Posteroventral medial pallidotomy in advanced Parkinson's disease

Unilateral stimulation of the subthalamic nucleus in Parkinson disease: a double-blind 12-month evaluation study

OBJECT

Bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been established as an effective treatment for Parkinson disease (PD). Nevertheless, bilateral surgical procedures can be associated with frequent and severe complications. The aim in the present study was to assess the safety and efficacy of unilateral STN stimulation, and the need for a second procedure.

METHODS

Twelve patients with PD underwent unilateral DBS of the STN and were followed up for 12 months. Patients were assessed at baseline and at each visit in a double-blind fashion by analyzing the Unified PD Rating Scale (UPDRS), ambulation speed, and home diaries. Levodopa-off/stimulation-on UPDRS motor scores were improved by 26 +/- 8% (p < 0.05, mean +/- standard deviation [SD]) compared with the baseline levodopa-off score; there was a 50% improvement in contralateral features, a 17% improvement ipsilaterally, and a 36% improvement in axial features. The mean ambulation speed increased by 83 +/- 44% (p < 0.01, mean +/- SD). The medication-on time with dyskinesias was significantly reduced (p < 0.01) and the daily levodopa dose was reduced by 19 +/- 6% (p < 0.05, mean +/- SD). There were no clinically significant side effects.

CONCLUSIONS

Unilateral DBS of the STN is safe and well tolerated, and may provide sufficient benefit so that additional surgery is not required.

Levodopa in the treatment of Parkinson's disease: Current controversies

Levodopa is the most effective symptomatic agent in the treatment of Parkinson's disease (PD) and the "gold standard" against which new agents must be compared. However, there remain two areas of controversy: (1) whether levodopa is toxic, and (2) whether levodopa directly causes motor complications. Levodopa is toxic to cultured dopamine neurons, and this may be a problem in PD where there is evidence of oxidative stress in the nigra. However, there is little firm evidence to suggest that levodopa is toxic in vivo or in PD. Clinical trials have not clarified this situation. Levodopa is also associated with motor complications. Increasing evidence suggests that they are related, at least in part, to the short half-life of the drug (and its potential to induce pulsatile stimulation of dopamine receptors) rather than to specific properties of the molecule. Treatment strategies that provide more continuous stimulation of dopamine receptors provide reduced motor complications in MPTP monkeys and PD patients. These studies raise the possibility that more continuous and physiological delivery of levodopa might reduce the risk of motor complications. Clinical trials to test this hypothesis are underway. We review current evidence relating to these areas of controversy.

Treatments for dysarthria in Parkinson's disease

Dysarthria in Parkinson's disease can be characterised by monotony of pitch and loudness, reduced stress, variable rate, imprecise consonants, and a breathy and harsh voice. Use of levodopa to replenish dopamine concentrations in the striatum seems to improve articulation, voice quality, and pitch variation, although some studies show no change in phonatory parameters. Traditional speech therapy can lead to improvement of dysarthria, and intensive programmes have had substantial beneficial effects on vocal loudness. Unilateral surgical lesions of subcortical structures are variably effective for the alleviation of dysarthria, whereas bilateral procedures typically lead to worsening of speech production. Among deep-brain stimulation procedures, only stimulation of the subthalamic nucleus improves some motor components of speech although intelligibility seems to decrease after surgery. Due to the variable treatment effects on parkinsonian speech, management of dysarthria is still challenging for the clinician and should be discussed with the patient.

Effects of stereotactic neurosurgery on postural instability and gait in Parkinson's disease

Postural instability and gait disability (PIGD) are disabling signs of Parkinson's disease. Stereotactic surgery aimed at the internal globus pallidus (GPi) or subthalamic nucleus (STN) might improve PIGD, but the precise effects remain unclear. We performed a systematic review of studies that examined the effects of GPi or STN surgery on PIGD. Most studies examined the effects of bilateral GPi stimulation, bilateral STN stimulation, and unilateral pallidotomy; we, therefore, only performed a meta-analysis on these studies. Bilateral GPi stimulation, bilateral STN stimulation, and to a lesser extent, unilateral pallidotomy significantly improved PIGD, and more so during the ON phase than during the OFF phase.

Deep brain stimulation for hyperkinetic disorders

Deep brain stimulation (DBS) has a record of safety and efficacy for an expanding range of indications. Recently, the Food and Drug Administration provided approval through a Humanitarian Device Exemption for DBS of the globus pallidus internus and subthalamic nucleus for the treatment of dystonia. There is increasing clinical experience demonstrating that DBS is also effective for other hyperkinetic disorders such as chorea from a variety of causes. The selection criteria, intraoperative targeting, and the postoperative management of DBS for hyperkinetic disorders are discussed.

