Stereotactic thalamotomy in tremor-dominant Parkinson's disease: an H2(15)O PET motor activation study

Thirty Years of Global Deep Brain Stimulation: "Plus ça change, plus c'est la même chose"?

BACKGROUND

The advent of deep brain stimulation (DBS) of the subthalamic nucleus (STN) for Parkinson's disease 30 years ago has ushered a global breakthrough of DBS as a universal method for therapy and research in wide areas of neurology and psychiatry. The literature of the last three decades has described numerous concepts and practices of DBS, often branded as novelties or discoveries. However, reading the contemporary publications often elicits a sense of déjà vu in relation to several methods, attributes, and practices of DBS. Here, we review various applications and techniques of the modern-era DBS and compare them with practices of the past.

SUMMARY

Compared with modern literature, publications of the old-era functional stereotactic neurosurgery, including old-era DBS, show that from the very beginning multidisciplinarity and teamwork were often prevalent and insisted upon, ethical concerns were recognized, brain circuitries and rational for brain targets were discussed, surgical indications were similar, closed-loop stimulation was attempted, evaluations of surgical results were debated, and controversies were common. Thus, it appears that virtually everything done today in the field of DBS bears resemblance to old-time practices, or has been done before, albeit with partly other tools and techniques. Movement disorders remain the main indications for modern DBS as was the case for lesional surgery and old-era DBS. The novelties today consist of the STN as the dominant target for DBS, the tremendous advances in computerized brain imaging, the sophistication and versatility of implantable DBS hardware, and the large potential for research.

KEY MESSAGES

Many aspects of contemporary DBS bear strong resemblance to practices of the past. The dominant clinical indications remain movement disorders with virtually the same brain targets as in the past, with one exception: the STN. Other novel brain targets - that are so far subject to DBS trials - are the pedunculopontine nucleus for gait freezing, the anteromedial internal pallidum for Gilles de la Tourette and the fornix for Alzheimer's disease. The major innovations and novelties compared to the past concern mainly the unmatched level of research activity, its high degree of sponsorship, and the outstanding advances in technology that have enabled multimodal brain imaging and the miniaturization, versatility, and sophistication of implantable hardware. The greatest benefit for patients today, compared to the past, is the higher level of precision and safety of DBS, and of all functional stereotactic neurosurgery.

The variation of functional connectivity and activity before and after thalamotomy surgery (review)

Ablation surgeries are utilized to treat certain brain disorders. Recently, these surgeries have become more prevalent using techniques such as magnetic resonance guided focused ultrasound (MRgFUS) ablation and Gamma knife thalamotomy (GKT). However, as the thalamus plays a critical role in cognitive functions, the potential impact of these surgeries on functional connectivity and cognition is a matter of concern. Various approaches have been developed to locate the target for ablation and also investigate changes in functional connectivity before and after surgery. Functional magnetic resonance imaging (fMRI) and electroencephalogram (EEG) are widely used methods for assessing changes in functional connectivity and activity in clinical research. In this Review, we summarize the use of fMRI and EEG in thalamotomy surgeries. Our analysis shows that thalamotomy surgery can result in changes in functional connectivity in motor-related, visuomotor, and default-mode networks, as detected by fMRI. EEG data also indicate a reduction in over-activities observed in the preoperative state.

Assessing the impact of MR-guided focused ultrasound thalamotomy on brain activity and connectivity in patients with essential tremor

OBJECTIVE

Although magnetic resonance-guided focused ultrasound (MRgFUS) at the ventral intermediate (VIM) thalamic nucleus is a novel and effective treatment for medication-refractory essential tremor (ET), it is unclear how the ablation lesion affects functional activity. The current study sought to evaluate the functional impact of MRgFUS thalamotomy in patients with ET, as well as to investigate the relationship between neuronal activity changes and tremor control.

METHODS

This study included 30 patients with ET who underwent MRgFUS thalamotomy with a 6-month follow-up involving MRI and clinical tremor rating. Additional sex- and age-matched healthy people were recruited for the healthy control group. The fractional amplitude of low-frequency fluctuation (fALFF) and regional homogeneity were used to identify functional alteration regions of interest (ROIs). To investigate changes after treatment, ROI- and seed-based functional connectivity (FC) analyses were performed.

