Chronic anterior pallidal stimulation for Parkinson's disease

Neuropsychological performance changes following subthalamic versus pallidal deep brain stimulation in Parkinson's disease: a systematic review and metaanalysis

BACKGROUND

Studies comparing subthalamus (STN) and globus pallidus internus (GPi) deep brain stimulation (DBS) for the management of Parkinson's disease in terms of neuropsychological performance are scarce and heterogeneous. Therefore, we performed a systematic review and metaanalysis to compare neuropsychological outcomes following STN DBS versus GPi DBS.

METHODS

A computer literature search of PubMed, the Web of Science, and Cochrane Central was conducted. Records were screened for eligible studies, and data were extracted and synthesized using Review Manager (v. 5.3 for Windows).

RESULTS

Seven studies were included in the qualitative synthesis. Of them, four randomized controlled trials (n=345 patients) were pooled in the metaanalysis models. The standardized mean difference (SMD) of change in the Stroop color-naming test favored the GPi DBS group (SMD=-0.31, p=0.009). However, other neuropsychological outcomes did not favor either of the two groups (Stroop word-reading: SMD=-0.21, p=0.08; the Wechsler Adult Intelligence Scale (WAIS) digits forward: SMD=0.08, p=0.47; Trail Making Test Part A: SMD=-0.05, p=0.65; WAIS-R digit symbol: SMD=-0.16, p=0.29; Trail Making Test Part B: SMD=-0.14, p=0.23; Stroop color-word interference: SMD=-0.16, p=0.18; phonemic verbal fluency: bilateral DBS SMD=-0.04, p=0.73, and unilateral DBS SMD=-0.05, p=0.83; semantic verbal fluency: bilateral DBS SMD=-0.09, p=0.37, and unilateral DBS SMD=-0.29, p=0.22; Boston Naming Test: SMD=-0.11, p=0.33; Beck Depression Inventory: bilateral DBS SMD=0.15, p=0.31, and unilateral DBS SMD=0.36, p=0.11).

CONCLUSIONS

There was no statistically significant difference in most of the neuropsychological outcomes. The present evidence does not favor any of the targets in terms of neuropsychological performance.

Combined Vision and Wearable Sensors-based System for Movement Analysis in Rehabilitation

Background: Traditional rehabilitation sessions are often a slow, tedious, disempowering and non-motivational process, supported by clinical assessment tools, i.e. evaluation scales that are prone to subjective rating and imprecise interpretation of patient’s performance. Poor patient motivation and insufficient accuracy are thus critical factors that can be improved by new sensing/processing technologies.

Objectives: We aim to develop a portable and affordable system, suitable for home rehabilitation, which combines vision-based and wearable sensors. We introduce a novel approach for examining and characterizing the rehabilitation movements, using quantitative descriptors. We propose new Movement Performance Indicators (MPIs) that are extracted directly from sensor data and quantify the symmetry, velocity, and acceleration of the movement of different body/hand parts, and that can potentially be used by therapists for diagnosis and progress assessment.

Methods: First, a set of rehabilitation exercises is defined, with the supervision of neurologists and therapists for the specific case of Parkinson’s disease. It comprises full-body movements measured with a Kinect device and fine hand movements, acquired with a data glove. Then, the sensor data is used to compute 25 Movement Performance Indicators, to assist the diagnosis and progress monitoring (assessing the disease stage) in Parkinson’s disease. A kinematic hand model is developed for data verification and as an additional resource for extracting supplementary movement information.

Results: Our results show that the proposed Movement Performance Indicators are relevant for the Parkinson’s disease assessment. This is further confirmed by correlation of the proposed indicators with clinical tapping test and UPDRS clinical scale. Classification results showed the potential of these indicators to discriminate between the patients and controls, as well as between the stages that characterize the evolution of the disease.

Conclusions: The proposed sensor system, along with the developed approach for rehabilitation movement analysis have a significant potential to support and advance traditional rehabilitation therapy. The main impact of our work is two-fold: (i) the proposition of an approach for supporting the therapists during the diagnosis and monitoring evaluations by reducing subjectivity and imprecision, and (ii) offering the possibility of the system to be used at home for rehabilitation exercises in between sessions with doctors and therapists.