Hand rhythmic tapping and timing in Parkinson's disease

BACKGROUND

Dysrhythmia is one of the features frequently associated with the motor disturbance in Parkinson's disease (PD). The mechanism responsible for this phenomenon is not known.

OBJECTIVES

To assess the rhythmic movements of the hand in PD patients in general and in parkinsonian subtypes.

METHODS

Fifty-one PD patients (32 males) with mean age 66.3 +/- 9.1 years (6.6 years of symptoms) and 36 healthy controls (age 64.9 +/- 13.2, range 40-85) were studied. Subjects were asked to tap with their dominant or less affected arm on a digitized switch board at their most comfortable pace (16 s), fastest tapping speed (12 s), and at different frequencies provided by a metronome. The mean rhythm and the tap-to-tap variation were compared. Performance of the PD patients and control subjects were compared, as there were different subtypes of PD patients. Patients were subclassified into: tremor predominant (TP) (14 patients), freezing predominant (FP) (11 patients), akinetic-rigid (AR) (12 patients) and an unclassified group (UC) (14 patients). Results. There was no significance difference between patients and controls in the self-chosen, most comfortable tapping rate or in the tap-to-tap variation of the self-paced task. PD patients tapped at a significantly slower rate than controls when asked to tap at their fastest rate (4.39 +/- 1.32 vs. 5.14 +/- 1.31 Hz; p < 0.01). This difference was the result of an especially slow performance of the TP and AR subgroups (3.85+/-1.20 and 3.88+/-1.46, respectively; p < 0.01 compared to the control group). TP was the only subgroup to show an increased tap-to-tap variation at their fastest tapping rate compared to the control group (0.070 +/- 0.057 vs. 0.029 +/- 0.025 s, respectively, p < 0.05). The TP subgroup also showed hastening when they followed an externally given rhythm of 2.5 Hz and they tapped at 2.73 +/- 0.36 Hz p < 0.05).

CONCLUSIONS

Externally driven and self-paced tapping are preserved in patients with PD, when examined at their best 'on' state. The tremor predominant subgroup seems to have specific pacing disturbances.

Variability in position of the subthalamic nucleus targeted by magnetic resonance imaging and microelectrode recordings as compared to atlas co-ordinates

BACKGROUND

Traditional methods for localisation of target nuclei for deep brain stimulation (DBS) have used brain atlas co-ordinates for initial targeting. It is now possible to visualise the subthalamic nucleus (STN) on magnetic resonance imaging (MRI) and determine the individual variability of its position.

METHODS

The present study was performed in patients undergoing STN DBS for Parkinson's disease. The STN was directly targeted from axially obtained MRI and verified with microelectrode recordings. Postoperatively, the most effective contact was identified for each patient, and its position was calculated.

RESULTS

Fifty electrodes were inserted in 25 patients. The target position varied considerably in relation to the mid-commissural point. The mean effective contact position lies just dorsal to the location of the STN in a standard brain atlas.

CONCLUSION

The STN varies in position, and can be accurately targeted from MRI alone.

Lesion therapy for Parkinson's disease and other movement disorders: Update and controversies

An analysis of the international literature on lesioning for movement disorders was undertaken to review lesion therapy for Parkinson's disease (PD) and other movement disorders and to highlight important controversies surrounding this surgical technique. Lesions have been placed throughout the neuraxis with varying approaches and success. Our understanding of the pathophysiological basis underlying the development of PD and other movement disorders has led to a better understanding of why lesioning certain portions of the nervous system should improve motor function. Advances in imaging technology and electrophysiological techniques used for localization of brain structures, such as microelectrode mapping, have improved the ability to accurately identify and lesion target structures deep in the brain. This improvement has led to an increase in the degree and consistency of clinical benefit. The major controversies in lesion therapy include: (1) which target for which disorder; (2) determination of the optimal lesion site and whether the external globus pallidus (GPe) should be included in the pallidotomy lesion for PD; (3) determination of the size of the lesion; (4) whether bilateral lesions can be placed without the high incidence of side effects reported by some investigators; (5) whether microelectrodes aid in the ability to improve clinical outcomes or increase the risk of side effects by making multiple microelectrode penetrations; (6) whether the subthalamic nucleus (STN) should be explored further as a lesioning target; and (7) whether lesioning should be abandoned entirely in favor of deep brain stimulation (DBS). Many important questions and controversies regarding lesion therapy remain unanswered. It is unlikely given the pro-DBS environment that these questions will be answered in the near future. We should, however, be careful not to abandon an effective therapy before fully exploring through randomized trials the relative effect of different surgical approaches for the treatment of patients with movement disorders.