RESULTS

Patients with ET had significantly increased fALFF in the right postcentral gyrus (PoCG; ROI 1), regional homogeneity in the left PoCG (ROI 2), and regional homogeneity in the right PoCG (ROI 3, cluster-level p value family-wise error [pFWE] < 0.05), which were recovered and normalized at 6 months after MRgFUS thalamotomy. FCs between ROI 2 and the right supramarginal gyrus, ROI 2 and the right superior parietal gyrus, and ROI 3 and the left precentral gyrus were also found to be increased after treatment (cluster-level pFWE < 0.05). Furthermore, changes in fALFF, regional homogeneity, and FC values were significantly correlated with tremor relief (p < 0.05). Preoperative FC strengths were found to be inversely related to the postoperative tremor control ratio (p < 0.05).

CONCLUSIONS

In patients with ET, the VIM lesion of MRgFUS thalamotomy resulted in symptom-related regional functional recovery associated with sensorimotor and attention networks. Preoperative FC strengths may reflect the postoperative tremor control ratio, implying that this metric could be a useful neuroimaging biomarker for predicting symptom relief in patients with ET following thalamotomy.

Magnetic resonance-guided focused ultrasound for the treatment of tremor

INTRODUCTION

Magnetic resonance-guided focused ultrasound (MRgFUS) is an emerging treatment for tremor and other movement disorders. An incisionless therapy, it is becoming increasingly common worldwide. However, given MRgFUS' relative novelty, there remain limited data on its benefits and adverse effects.

AREAS COVERED

We review the current state of evidence of MRgFUS for tremor, highlight its challenges, and discuss future perspectives.

EXPERT OPINION

Essential tremor (ET) has been the major indication for MRgFUS since a milestone randomized controlled trial (RCT) in 2016, with substantial evidence attesting to the efficacy and acceptable safety profile of this treatment. Patients with other tremor etiologies are also being treated with MRgFUS, with studies - including an RCT - suggesting parkinsonian tremor in particular responds well to this intervention. Additionally, targets other than the ventral intermediate nucleus, such as the subthalamic nucleus and internal segment of the globus pallidus, have been reported to improve parkinsonian symptoms beyond tremor, including rigidity and bradykinesia. Although MRgFUS is encumbered by certain unique technical challenges, it nevertheless offers significant advantages compared to alternative neurosurgical interventions for tremor. The fast-growing interest in this treatment modality will likely lead to further scientific and technological advancements that could optimize and expand its therapeutic potential.

Characterization of Parkinsonian Hand Tremor and Validation of a High-Order Tremor Estimator

Recent progress in wearable technology has made wearable tremor suppression devices (WTSDs) for Parkinson's patients a potentially viable alternative solution for tremor management. So far, in contrast to wrist and elbow tremor, finger tremors have not been studied in depth despite the huge impact that they have on a patient's daily life. In addition, more evidence has been found showing that the performance of current tremor estimators may be limited by their model order due to the multiple harmonics present in tremor. The aim of this paper is to characterize finger and wrist tremor in both the time and frequency domains, and to propose a high-order tremor estimation algorithm. Tremor magnitudes are reported in the forms of linear acceleration, angular velocity, and angular displacement. The activation of forearm flexor and extensor muscles is also investigated. The frequency analysis shows that Parkinsonian tremors produce oscillations of the hand with pronounced harmonics. At last, a high-order weighted-frequency Fourier linear combiner (WFLC)-based Kalman filter is proposed. The percentage estimation accuracy achieved from the proposed estimator is 96.3 ± 1.7%, showing average improvements of 28.5% and 48.9% over its lower-order counterpart and the WFLC. The proposed estimator shows promise for use in a WTSD.

Motor thalamus integration of cortical, cerebellar and basal ganglia information: implications for normal and parkinsonian conditions