Applications of Electrical Pacing in the Body

Gastric electrostimulation by a pulse generator is an area of intense interest for the treatment of obesity. The concept of a rhythmic electrical current applied to neural or myal tissues has been established for the treatment of major problems in many areas of the body or is being investigated.

Deep brain stimulation in the treatment of neurological and psychiatric disease

Deep brain stimulation has become a topic of intense interest both from a clinical and basic science perspective. Its indications, currently including Parkinson's disease, tremor and dystonia, may expand in the future to include not only other movement disorders but also epilepsy, obsessive-compulsive disorder and other neuropsychiatric conditions. The mechanism(s) of action of deep brain stimulation have only recently begun to be characterized and have already yielded surprises that may open the door to a greater expansion of the indications for this novel and powerful therapeutic intervention.

Prosthetic systems for therapeutic optical activation and silencing of genetically-targeted neurons

Many neural disorders are associated with aberrant activity in specific cell types or neural projection pathways embedded within the densely-wired, heterogeneous matter of the brain. An ideal therapy would permit correction of activity just in specific target neurons, while leaving other neurons unaltered. Recently our lab revealed that the naturally-occurring light-activated proteins channelrhodopsin-2 (ChR2) and halorhodopsin (Halo/NpHR) can, when genetically expressed in neurons, enable them to be safely, precisely, and reversibly activated and silenced by pulses of blue and yellow light, respectively. We here describe the ability to make specific neurons in the brain light-sensitive, using a viral approach. We also reveal the design and construction of a scalable, fully-implantable optical prosthetic capable of delivering light of appropriate intensity and wavelength to targeted neurons at arbitrary 3-D locations within the brain, enabling activation and silencing of specific neuron types at multiple locations. Finally, we demonstrate control of neural activity in the cortex of the non-human primate, a key step in the translation of such technology for human clinical use. Systems for optical targeting of specific neural circuit elements may enable a new generation of high-precision therapies for brain disorders.

Multiple-color optical activation, silencing, and desynchronization of neural activity, with single-spike temporal resolution

The quest to determine how precise neural activity patterns mediate computation, behavior, and pathology would be greatly aided by a set of tools for reliably activating and inactivating genetically targeted neurons, in a temporally precise and rapidly reversible fashion. Having earlier adapted a light-activated cation channel, channelrhodopsin-2 (ChR2), for allowing neurons to be stimulated by blue light, we searched for a complementary tool that would enable optical neuronal inhibition, driven by light of a second color. Here we report that targeting the codon-optimized form of the light-driven chloride pump halorhodopsin from the archaebacterium Natronomas pharaonis (hereafter abbreviated Halo) to genetically-specified neurons enables them to be silenced reliably, and reversibly, by millisecond-timescale pulses of yellow light. We show that trains of yellow and blue light pulses can drive high-fidelity sequences of hyperpolarizations and depolarizations in neurons simultaneously expressing yellow light-driven Halo and blue light-driven ChR2, allowing for the first time manipulations of neural synchrony without perturbation of other parameters such as spiking rates. The Halo/ChR2 system thus constitutes a powerful toolbox for multichannel photoinhibition and photostimulation of virally or transgenically targeted neural circuits without need for exogenous chemicals, enabling systematic analysis and engineering of the brain, and quantitative bioengineering of excitable cells.

Deep brain stimulation in Parkinson disease: a metaanalysis of patient outcomes

Object. Deep brain stimulation (DBS) to treat advanced Parkinson disease (PD) has been focused on one of two anatomical targets: the subthalamic nucleus (STN) and the globus pallidus internus (GPI). Authors of more than 65 articles have reported on bilateral DBS outcomes. With one exception, these studies involved pre- and postintervention comparisons of a single target. Despite the paucity of data directly comparing STN and GPI DBS, many clinicians already consider the STN to be the preferred target site. In this study the authors conducted a metaanalysis of the existing literature on patient outcomes following DBS of the STN and the GPI.