The Scientific Basis for the Current Treatment of Parkinson's Disease

Parkinson's disease (PD) is an age-related neurodegenerative disease that affects approximately one million people in the United States. The introduction of levodopa revolutionized the treatment for this disorder, but the long-term utility of the drug is limited by motor complications, the development of features such as postural instability and dementia that do not respond to treatment, and continued disease progression. Insights into the organization of the basal ganglia in the normal and PD conditions has permitted the design of new treatment strategies that reduce the risk of developing motor complications. Additionally, increased knowledge of the mechanisms responsible for cell death in PD has permitted the development of putative neuroprotective drugs that might slow or stop disease progression. No drug has yet been established to alter the rate of disease progression, but the rapid pace of research offers reason for optimism.

Dopaminergic Hypersensitivity In Patients With Parkinson Disease And Migraine

Because migraine has been associated with dopaminergic receptor hypersensitivity, the authors hypothesized that patients with Parkinson disease with current or prior migraine have better dopaminergic response and less motor disability than Parkinson disease patients without migraine. Twenty-eight patients with Parkinson disease were included and matched (10 patients with migraine and 18 patients without migraine). Patients with Parkinson disease and migraine showed greater motor improvement during the ON state than patients without migraine with the same medication exposure. These data support the hypothesis that migraine may be associated with dopaminergic hypersensitivity.

Subthalamic nucleus deep brain stimulation for parkinson's disease after successful pallidotomy: Clinical and electrophysiological observations

Unilateral pallidotomy is an effective treatment for contralateral parkinsonism and dyskinesia, yet symptoms progress in many patients. Little is known about whether such patients obtain a useful response to subsequent bilateral subthalamic nucleus deep brain stimulation (STN DBS). Changes in Unified Parkinson's Disease Rating Scale (UPDRS) Motor and Activities of Daily Living (ADL) scores, medication requirements, and dyskinesias were measured. Clinical outcomes were compared to patients with de novo STN DBS. Neuronal recordings were performed. STN DBS resulted in a significant reduction in UPDRS Motor scores (42.1%; 95% confidence interval [CI], 26.9-57.4; P = 0.03), comparable with de novo STN DBS surgery (41%; 95% CI, 26-46%; P < 0.001). There was also less change in dyskinesia duration and disability scores (P = 0.017, 0.005). There were no side-to-side differences clinically or in the STN neuronal firing rates and patterns. Bilateral STN DBS is safe and efficacious in improving motor symptoms in patients with prior pallidotomy.

Bilateral globus pallidus stimulation for Huntington's disease

Bilateral globus pallidus internus (GPi) deep brain stimulation (DBS) was performed in a patient with Huntington's disease (HD) with severe chorea. Stimulation at 40 and 130 Hz improved chorea. Stimulation at 130 Hz slightly worsened bradykinesia overall, whereas 40 Hz had little effect. A [15O] H2O positron emission tomography showed increased regional cerebral blood flow in motor decision making and execution areas more evident at 40 Hz. Adjustment of stimulation parameters in GPi DBS may have the potential to optimize the motor response in HD, improving chorea without aggravating bradykinesia.

Static balance impairment and its change after pallidotomy in Parkinson's disease

We compared postural sway parameters during a 1-minute quiet stance in 28 patients with idiopathic Parkinson's disease (PD) in off phase with those in 17 age-matched normal subjects and investigated differences in the sway parameters before and after unilateral pallidotomy in 16 PD patients. The PD patients showed larger sway area (SA) and longer total sway path length (SPL) compared with normal subjects. Total SPL after subtraction of tremor effect did not differ from that in normal subjects. The shift of the mean center of foot pressure (CFP) position from the first 30 seconds to the last 30 seconds showed that the CFP tended to move forward in PD patients compared with normal subjects and to move laterally more in PD patients than normal subjects, especially in those with less severity (Unified Parkinson's Disease Rating Scale, motor score < 40). After the operation, there was little change in either SA or lateral movement of CFP, but forward movement of CFP and total SPL tended to be normalized, along with an improvement of major parkinsonian symptoms. From these results, it is concluded that SPL elongation significantly involves tremor effect, forward movement of CFP in PD derives from basal ganglia dysfunction, and SA enlargement and large lateral movement of CFP may be caused partly by compensatory movements or by dysfunction outside the basal ganglia circuitry.