Motor thalamus (Mthal) is implicated in the control of movement because it is strategically located between motor areas of the cerebral cortex and motor-related subcortical structures, such as the cerebellum and basal ganglia (BG). The role of BG and cerebellum in motor control has been extensively studied but how Mthal processes inputs from these two networks is unclear. Specifically, there is considerable debate about the role of BG inputs on Mthal activity. This review summarizes anatomical and physiological knowledge of the Mthal and its afferents and reviews current theories of Mthal function by discussing the impact of cortical, BG and cerebellar inputs on Mthal activity. One view is that Mthal activity in BG and cerebellar-receiving territories is primarily "driven" by glutamatergic inputs from the cortex or cerebellum, respectively, whereas BG inputs are modulatory and do not strongly determine Mthal activity. This theory is steeped in the assumption that the Mthal processes information in the same way as sensory thalamus, through interactions of modulatory inputs with a single driver input. Another view, from BG models, is that BG exert primary control on the BG-receiving Mthal so it effectively relays information from BG to cortex. We propose a new "super-integrator" theory where each Mthal territory processes multiple driver or driver-like inputs (cortex and BG, cortex and cerebellum), which are the result of considerable integrative processing. Thus, BG and cerebellar Mthal territories assimilate motivational and proprioceptive motor information previously integrated in cortico-BG and cortico-cerebellar networks, respectively, to develop sophisticated motor signals that are transmitted in parallel pathways to cortical areas for optimal generation of motor programmes. Finally, we briefly review the pathophysiological changes that occur in the BG in parkinsonism and generate testable hypotheses about how these may affect processing of inputs in the Mthal.

Behind the screen: pseudobulbar symptoms after deep brain stimulation

BACKGROUND

Thalamotomy was formerly used to treat different tremor syndromes. Nowadays, deep brain stimulation has become an established technique to treat -different movement disorders. The combination of these two stereotactic interventions is rare.

CLINICAL PRESENTATION

We present a patient in which a right-sided tremor -syndrome with an underlying pathology of combined essential tremor and Parkinsonian tremor was successfully treated initially with a left-sided thalamotomy and subsequently with -bilateral deep brain stimulation in the subthalamic nucleus.

RESULTS

Deep brain stimulation in the subthalamic nucleus resulted in hemidystonia, pathological laughing and crying, dysarthria and dysphagia, all due to dislocation of the stimulation electrodes contacting the internal capsule. After discontinuation of the high-frequency stimulation these side-effects disappeared, but were then reactivated by an LCD television in stand-by mode.

CONCLUSION

In this report we discuss the pathophysiology of pseudobulbar symptoms and pathological laughing and crying in context of thalamotomy and dislocated DBS electrodes. Furthermore, we report on the occurrence that magnetic fields in the household have an impact on deep brain stimulation, even if they are in stand-by mode.

Multi-institutional evaluation of deep brain stimulation targeting using probabilistic connectivity-based thalamic segmentation

OBJECT

Due to the lack of internal anatomical detail with traditional MR imaging, preoperative stereotactic planning for the treatment of tremor usually relies on indirect targeting based on atlas-derived coordinates. The object of this study was to preliminarily investigate the role of probabilistic tractography-based thalamic segmentation for deep brain stimulation (DBS) targeting for the treatment of tremor.

METHODS

Six patients undergoing bilateral implantation of DBS electrodes in the thalamus for the treatment of upper-extremity tremor were studied. All patients underwent stereotactic surgical implantation using traditional methods (based on indirect targeting methodologies and intraoperative macrostimulation findings) that were programmed for optimal efficacy, independent of tractography-based segmentations described in this report. Connectivity-based thalamic segmentations were derived by identifying with which of 7 cortical target regions each thalamic voxel had the highest probability of connectivity. The authors retrospectively analyzed the location of the optimal contact for treatment of tremor with connectivity-based thalamic segmentations. Findings from one institution (David Geffen School of Medicine at UCLA) were validated with results from 4 patients at another institution (University of Virginia Health System).

RESULTS

Of 12 electrodes implanted using traditional methodologies, all but one resulted in efficacious tremor control. Connectivity-based thalamic segmentation consistently revealed discrete thalamic regions having unique connectivity patterns with distinct cortical regions. Although the authors initially hypothesized that the most efficacious DBS contact for controlling tremor would colocalize with the thalamic region most highly connected with the primary motor cortex, they instead found it to highly colocalize with those thalamic voxels demonstrating a high probability of connectivity with premotor cortex (center-to-center distance: 0.36 ± 0.55 mm). In contrast to the high degree of colocalization with optimal stimulation site, the precise localization of the premotor cortex-defined thalamic region relative to the anterior and posterior commissures was highly variable. Having defined a connectivity-based target for thalamic stimulation in a cohort of patients at David Geffen School of Medicine at UCLA, the authors validated findings in 4 patients (5 electrodes) who underwent surgery at a different institution (University of Virginia Health System) by a different surgeon.