Methods. This metaanalysis includes 31 STN and 14 GPI studies. Motor function improved significantly following stimulation (54% in patients whose STN was targeted and 40% in those whose GPI was stimulated), with effect sizes (ESs) of 2.59 and 2.04, respectively. After controlling for participant and study characteristics, patients who had undergone either STN or GPI DBS experienced comparable improved motor function following surgery (p = 0.094). The performance of activities of daily living improved significantly in patients with either target (40%). Medication requirements were significantly reduced following stimulation of the STN (ES = 1.51) but did not change when the GPI was stimulated (ES = −0.02).

Conclusions. In this analysis the authors highlight the need for uniform, detailed reporting of comprehensive motor and nonmotor DBS outcomes at multiple time points and for a randomized trial of bilateral STN and GPI DBS.

Kinematic evaluation in Parkinson's disease using a hand-held position transducer and computerized signal analysis

BACKGROUND

The objective of this work was to develop a device for quantification of akinesia in Parkinson's disease, for the use in home monitoring of PD patients, as a part of home telecare programs. For this purpose a simple movement task is to be preferred, and the measurement devices must be small, lightweight, and easy to use, so patients may perform the measurements unattended. Another intended application was optimisation of the electrode position during implantations of neuromodulation systems for treatment of Parkinson.

METHOD

A hand held transducer was used to measure the position of the thumb while the patient repeatedly flexed and extended the thumb. The position data was sampled and stored on a personal computer with a plug in converter card and software. Measurements were performed on 15 PD patients and 6 age-matched controls. Signal analysis procedures were developed in order to automatically derive numerical parameters that quantify the movement performance. In order to select the most relevant parameters, they were correlated to Unified Parkinson Disease Rating Scale (UPDRS) motor scores (Spearman's rank, single sided, p < 0.05).

FINDINGS

In reviews of the raw position signals the amplitude and frequency was found to be lower in patients than in controls. In patients the movement was frequently interrupted by short periods of hesitation. The calculated parameters of covered distance (correlation coefficient r = -0.63), hesitation (r = 0.64) and frequency (r = -0.6) were found to be most relevant, as they correlated best to the UPDRS hand pronation/supination score.

DISCUSSION

The equipment proved to be fast to setup and easy to use. The signal analysis methods provided meaningful numerical parameters for quantification of akinesia, represented in hand pronation/supination. These results suggest that the described methods may be useful for telemedicine and intraoperative use.

Long-term pallidal deep brain stimulation in patients with advanced Parkinson disease: 1-year follow-up study

OBJECT

The goal of this study was to investigate the efficacy of long-term deep brain stimulation (DBS) of the posteroventral lateral globus pallidus internus (GPi) accomplished using a single-contact monopolar electrode in patients with advanced Parkinson disease (PD).

METHODS

Sixteen patients suffering from severe PD and levodopa-induced side effects such as dyskinesias and on-off fluctuations were enrolled in a prospective study protocol. There were six women and 10 men and their mean age at surgery was 65 years. All patients underwent implantation of a monopolar electrode in the posteroventral lateral GPi. Initially, nine patients received unilateral stimulation. Three of these patients underwent contralateral surgery at a later time. Ten patients received bilateral stimulation (contemporaneous bilateral surgery was performed in seven patients and staged bilateral surgery in the three patients who had received unilateral stimulation initially). Formal assessments were performed during both off-medication and on-medication (levodopa) periods preoperatively, and at 3 and 12 months postoperatively. There were no serious complications related to surgery or to DBS. Two transient adverse events occurred: in one patient a small pallidal hematoma developed, resulting in a prolonged micropallidotomy effect, and in another patient a subcutaneous hemorrhage occurred at the site of the pacemaker. In patients who received unilateral DBS, the Unified Parkinson's Disease Rating Scale activities of daily living (ADL) score during the off-levodopa period decreased from 30.8 at baseline to 20.4 at 3 months (34% improvement) and 20.6 at 12 months (33% improvement) postoperatively. The motor score during the off period improved from 57.2 at baseline to 35.2 at 3 months (38% improvement) and 35.3 at 12 months (38% improvement) postoperatively. Bilateral DBS resulted in a reduction in the ADL score during the off period from 34.9 at baseline to 22.3 at 3 months (36% improvement) and 22.9 at 12 months (34% improvement). The motor score for the off period changed from 63.4 at baseline to 40.3 at 3 months (36% improvement) and 37.5 at 12 months (41% improvement). In addition, there were significant improvements in patients' symptoms during the on period and in on-off motor fluctuations.