Surgery for Parkinson disease in the United States, 1996 to 2000: practice patterns, short-term outcomes, and hospital charges in a nationwide sample

Object. The surgical treatment of Parkinson disease (PD) has undergone a dramatic shift, from stereotactic ablative procedures toward deep brain stimulaion (DBS). The authors studied this process by investigating practice patterns, mortality and morbidity rates, and hospital charges as reflected in the records of a representative sample of US hospitals between 1996 and 2000.

Methods. The authors conducted a retrospective cohort study by using the Nationwide Inpatient Sample database; 1761 operations at 71 hospitals were studied. Projected to the US population, there were 1650 inpatient procedures performed for PD per year (pallidotomies, thalamotomies, and DBS), with no significant change in the annual number of procedures during the study period. The in-hospital mortality rate was 0.2%, discharge other than to home was 8.1%, and the rate of neurological complications was 1.8%, with no significant differences between procedures. In multivariate analyses, hospitals with larger annual caseloads had lower mortality rates (p = 0.002) and better outcomes at hospital discharge (p = 0.007).

Placement of deep brain stimulators comprised 0% of operations in 1996 and 88% in 2000. Factors predicting placement of these devices in analyses adjusted for year of surgery included younger age, Caucasian race, private insurance, residence in higher-income areas, hospital teaching status, and smaller annual hospital caseload. In multivariate analysis, total hospital charges were 2.2 times higher for DBS (median $36,000 compared with $12,000, p < 0.001), whereas charges were lower at higher-volume hospitals (p < 0.001).

Conclusions. Surgical treatment of PD in the US changed significantly between 1996 and 2000. Larger-volume hospitals had superior short-term outcomes and lower charges. Future studies should address long-term functional end points, cost/benefit comparisons, and inequities in access to care.

Stereotaxic intrastriatal implantation of human retinal pigment epithelial (hRPE) cells attached to gelatin microcarriers: a potential new cell therapy for Parkinson's disease

Human retinal pigment epithelial (hRPE) cells are dopaminergic support cells in the neural retina. Stereotaxic intrastriatal implantation of hRPE cells attached to gelatin microcarriers (Spheramine) in rodent and non-human primate models of Parkinson's disease (PD) produces long term amelioration of motor and behavioral deficits, with histological and PET evidence of cell survival without immunosuppression. Long-term safety in cynomologous monkeys has also been demonstrated. Six H&Y stage III/IV PD patients were enrolled in a one-year, open-label, single center study to evaluate the safety and efficacy of Spheramine (approximately 325,000 cells) implanted in the most affected post-commissural putamen. All patients tolerated the implantation of Spheramine well and demonstrated improvement. At 6, 9, and 12 months post-operatively, the mean UPDRS-Motor score "off", the primary outcome measure, improved 33%, (n = 6), 42% (n = 6), and 48% (n = 3), respectively. No "off-state" dyskinesias have been observed. Based on these preliminary results, Spheramine appears to show promise in treating late stage PD patients.

Effects of pallidotomy and levodopa on walking and reaching movements in Parkinson's disease

We examined the effects of levodopa and unilateral pallidotomy on quantitative measures of walking and reaching in Parkinson's disease (PD). We also compared quantitative measures of movement with standard clinical rating scales. We used kinematic measures and the Unified Parkinson's Disease Rating Scale (UPDRS) motor subscale (subscale III) to evaluate the movement of 10 people with PD. Subjects were tested after withholding PD medications for at least 8 hours and again 30 to 45 minutes after taking the first morning dose of levodopa. They were studied in this manner before unilateral pallidotomy and then 3.5 to 10 months after surgery. The UPDRS motor subscale was performed in each state. Kinematic data were collected as subjects reached to a target and walked. The UPDRS motor subscale ratings were similar to those reported in the literature: pallidotomy improved the overall motor score and the contralateral bradykinesia + rigidity score, but not the gait + posture score. In contrast, kinematic measures demonstrated that levodopa and pallidotomy had different effects on walking and reaching speed. Both treatments improved walking speed, and the effect was additive. Levodopa improved reaching speed before pallidotomy but did not improve it as much after pallidotomy. Additionally, pallidotomy had inconsistent effects on reaching; some subjects were faster and others were slower. The subjects who initially reached more slowly improved after pallidotomy; the subjects who initially reached more normally (faster) worsened after pallidotomy. On the basis of our results, we speculate that basal ganglia output pathways that control walking and reaching may be distinct, such that bilateral projections to the pedunculopontine area influence walking, whereas ipsilateral thalamocortical projections influence reaching.