CONCLUSIONS

This report identifies and provides preliminary external validation of a novel means of targeting a patient-specific therapeutic thalamic target for the treatment of tremor based on individualized analysis of thalamic connectivity patterns. This novel thalamic targeting approach is based on identifying the thalamic region with the highest probability of connectivity with premotor and supplementary motor cortices. This approach may prove to be advantageous over traditional preoperative methods of indirect targeting, providing patient-specific targets that could improve the precision, efficacy, and efficiency of deep brain stimulation surgery. Prospective evaluation and development of methodologies to make these analyses more widely available to neurosurgeons are likely warranted.

Parkinson's disease tremor-related metabolic network: characterization, progression, and treatment effects

The circuit changes that mediate parkinsonian tremor, while likely differing from those underlying akinesia and rigidity, are not precisely known. In this study, to identify a specific metabolic brain network associated with this disease manifestation, we used FDG PET to scan nine tremor dominant Parkinson's disease (PD) patients at baseline and during ventral intermediate (Vim) thalamic nucleus deep brain stimulation (DBS). Ordinal trends canonical variates analysis (OrT/CVA) was performed on the within-subject scan data to detect a significant spatial covariance pattern with consistent changes in subject expression during stimulation-mediated tremor suppression. The metabolic pattern was characterized by covarying increases in the activity of the cerebellum/dentate nucleus and primary motor cortex, and, to a less degree, the caudate/putamen. Vim stimulation resulted in consistent reductions in pattern expression (p<0.005, permutation test). In the absence of stimulation, pattern expression values (subject scores) correlated significantly (r=0.85, p<0.02) with concurrent accelerometric measurements of tremor amplitude. To validate this spatial covariance pattern as an objective network biomarker of PD tremor, we prospectively quantified its expression on an individual subject basis in independent PD populations. The resulting subject scores for this PD tremor-related pattern (PDTP) were found to exhibit: (1) excellent test-retest reproducibility (p<0.0001); (2) significant correlation with independent clinical ratings of tremor (r=0.54, p<0.001) but not akinesia-rigidity; and (3) significant elevations (p<0.02) in tremor dominant relative to atremulous PD patients. Following validation, we assessed the natural history of PDTP expression in early stage patients scanned longitudinally with FDG PET over a 4-year interval. Significant increases in PDTP expression (p<0.01) were evident in this cohort over time; rate of progression, however, was slower than for the PD-related akinesia/rigidity pattern (PDRP). We also determined whether PDTP expression is modulated by interventions specifically directed at parkinsonian tremor. While Vim DBS was associated with changes in PDTP (p<0.001) but not PDRP expression, subthalamic nucleus (STN) DBS reduced the activity of both networks (p<0.05). PDTP expression was suppressed more by Vim than by STN stimulation (p<0.05). These findings suggest that parkinsonian tremor is mediated by a distinct metabolic network involving primarily cerebello-thalamo-cortical pathways. Indeed, effective treatment of this symptom is associated with significant reduction in PDTP expression. Quantification of treatment-mediated changes in both PDTP and PDRP scores can provide an objective means of evaluating the differential effects of novel antiparkinsonian interventions on the different motor features of the disorder.

Effect of ventralis intermedius thalamotomy on the area in the sensorimotor cortex activated by passive hand movements: fMR imaging study

Stereotactic ventralis intermedius (Vim) thalamotomy is effective for essential tremor (ET) of the limb, but the effect on the activity of the sensorimotor cortex is still unclear. The functional changes in this cortical area of patients with ET after Vim thalamotomy were investigated using functional magnetic resonance (fMR) imaging. Six patients underwent Vim thalamotomy for medically intractable ET, predominantly in the right hand. 1.5-tesla fMR imaging was performed using the blood oxygenation level-dependent sequence, before and after Vim thalamotomy, during passive movements with right wrist flexion and extension. Before and after images were analyzed using SPM99 software. Activation in the sensorimotor cortex and supplementary motor area evoked by wrist passive movement was observed both before and after surgery. Group analysis of changes in the blood oxygenation level-dependent response revealed a significantly smaller activated area postoperatively. Activation at the fundus of the central sulcus was characteristically decreased. All patients showed marked improvement in tremor after Vim thalamotomy. No patient experienced neurological deficits. fMR imaging showed that activation at the fundus of the central sulcus evoked by passive wrist movement was suppressed after Vim thalamotomy in ET patients, probably due to disruption of the thalamocortical pathway. The fundus of the central sulcus (Brodmann area 3a) is likely to be one of the key relays in the tremor circuit.