CONCLUSIONS

Pallidal DBS accomplished using a monopolar electrode is a safe and effective procedure for treatment of advanced PD. Compared with pallidotomy, the advantages of pallidal DBS lie in its reversibility and the option to perform bilateral surgery in one session. Comparative studies in which DBS is applied to other targets are needed.

Deep brain stimulation of the subthalamic nucleus in Parkinson's disease: comparison of pre- and postoperative neuropsychological evaluation

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for the motor symptoms of advanced Parkinson's disease (PD). The aim of this study was to assess the effect of the bilateral surgical procedure and STN DBS on the neuropsychological functions. Twenty Parkinson's disease patients underwent a neuropsychological assessment before and 6 months after surgery in four different conditions: medication on (with levodopa) and medication off (without levodopa) during the preoperative period, medication on/stimulation on (levodopa plus stimulators switched on) and medication off/stimulation on (stimulators switched on without levodopa) during the postoperative period. We did not find any significant difference in the four conditions for all the neuropsychological tests, confirming the lack of an overall cognitive decline after surgery. From a neuropsychological point of view, these results seem to indicate that bilateral STN DBS is a safe treatment for advanced PD.

Deep brain stimulation for the treatment of Parkinson's disease: subthalamic nucleus versus globus pallidus internus

OBJECTIVES

Deep brain stimulation of the basal ganglia has become a promising treatment option for patients with Parkinson's disease who have side effects from drugs. Which is the best target-globus pallidus internus (GPi) or subthalamic nucleus (STN)-is still a matter of discussion. The aim of this prospective study is to compare the long term effects of GPi and STN stimulation in patients with severe Parkinson's disease.

PATIENTS AND METHODS

Bilateral deep brain stimulators were implanted in the GPi in six patients and in the STN in 12 patients with severe Parkinson's disease. Presurgery and 3, 6, and 12 months postsurgery patients were scored according to the CAPIT protocol.

RESULTS

Stimulation of the STN increased best Schwab and England scale score significantly from 62 before surgery to 81 at 12 months after surgery; GPi stimulation did not have an effect on the Schwab and England scale. Stimulation of the GPi reduced dyskinesias directly whereas STN stimulation seemed to reduce dyskinesias by a reduction of medication. Whereas STN stimulation increased the unified Parkinson's disease rating scale (UPDRS) motor score, GPi stimulation did not have a significant effect. Fluctuations were reduced only by STN stimulation and STN stimulation suppressed tremor very effectively.

CONCLUSION

Stimulation of the GPi reduces medication side effects, which leads to a better drug tolerance. There was no direct improvement of bradykinesia or tremor by GPi stimulation. Stimulation of the STN ameliorated all parkinsonian symptoms. Daily drug intake was reduced by STN stimulation. The STN is the target of choice for treating patients with severe Parkinson's disease who have side effects from drugs.

