoms, including dyskinesia and dystonia, without the concurrent risk of intransigent side effects associated with bilateral thalamotomy or other stereotactic surgical procedures. Pallidoansotomy may prove to be the treatment of choice for idiopathic torsion dystonia and merits further investigation.

Effect of GPi pallidotomy on motor function in Parkinson's disease

The major motor disturbances in Parkinson's disease are thought to be caused by overactivity of the internal segment of the globus pallidus (GPi), in large part due to excessive drive from the subthalamic nucleus. The excessive inhibitory activity of GPi is thought to "brake' the motor thalamus and the cortical motor system to produce the slowness, rigidity, and poverty of movement characteristic of parkinsonian states. To test the hypothesis that direct reduction of Gpi activity can improve motor function, we studied the effect of GPi pallidotomy in 14 patients. The location of the GPi nucleus was confirmed by microelectrode recording before lesion creation. Standardised videotape recordings before and after operation were randomised and scored by a "blinded' evaluator. 6 months after surgery, total motor score in the "off" state had improved by 30% and the total akinesia score by 33%. The gait score in the "off" state improved by 15% and a composite postural instability and gait score by 23%. After surgery there was almost total elimination of drug-induced involuntary movements (dyskinesias), with a 92% reduction on the side contralateral to the pallidotomy. No patient had visual or corticospinal complications. In these patients GPi pallidotomy enhanced motor performance, reduced akinesia, improved gait, and eliminated the neural elements responsible for levodopa-induced dyskinesias.

Apoptosis of neurons in the vestibular nuclei of adult mice results from prolonged change in the external environment

Pharmacological manipulations which result in abnormal levels of excitatory amino acid (EAA) mediated neurotransmission can result in neuronal apoptosis. We accordingly hypothesised that manipulations of the external environment which induce prolonged EAA-mediated transmission in sensory neurons may also induce apoptosis. This hypothesis was tested by placing groups of adult mice, housed in their home cage, on a turntable which slowly rotated (0.8 rev./min). This non-invasive manipulation will have resulted in abnormal discharge patterns in the vestibular nuclei. Significantly greater levels of neuronal apoptosis were seen in the vestibular complex after rotation for 48 h compared with non-rotated controls. This finding was also predicted independently from a computational approach.

Effects of L-DOPA on preproenkephalin and preprotachykinin gene expression in the MPTP-treated monkey striatum

The cellular expression of the genes encoding the neuropeptides enkephalin and substance P were examined in the caudate nucleus and putamen of parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgus monkeys by in situ hybridization using radioactive antisense oligonucleotides coupled with computer-assisted image analysis. Behavioural evaluation of the animals revealed two levels of motor impairment; one group moderately impaired and the other severely disabled. A marked increase in the cellular content of preproenkephalin A messenger RNA was observed in medium-sized (106 +/- 9 microns2) cells in the caudate-putamen of all MPTP animals when compared with controls, the increase being greatest in the most severely impaired animals. By contrast, a marked reduction in the cellular abundance of preprotachykinin gene expression was detected in striatal cells (101 +/- 16 microns2) of these same MPTP animals. These changes in neuropeptide gene expression were not associated with a change in the density (approximately 10 cells per mm2) of messenger RNA-expressing cells. L-DOPA treatment of two of the severely-impaired MPTP monkeys resulted in a dissociation of expression of these two genes: the cellular abundance of preproenkephalin A remained elevated whilst preprotachykinin levels were normalized and comparable with controls. No change in the cellular abundance of preprotachykinin messenger RNA was observed in cells of the insular cortex or a small discrete population of large cells (208 +/- 27 microns2) in the ventral putamen. These results demonstrate that MPTP treatment of primates results in a marked potentiation in preproenkephalin messenger RNA coupled with a attenuation in preprotachykinin messenger RNA in the dopamine-denervated caudate-putamen. L-DOPA therapy given on an intermittent schedule reverses the decrease in preprotachykinin messenger RNA, but fails to reverse the increase in preproenkephalin messenger RNA in the same animal. These observations suggest that a dissociation of the activity of these two neuropeptide systems may underlie the improvement in motor skill that accompanies dopamine replacement therapy and that this dissociation may be instrumental in the long-term complications associated with L-DOPA therapy.

A neural model of basal ganglia-thalamocortical relations in normal and parkinsonian movement

Anatomical, neurophysiological, and neurochemical evidence supports the notion of parallel basal ganglia-thalamocortical motor systems. We developed a neural network model for the functioning of these systems during normal and parkinsonian movement. Parkinson's disease (PD), which results predominantly from nigrostriatal pathway damage, is used as a window to examine basal ganglia function. Simulations of dopamine depletion produce motor impairments consistent with motor deficits observed in PD that suggest the basal ganglia play a role in motor initiation and execution, and sequencing of motor programs. Stereotaxic lesions in the model's globus pallidus and subthalamic nucleus suggest that these lesions, although reducing some PD symptoms, may constrain the repertoire of available movements. It is proposed that paradoxical observations of basal ganglia responses reported in the literature may result from regional functional neuronal specialization, and the non-uniform distributions of neurochemicals in the basal ganglia. It is hypothesized that dopamine depletion produces smaller-than-normal pallidothalamic gating signals that prevent rescalability of these signals to control variable movement speed, and that in PD can produce smaller-than-normal movement amplitudes.

Outcome after stereotactic thalamotomy for parkinsonian, essential, and other types of tremor

A better understanding of the mechanisms underlying movement disorders, coupled with refinements in surgical technique, has led to a resurgence of interest in the surgical treatment of patients with tremor. We retrospectively analyzed the outcomes of 60 patients (62 patient sides) with medically intractable tremor who underwent stereotactic thalamotomy. Of these 60 patients, 42 had Parkinson's disease (of whom 2 patients underwent bilateral surgery for a total of 44 patient sides), 6 had essential tremor, 6 had cerebellar tremor, and 6 had post-traumatic tremor. The patients received follow-up for as long as 13 years (mean, 53.4 mo) after their operations. At the most recent follow-up visit, 86% of the patients with Parkinson's disease, 83% of the patients with essential tremor, 67% of the patients with cerebellar tremor, and 50% of the patients with post-traumatic tremor had cessation of or moderate-to-marked improvement in their contralateral tremor, with a concomitant improvement in function. The mean daily dose of levodopa for those patients preoperatively taking levodopa (n = 35) was reduced by approximately 156 mg at a mean of 53.4 months after thalamotomy. Immediate postoperative complications were common, occurring in 58% of patients. The most common complications were contralateral weakness (34%), dysarthria (29%), and confusion (23%). These complications generally resolved rapidly during the postoperative period.

Bilateral subthalamic nucleus stimulation for severe Parkinson's disease

Subthalamic nucleus (STN) lesions or high-frequency stimulations could improve parkinsonian symptoms in monkeys treated by MPTP. We have applied the procedure of chronic stimulation to the STN in severely disabled parkinsonian patients. This article presents the case of the first patient operated on bilaterally. Bilateral STN stimulation has greatly improved akinesia and rigidity. The benefit was maintained < or = 15 months after surgery. Unilateral stimulation induced motor effects mainly in contralateral limbs. Further studies are needed to evaluate the value of this procedure in the treatment of Parkinson's disease.