The impact of ventrolateral thalamotomy on tremor and voluntary motor behavior in patients with Parkinson’s disease

A preferred target for parkinsonian tremor alleviation is the ventrolateral (VL) thalamus. The goal of the present study is to determine how lesions involving the presumed cerebellar and pallidal recipient areas of the "motor" thalamus would alter the tremor and motor behavior of ten patients with Parkinson's disease (PD). Tremor amplitude, power dispersion (a measure of sharpness of the power spectrum of tremor), and power distribution were quantified using a laser displacement sensor prior to, and a week after, VL thalamotomy. As well, the impact of surgery on tremor seen during movement was quantified in a manual-tracking (MT) task. Tremor-induced noise (a measure of the amount of tremor present during movement) and ERROR (difference between subject's performance and target) were quantified. Finally, bradykinesia was assessed with a rapid alternating movement (RAM) task. Duration, range, and amplitude irregularity of wrist pronation-supination cycles were computed. Both motor tasks were quantified using a highly sensitive forearm rotational sensor. Healthy age-matched control subjects were also tested. Magnetic resonance images with an integrated atlas of thalamic nuclei were used to confirm lesion location. Results show that the lesions were centered upon the posterior portion of the ventral lateral (VLp) nucleus of the thalamus, included the posterior part of the ventral lateral anterior nucleus (VLa), and extended posteriorly to encroach upon the most rostral sector of the sensory ventral posterior nucleus (VPLa). VL thalamotomy significantly decreased tremor amplitude in all cases. Power dispersion was increased significantly so that it became similar to that of control subjects. Changes in power distribution indicate that thalamotomy selectively targeted PD tremor oscillations. Tremor detected during the MT task was also markedly decreased, becoming similar to that of controls. Patients also showed significant decrease in ERROR during MT. RAM duration and range were not significantly modified by the surgery, and patients' performance remained impaired compared to healthy control subjects. Collectively, these results suggest that lesions involving the presumed "cerebellar" and "pallidal" recipient sectors of the motor thalamus do not worsen bradykinesia, suggesting that neural circuits other than the pallido-thalamo-cortical loop may be involved in slowness of movement in PD. A review of alternate pathways is presented.

The impact of ventrolateral thalamotomy on high-frequency components of tremor

OBJECTIVE

The present study assessed the impact of ventrolateral (VL) thalamotomy on the high-frequency components of tremor in patients with Parkinson's disease (PD).

METHODS

Tremor was recorded prior to, and 7 days post-surgery using a laser displacement sensor. In addition, tremor was recorded in 10 age-matched patients with PD showing low amplitude tremor (named PD controls) and in 10 age-matched control subjects. Tremor recordings in patients were performed after a 12h withdrawal from anti-Parkinsonian drugs. Tremor characteristics such as amplitude, median power frequency (MPF) and power dispersion (a measure of concentration of power in the frequency domain) were assessed for all groups (i.e. controls, PD controls, pre-surgery and post-surgery).

RESULTS

All tremor characteristics were similar between controls and PD controls. Tremor amplitude was significantly reduced post-surgery, to become statistically similar to that of controls and PD controls. However, MPF and power dispersion remained lower post-surgery, indicating that although there was normalization of tremor amplitude, tremor showed systematically slower oscillations after the surgical procedure. In order to eliminate amplitude as a possible confounding factor, epochs of post-surgical tremor (5s in duration) were paired for equal amplitude with 5s tremor epochs from matched controls. Results show once again that MPF and power dispersion were lower post-surgery compared to controls. In addition, when amplitude of power was compared within specific frequency bands (0-3.5, 3.5-7.5, 7.5-12.5, 12.5-16.5, 16.5-30 and 30-45), power regained normal values at frequencies below 7.5 Hz. Power within higher frequency bands was systematically lower, indicating that the surgical procedure had an impact on high-frequency components of tremor.

CONCLUSIONS

Results from the present study showed that VL thalamotomy reduced tremor amplitude by selectively targeting centrally driven components of PD tremor. The high-frequency component of physiological tremor failed to emerge after amplitude normalization.

SIGNIFICANCE

The thalamus should then be considered as an important component of the generation and/or propagation of high-frequency components of physiological tremor.