Double blinded evaluation of the effects of pallidal and subthalamic nucleus stimulation on daytime activity in advanced Parkinson's disease

The results of a double blinded evaluation of the effects of globus pallidus (GPi; n=7) and subthalamic nucleus (STN; n=11) stimulation in patients with advanced Parkinson's disease are summarized. The patients were evaluated at 6-8months after surgery. In order to determine the benefits afforded by the stimulation to the actual daily activities, the patients were maintained on-medication with optimal doses and schedules. The stimulation was turned off overnight for at least 12h. It was turned on in the morning (or maintained turned off), and the best and worst scores during daytime activity were recorded, as on-period and off-period scores, respectively. A reduction in total motor score on the Unified Parkinson's Disease Rating Scale was clearly elicited by GPi and STN stimulation at both the off-period (-57 and -29%, respectively) and the on-period (-36 and -25%, respectively). The difference in effects between GPi and STN stimulation appeared to be due largely to an unintended difference in the patients' preoperative symptoms. The benefits provided by stimulation to the actual daily activities appears to be limited in patients who have become unresponsive to a large dose of levodopa. Two advantages of GPi and STN stimulation were identified. Firstly, the stimulation can supplement a reduced action of levodopa during the off-period. It thus improves the patient's daily activities through attenuation of the motor fluctuations. Secondly, the stimulation can replace part of the action of levodopa during the on-period. It thus attenuates dopa-induced dyskinesia through a reduced dose of medication. More importantly, the stimulation improves the daily activities in dopa-intolerant patients who are being administered a small dose of levodopa because of unbearable side effects. In addition, GPi stimulation has its own inhibitory effect on dopa-induced dyskinesia. Clinically important improvement was observed in severe gait freezing in 2 patients following unilateral anterodorsal GPi stimulation on the right side alone.

Acute and chronic effects of anteromedial globus pallidus stimulation in Parkinson's disease

OBJECTIVE

To evaluate the effects of acute and chronic stimulation in the anteromedial part of the globus pallidus internus (GPi) on the symptoms of patients with Parkinson's disease.

METHODS

Six patients with severe Parkinson's disease (Hoehn and Yahr stage 4-5 in "off" drug condition) with motor fluctuations and levodopa induced dyskinesia (LID) were operated on. Chronic electrodes were implanted in the anteromedial GPi bilaterally in five patients and unilaterally in one patient. The effect of stimulation via the four contacts for each electrode (n=11) was assessed postoperatively on the contralateral parkinsonian signs in the off condition and on the contralateral and ipsilateral LID in the "on" condition. The core assessement program for intracerebral transplantation protocol was performed before surgery and then 1, 3, and 6 months after surgery in on and off conditions and in on and off stimulation conditions.

RESULTS

Stimulation performed postoperatively showed a significant improvement (p<0.05) by 47% (contralateral rigidity) and 32% (contralateral bradykinesia) when stimulation was applied through the distal contact. Levodopa induced dyskinesias were improved by 95% (contralateral LID) and by 66% (ipsilateral LID) when stimulation was applied through the distal contact. Six months after the surgery, GPi stimulation in the off condition led to a mean improvement in the motor score of UPDRS by 36%. The mean daily duration in the off state decreased by 52% (p<0.05). The mean duration of LIDs decreased by 68% (p<0.05) and their severity by 53% (p<0.05).

CONCLUSION

Chronic stimulation in the anteromedial GPi shows that this is a safe and effective treatment for advanced Parkinson's disease with benefit sustained for at least 6 months.

Bilateral subthalamic or pallidal stimulation for Parkinson's disease affects neither memory nor executive functions: a consecutive series of 62 patients

There is a renewal of interest in surgical approaches including lesions and deep brain stimulation directed at motor subcorticofrontal loops. Bilateral lesioning presents a far greater risk of adverse effects, especially cognitive impairment. Furthermore, the main advantages of the stimulation procedure over lesioning are adaptability and reversibility of effects. The aim of this study was to assess the influence of bilateral stimulation of the subthalamic nucleus or internal globus pallidus on memory and executive functions in Parkinson's disease. Sixty-two patients were assessed before and after 3 to 6 months of chronic bilateral stimulation of the subthalamic nucleus (n = 49) or internal globus pallidus (n = 13). The neuropsychological tests used were the Mattis Dementia Rating Scale, the Grober and Buschke Verbal Learning Test, the Wisconsin Card Sorting Test, category and literal fluency, graphic and motor series, the Stroop Test, and the Trail Making Test. Mood was evaluated by the Beck Depression Inventory. Only 4 of 25 cognitive variables were affected by deep brain stimulation. Under stimulation, performance improved for Parts A and B of the Trail Making Test, but there was a deterioration in literal and total lexical fluency. There was also a mild but significant improvement in mood. It may therefore be concluded that stimulation of the subthalamic nucleus or internal globus pallidus does not change the overall cognitive performance in Parkinson's disease and does not greatly affect the functioning of subcorticofrontal loops involved in cognition in humans. This relative absence of cognitive impairment in bilateral deep brain stimulation is likely because of the accurate positioning of the electrodes, allowing the effects of stimulation to be confined to sensorimotor circuits.