Thalamic stimulation for parkinsonian tremor: correlation between regional cerebral blood flow and physiological tremor characteristics

We used (15)O-labeled water (H(2)(15)O) positron emission tomography (PET) to study eight Parkinson's disease (PD) patients with unilateral ventral intermediate (Vim) thalamic nucleus deep brain stimulation (DBS) for severe tremor. Triaxial accelerometry (TRIAX) was used during imaging to obtain on-line measures of tremor characteristics. Regional cerebral blood flow (rCBF) scans together with TRIAX recordings were collected in three stimulation conditions (OFF, MID, and ON, corresponding, respectively, to 0%, 50%, and 100% reductions in mean accelerometry signal). Statistical Parametric Mapping (SPM99) revealed significant rCBF reductions during stimulation in the ipsilateral sensorimotor cortex (SMC) and the contralateral cerebellum, as well as concurrent increases in the ipsilateral ventral thalamus (P < 0.05, corrected). Covariate analysis of rCBF with physiological tremor characteristics revealed that tremor acceleration correlated positively with changes in the SMC and supplementary motor cortex ipsilaterally (P < 0.05, uncorrected), and negatively with changes in the ipsilateral cuneus (P < 0.05, corrected). After removing tremor acceleration effects, changes in tremor frequency correlated negatively with changes in the contralateral dentate nucleus and pons (P < 0.05, uncorrected). Our results suggest that Vim DBS for PD tremor modulates the activity of cerebello-thalamo-cortical pathways. Specific tremor characteristics relate to activity in different nodes of this system.

Chapter 78 How does DBS work?

Deep brain stimulation (DBS) produces striking effects in patients with various disorders including Parkinson's disease and dystonia, yet its precise mechanism of action is not clear. Because the clinical benefits of lesioning target structures such as the thalamus, globus pallidus and subthalamic nucleus appear to be similar to those achieved by chronic application of stimulation at these structures, it has been surmized that deep brain stimulation produces a functional inactivation or block of the target. This simplistic proposal has supporting and detracting evidence. In the present work we consider the mechanism of action of DBS and provide arguments for and against the stimulation or inhibition of target neural structures.

Tremor in Parkinson's disease

Rest tremor is a common feature of Parkinson's disease, but its underlying pathophysiology remains unknown. This review hypothesizes that tremor is related to selective loss of components of the substantia nigra. The relative scarcity of tremor in related Parkinsonian conditions may indicate a dissociation associated with different pathological involvement of the substantia nigra and its connections. Connections of the subthalamic nucleus with the pallidum, modified by cortical and nigral inputs, allow for the transfer of tremorogenic activity to the thalamus. Thalamo-cortical interactions, tempered by cerebellar input, generate the final common pathway for tremor production.

Deactivation of thalamocortical activity is responsible for suppression of parkinsonian tremor by thalamic stimulation: a 99mTc-ECD SPECT study

Four patients with Parkinson's disease (PD) achieved excellent improvement of their unilateral tremor by chronic deep brain stimulation (DBS) of the contralateral ventral intermediate (Vim) nucleus of the thalamus. Repeated measurements of cerebral blood flow were obtained 14 days apart off and on stimulation using 99mTc-ECD SPECT. Subjects were scanned at rest and the data were compared with those of normal healthy volunteers. During stimulation, there were highly significant deactivations in the motor area and supplementary motor area on the electrode side and in the prefrontal area and the anterior cingulum bilaterally. No cerebellar deactivation was detected. We conclude that the mechanism responsible for suppression of parkinsonian tremor by thalamic stimulation is deactivation of thalamocortical activity.

Gamma knife thalamotomy for treatment of tremor: long-term results

Object. The purpose of this study was to investigate the long-term effects of gamma knife thalamotomy for treatment of disabling tremor.

Methods. One hundred fifty-eight patients underwent magnetic resonance imaging—guided radiosurgical nucleus ventralis intermedius (VIM) thalamotomy for the treatment of parkinsonian tremor (102 patients), essential tremor (52 patients), or tremor due to stroke, encephalitis, or cerebral trauma (four patients). Preoperative and postoperative blinded assessments were performed by a team of independent examiners skilled in the evolution of movement disorders. A single isocenter exposure with the 4-mm collimator helmet of the Leksell gamma knife unit was used to make the lesions.