Core assessment program for surgical interventional therapies in Parkinson's disease (CAPSIT-PD)

In 1992 the Core Assessment Program for Intracerebral Transplantations (CAPIT) was published providing the minimal requirements for a common patient evaluation protocol. Despite the intent, the program was thought to be too laborious to carry out in large scale trials, and it also lacked evaluations of cognitive functions and quality of life. Moreover, the CAPIT was designed for neural transplantation only and has not been revised since. Since then, pallidotomy and deep brain stimulation have emerged as additional treatment modalities but there exists no common tool for evaluation of, and between, the techniques. In 1996, within the framework of NECTAR (Network for European CNS Transplantation and Restoration), a dedicated program entitled "Neurosurgical Interventions in Parkinson's Disease" (NIPD) was funded by the European Union Biomed 2 program to develop a new Core Assessment Program for Surgical Interventional Therapies in PD (CAPSIT-PD) and to establish an European registry for patients with PD subjected to functional neurosurgery. This article presents the recommendations of this new program.

Cutaneous electrosurgery in a patient with a deep brain stimulator

BACKGROUND

Deep brain stimulators are implantable devices with electrical activity used to treat certain movement disorders such as essential tremor and Parkinson's disease. Similar to implantable cardiac devices, use of electrosurgery on patients with these devices may produce adverse effects.

CASE REPORT

We describe the effects of electrosurgery on a patient with essential tremor and an implantable deep brain stimulator who required Mohs micrographic surgery to excise a basal cell carcinoma. The patient experienced immediate lancinating "electrical shock" using electrosurgery in the monopolar mode. The patient experienced no discomfort when a bipolar electrosurgical device was used or when his deep brain stimulator was "turned off." Appropriate positioning of the dispersive plate also reduced adverse effects.

CONCLUSION

Dermatologic surgeons should be aware of patients with devices implanted in the CNS with electrical activity and proceed with caution when using electrosurgery. Different approaches can be utilized to help reduce adverse effects.

Changes in quality of life following unilateral pallidal stimulation in Parkinson's disease

Twenty patients with Parkinson's disease (age range 38-70 years) completed the Sickness Impact Profile (SIP) 2 months before and 3 months after long-term high-frequency electrostimulation of the globus pallidus internus to improve clinical symptoms. The SIP provides an estimate of perceived quality of life on 12 health-status categories. Neurological assessment with the Hoehn and Yahr scale and the Unified Parkinson's Disease Rating Scale revealed a significant postoperative reduction in clinical symptomatology (p<0.001). The patients experienced a general improvement in self-reported quality of life that exceeded the purely motor and physical aspects of quality of life. The significant postoperative drop in perceived impairment of communication skills can be considered the most important subjective improvement. Longitudinal research on a larger sample of patients is necessary to evaluate the durability of the subjective improvement in quality of life after unilateral pallidal stimulation.

Cognitive outcome after unilateral pallidal stimulation in Parkinson's disease

OBJECTIVES

Chronic high frequency electrostimulation of the globus pallidus internus mimics pallidotomy and improves clinical symptoms in Parkinson's disease. The aim of this study was to investigate the cognitive consequences of unilateral deep brain stimulation.

METHODS

Twenty non-demented patients with Parkinson's disease (age range 38-70 years) were neuropsychologically assessed 2 months before and 3 months after unilateral pallidal stimulation. The cognitive assessment included measures of memory, spatial behaviour, and executive and psychomotor function. In addition to group analysis of cognitive change, a cognitive impairment index (CII) was calculated for each individual patient representing the percentage of cognitive measures that fell more than 1 SD below the mean of a corresponding normative sample.

RESULTS

Neurological assessment with the Hoehn and Yahr scale and the unified Parkinson's disease rating scale disclosed a significant postoperative reduction in average clinical Parkinson's disease symptomatology (p<0.001). Repeated measures multivariate analysis of variance (using right/left side of stimulation as a between subjects factor) showed no significant postoperative change in cognitive performance for the total patient group (main effect of operation). The side of stimulation did not show a significant differential effect on cognitive performance (main effect of lateralisation). There was no significant operation by lateralisation interaction effect. Although the patients experienced significant motor symptom relief after pallidal stimulation, they remained mildly depressed after surgery. Analysis of the individual CII changes showed a postoperative cognitive decline in 30% of the patients. These patients were significantly older and took higher preoperative doses of levodopa than patients showing no change or a postoperative cognitive improvement.

CONCLUSIONS

Left or right pallidal stimulation for the relief of motor symptoms in Parkinson's disease seems relatively safe, although older patients and patients needing high preoperative doses of levodopa seem to be more vulnerable for cognitive decline after deep brain stimulation.

Magnetic resonance imaging-based stereotactic localization of the globus pallidus and subthalamic nucleus

OBJECTIVE

To optimize the accuracy of initial stereotactic targeting for movement disorders surgery, we performed stereotactic localization of the internal segment of the globus pallidus (GPi) and subthalamic nucleus (STN) using magnetic resonance imaging protocols in which the borders of these nuclei were directly visualized.

METHODS

Fifty-one consecutive cases using the pallidal target and six using the subthalamic target were studied. Localization of these nuclei was performed using the Leksell stereotactic head frame and inversion recovery sequences (GPi) or T2-weighted spin echo sequences (STN). Targeting accuracy and individual variation in the spatial coordinates of these structures were independently measured by identification of nuclear boundaries during multiple microelectrode penetrations.

RESULTS

The lateral and vertical coordinates of an atlas-defined point in the GPi, with respect to the line between the anterior and posterior commissures, was highly variable. Initial targeting the GPi based on direct visualization of the target boundaries (external medullary lamina and optic tract) resulted in greater precision than would be expected using fixed anterior and posterior commissure-based coordinates. Initial targeting the STN using magnetic resonance imaging was sufficiently precise to place the initial microelectrode penetration within STN in all six cases.

CONCLUSION

Magnetic resonance imaging-based initial stereotactic targeting of the GPi, based on direct visualization of the target boundaries, is useful to improve target accuracy over that of purely indirect anterior and posterior commissure-based targeting methods. Initial targeting of the STN was reliably accomplished by direct visualization. However, there remains sufficient variability that the final target location in both GPi and STN required electrophysiological mapping in all cases.

Unilateral radiofrequency lesion versus electrostimulation of posteroventral pallidum: a prospective randomized comparison

Microelectrode-guided posteroventral pallidotomy (PVP) has shown to be an effective method in the treatment of a group of patients with advanced Parkinson's disease. A nonlesioning approach by means of deep brain electrodes connected to a programmable neuropacemaker has also been used to inhibit the internal segment of globus pallidus (posteroventral stimulation [PVS]) reporting comparable clinical efficacy to the one obtained with the ablative method. Nevertheless, no controlled studies have been performed to compare the efficacy of both procedures. A prospective series of 13 patients with a clinical indication for globus pallidus surgery was randomized either to a pallidotomy or stimulator implantation, and comparisons on motor and neuropsychologic measurements were made on a 3-month follow-up basis. Primary measurements of efficacy showed a comparable effect on Unified Parkinson's Disease Rating Scale and activities of daily living score after both procedures. Secondary measurements of efficacy showed that although both techniques improve hand tapping score and dyskinesia score, the bilateral improvement in the former was greater after PVS whereas the latter improved more significantly after PVP. No significant changes in neuropsychologic parameters were observed after either PVP or PVS. Side effects and surgery complications occurred in six of 13 patients (three after PVP and three after PVS): they were mild, transient, and unrelated to optic tract injury. In conclusion, the short-time effect and safety of both procedures is comparable.