In patients with Parkinson's disease 88.3% became fully or nearly tremor free, with a mean follow up of 52.5 months. Statistically significant improvements were seen in Unified Parkinson's Disease Rating Scale tremor scores and rigidity scores, and these improvements were maintained in 74 patients followed 4 years or longer.

In patients with essential tremor, 92.1% were fully or nearly tremor free postoperatively, but only 88.2% remained tremor free by 4 years or more post-GKS. Statistically significant improvements were seen in the Clinical Rating Scale for tremor in essential tremor patients and these improvements were well maintained in the 17 patients, followed 4 years or longer. Only 50% of patients with tremor of other origins improved significantly.

One patient sustained a transient complication and two patients sustained mild permanent side effects from the treatments.

Conclusions. Gamma knife VIM thalamotomy provides relief from tremor equivalent to that provided by radiofrequency thalamotomy or deep brain stimulation, but it is safer than either of these alternatives. Long-term follow up indicates that relief of tremor is well maintained. No long-term radiation-induced complications have been observed.

Acute effects of thalamotomy and pallidotomy on regional cerebral metabolism, evaluated by PET

The subacute effect of thalamotomy and pallidotomy on regional cerebral metabolism was studied by means of Positron Emission Tomography (PET). In this way we aimed to identify the pattern of functional deafferentiation following a specific lesion in the basal ganglia. The cerebral distribution of 2-[18F]fluoro 2-deoxy-D-glucose (FDG) uptake at 1-2 weeks after operation was compared with the uptake before operation. Analysis of the changes was done by statistical parametric mapping (SPM). Thalamotomy resulted in a reduction of FDG uptake in predominantly the lateral prefrontal- and the parietal cortex, whereas pallidotomy affected only uptake in the (pre)frontal cortex. The absence of change in the primary sensory-motor cortex after either surgical procedure may suggest that, in man, the motor portions of the thalamus exert a predominantly indirect influence on the human motor cortex.

Cognitive outcomes after deep brain stimulation for Parkinson's disease: a review of initial studies and recommendations for future research

Modern ablative surgery for movement disorders probably results in less frequent and severe cognitive morbidity than seen in early surgical series. Nonetheless, recent studies indicate that neurobehavioral functions commonly compromised in Parkinson's disease (PD) (e.g., executive functions, verbal fluency, and memory) are negatively impacted in some patients by lesion placement. The potential reversibility of cognitive dysfunction after chronic electrical deep brain stimulation (DBS) for PD has lead some to favor this treatment modality over ablation. This paper reviews the initial studies of the cognitive effects of thalamic, pallidal, and subthalamic DBS. These studies suggest that DBS is relatively safe from a cognitive standpoint and that the benefits of motor improvements probably outweigh the cost of minimal cognitive morbidity. This conclusion must be offered with caution, however, given the small numbers of studies to date and their methodological limitations. Neurobehavioral research has yet to adequately address (1) outcome relative to appropriate control groups; (2) effects of electrode placement versus stimulation; (3) laterality- and site-specific effects of DBS; (4) long-term effects of DBS; (5) effects of stimulation parameters; (6) risk factors for cognitive dysfunction with DBS; (7) whether cognitive dysfunction associated with DBS is reversible; and (8) comparative neurobehavioral outcome after DBS and ablation. DBS affords an exciting opportunity to clarify the neurobehavioral role of the basal ganglia.

Post mortem studies in Parkinson's disease--is it possible to detect brain areas for specific symptoms?