Ablative surgery and deep brain stimulation for Parkinson's disease

Surgical options for Parkinson's disease (PD) are rapidly expanding and include ablative procedures, deep brain stimulation, and cell transplantation. The target nuclei for ablative surgery and deep brain stimulation are the motor thalamus, the globus pallidus, and the subthalamic nucleus. Multiple factors have led to the resurgence of interest in the surgical treatment of PD: 1) recognition that long-term medical therapy for PD is often unsatisfactory, with patients eventually suffering from drug-induced dyskinesias, motor fluctuations, and variable responses to medication; 2) greater understanding of the pathophysiology of PD, providing a better scientific rationale for some previously developed procedures and suggesting new targets; and 3) use of improved techniques, such as computed tomography- and magnetic resonance imaging-guided stereotaxy and single-unit microelectrode recording, making surgical intervention in the basal ganglia more precise. We review the present status of ablative surgery and deep brain stimulation for PD, including theoretical aspects, surgical techniques, and clinical results.

Chronic electrical stimulation of the left ventrointermediate (Vim) thalamic nucleus for the treatment of pharmacotherapy-resistant Parkinson's disease: a differential impact on access to semantic and episodic memory?

Thalamotomy for medically refractory Parkinson's disease (PD) is considered to be efficacious and relatively safe. Because a minority of patients experience decrements in language and memory (often mild and transient) after thalamotomy, chronic thalamic deep brain stimulation (DBS) might be a safer treatment given its reversibility and the modifiability of stimulation parameters. Two preliminary studies support the relative cognitive safety of unilateral DBS of the ventral intermediate (Vim) thalamic nucleus, but it is unclear whether possibly subtle changes in language and memory represent effects of "microthalamotomy" or of stimulation per se. This report provides preliminary data concerning effects of left thalamic stimulation on information processing speed, semantic memory (verbal fluency and visual confrontation naming), and verbal episodic memory in a patient with PD. In addition to being evaluated before and 3 and 6 months after surgery, the patient was tested 18 months after surgery either on or off medications and with the stimulator turned either on or off (order counterbalanced across medication conditions). Test performance differences between the stimulation conditions were attenuated "off" as compared to "on" medication. Vim stimulation consistently, albeit subtly, improved semantic verbal fluency but interfered with immediate recall of word lists. Parallels to findings from acute, intraoperative thalamic stimulation studies are explored. The hypothesis is offered that left Vim stimulation might facilitate access to semantic memory, but interfere with episodic memory processes.

Pallidal stimulation: an alternative to pallidotomy?

A resurgence of interest in the surgical treatment of Parkinson's disease (PD) came with the rediscovery of posteroventral pallidotomy by Laitinen in 1985. Laitinen's procedure improved most symptoms in drug-resistant PD, which engendered wide interest in the neurosurgical community. Another lesioning procedure, ventrolateral thalamotomy, has become a powerful alternative to stimulate the nucleus ventralis intermedius, producing high long-term success rates and low morbidity rates. Pallidal stimulation has not met with the same success. According to the literature pallidotomy improves the "on" symptoms of PD, such as dyskinesias, as well as the "off" symptoms, such as rigidity, bradykinesia, and on-off fluctuations. Pallidal stimulation improves bradykinesia and rigidity to a minor extent; however, its strength seems to be in improving levodopa-induced dyskinesias. Stimulation often produces an improvement in the hyper- or dyskinetic upper limbs, but increases the "freezing" phenomenon in the lower limbs at the same time. Considering the small increase in the patient's independence, the high costs of bilateral implants, and the difficulty most patients experience in handling the devices, the question arises as to whether bilateral pallidal stimulation is a real alternative to pallidotomy.

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.