Parkinson's disease (PD) is characterized by progressive neuronal loss associated with Lewy bodies in many subcortical nuclei leading to multiple biochemical and pathophysiological changes of clinical relevance. Loss of nigral neurons causing striatal dopamine deficiency is related to both the duration and clinical stages (severity) of the disease. The clinical subtypes of PD have different morphological lesion patterns: a) The akinetic-rigid type shows more severe cell loss in the ventrolateral part of substantia nigra zona compacta (SNZC) that projects to the dorsal putamen than the medial part projecting to caudate nucleus and anterior putamen, with negative correlation between SNZC cell counts, severity of akinesia-rigidity, and dopamine loss in the posterior putamen. Reduced dopaminergic input causes overactivity of the GABA ergic inhibitory striatal neurons projecting via the "indirect loop" to SN zona reticulata (SNZR) and medial pallidum (GPI) leading to inhibition of the glutamatergic thalamo-cortical motor loop and reduced cortical activation. b) The tremor-dominant type shows more severe neuron loss in medial than in lateral SNZC and damage to the retrorubral field A8 containing only few tyrosine hydroxylase and dopamine transporter immunoreactive (IR) neurons but mainly calretinin-IR cells. A8 that is rather preserved in rigid-akinetic PD (protective role of calcium-binding protein?) projects to the matrix of dorsolateral striatum and ventromedial thalamus. Together with area A10 it influences the strial efflux via SNZR to thalamus and from there to prefrontal cortex. Rest tremor in PD is associated with increased metabolism in the thalamus, subthalamus, pons, and premotor-cortical network suggesting an increased functional activity of thalamo-motor projections. In essential tremor, no significant pathomorphological changes but overactivity of cerebello-thalamic loop have been observed. c) In the akinetic-rigid forms of multisystem atrophy, degeneration is more severe in the lateral SNZC with severe loss of calbindin-IR cells reflecting initial degeneration of the striatal matrix in the caudal putamen with transsynaptic degeneration of striatonigral efferences that remain intact in PD. This fact and loss of striatal D2 receptors--as in advanced stages of PD--are reasons for negative response to L-dopa substitution. These data suggest different pathophysiological mechanisms of the clinical subtypes of PD that have important therapeutic implications. d) Involvement of extranigral structures in PD includes the mesocortical dopaminergic system, the noradrenergic locus coeruleus, dorsal vagal nucleus and medullary nuclei, serotonergic dorsal raphe, nucleus basalis of Meynert and other cholinergic brainstem nuclei, e.g. Westphal-Edinger nucleus (controlling pupillomotor function), posterolateral hypothalamus and the limbic system, e.g. amygdaloid nucleus, part of hippocampal formation, limbic thalamic nuclei with prefrontal projections, etc. Damage to multiple neuronal systems by the progressing degenerative process causing complex biochemical changes may explain the variable clinical picture of PD including vegetative, behavioural and cognitive dysfunctions, depression, pharmacotoxic psychoses, etc. Future comparative clinico-morphological and pathobiochemical studies will further elucidate the pathophysiological basis of specific clinical symptoms of PD and related disorders providing a broader basis for effective treatment strategies. Parkinson's disease (PD) is characterized by progressive degeneration of the nigrostriatal dopaminergic system and other subcortical neuronal systems leading to striatal dopamine deficiency and other biochemical deficits related to the variable clinical signs and symptoms of the disorder. (ABSTRACT TRUNCATED)

Functional imaging of Parkinson's disease: is it possible to detect brain areas for specific symptoms?

H2(15)O PET activation studies enable the brain systems involved in controlling different aspects of motor function to be defined. In Parkinson's disease (PD) freely chosen limb movements are performed slowly. This bradykinesia is associated with selective underactivity of the supplementary motor area and dorsal prefrontal cortex, frontal association areas that receive subcortical input principally from the basal ganglia. At the same time there is compensatory overactivity of the lateral premotor and parietal cortex, areas that have a primary role in facilitating motor responses to visual and auditory cues. This finding explains why PD patients find it easier to perform cued as opposed to freely chosen actions. Levels of activation of the supplementary motor area and dorsal prefrontal cortex in PD can be restored with dopaminergic medication, implants of fetal mesencephalic tissue, internal pallidotomy or high frequency electrical subthalamic stimulation. Activation studies suggest that Parkinsonian rest tremor arises from a combination of inappropriate overactivity of cerebellar connections and loss of dopaminergic function. When tremor is relieved by ventral thalamotomy or thalamic stimulation this cerebellar overactivity is corrected but at the expense of reducing levels of primary motor cortex activation. It has been hypothesised that dyskinesias in PD arise due to altered dopamine receptor binding following chronic exposure to levodopa stimulation. Functional imaging findings, however, are against this hypothesis and rather suggest that downstream increases in basal ganglia opioid neurotransmission are more likely to be relevant.

Functional imaging of tremor

We review the insight that has been obtained from positron emission tomography (PET) and magnetic resonance imaging (MRI) activation studies on the functional anatomy underlying different forms of tremor. The effects of treatment, both pharmacologic and interventional approaches, on the dysfunctional cerebral systems involved in tremor, also are considered. Finally, we speculate on the neuropharmacologic basis of different types of tremor based on available in vivo PET evidence.