Hemorrhagic complication of stereotactic surgery in patients with movement disorders

OBJECT

Small, asymptomatic hemorrhages are easier to detect during stereotactic surgery when magnetic resonance (MR) imaging is used for targeting rather than when traditional approaches, such as ventriculography, are performed with contrast material. In the present study the authors examined the actual incidence of intraoperative hemorrhages in patients with movement disorders who had undergone MR imaging-targeted surgery, microelectrode recording (MER)-guided implantation of deep brain stimulation (DBS) electrodes, or radiofrequency-induced coagulation surgery performed.

METHODS

Ninety-six consecutive patients underwent a total of 116 stereotactic operations for movement disorders (57 operations for radiofrequency-induced coagulation and 59 for DBS electrode implantation) between January 1998 and November 2002. The authors investigated the correlation between hemorrhages and other factors including the location of the hemorrhage and the type of surgery performed. Postoperative computerized tomography scans demonstrated the occurrence of intraoperative hemorrhages at 12 locations during 11 procedures (9.5% of all procedures). Nine hemorrhages occurred during 57 coagulation operations (15.8%). Within this group, the frequency of hemorrhages was highest during thalamotomy (five [21.7%] of 23 procedures) and lower during pallidotomy (four [11.8%] of 34 procedures). In contrast, only two intraventricular hemorrhages developed during 59 operations in which DBS electrodes were implanted (3.4%). In no case was hemorrhage detected in the main DBS target, that is, the subthalamic nucleus.

CONCLUSIONS

When small, asymptomatic hemorrhages were included in the estimation, the actual rate of hemorrhage was higher than that previously reported. Judging from the incidence of hemorrhage during coagulation and DBS surgeries, the authors suggest that the heat induced by coagulation may play a larger role than microelectrode penetration in the development of hemorrhage.

Physiology and pathophysiology of Parkinson's disease

The behavior of neurons in the basal ganglia is severely disrupted in Parkinson's disease (PD). In nonhuman parkinsonian primate models, the disturbance in neurons in basal ganglia output structures include increased firing, bursting, an augmented synchrony, correlated activity, and a tendency towards loss of specificity in their receptive fields. This abnormal neuronal behavior, transmitted to the thalamus, cortex and brainstem, is thought to disrupt the functioning of the motor system and underlie the major motor manifestations of PD-tremor, rigidity, akinesia, gait, and postural disturbances. The mainstay of treatment has been to replace the missing dopamine with medication. With time and disease progression, however, dopamine replacement becomes less efficacious and new adverse effects, including the development of motor fluctuations and drug-induced involuntary movements or dyskinesias, emerge. When the patients reach this stage, surgical therapy becomes an option. Most surgical interventions are performed at the level of the thalamus, globus pallidus, and subthalamic nucleus, aiming at the disruption of the pathological activity that accompanies the Parkinson's deficiency state. With this abnormal neuronal activity neutralized, normal movements can in many cases be restored.

Treatment of advanced Parkinson's disease by subthalamotomy: one-year results

We studied effects on parkinsonian features at 6 and 12 months in 12 patients who underwent unilateral ablation of subthalamic nucleus (STN). Microelectrode mapping was used, and a lesion was created in the STN using thermal coagulation and confirmed with magnetic resonance imaging. At 6 months postoperatively, improvements were seen in several areas: 1) Unified Parkinson's Disease Rating Scales II and III (UPDRS II and III) scores, 30% in off period, 38% in on period; 2) Schwab and England Scale (S&E) score, 21%; and 3) on dyskinesia, 85%. Contralateral rigidity, bradykinesia, UPDRS II and III scores, and S&E scores remained improved at 12 months. Daily dosage of levodopa requirement was reduced by 42%. Axial motor features, gait, postural stability, off period tremor, and motor fluctuation improved at 6 and 12 months but showed a decline in benefits at 18 months. Complications include 3 cases of hemiballism, of whom 2 patients recovered spontaneously but 1 died from aspiration pneumonia. One patient had asymptomatic hematoma, and 2 suffered transient postural asymmetries. We conclude that unilateral subthalamotomy results in moderate improvement in all aspects of parkinsonian features, allows reduction in the dose of levodopa required, and ameliorates drug-induced complications throughout 12-month assessments.

Effects of unilateral pallidotomy on voluntary movement, and simple and choice reaction times in Parkinson's disease

We studied the effects of unilateral pallidotomy on motor execution and reaction times in patients with moderately advanced Parkinson's disease (PD). Twelve consecutive patients (7 men, 5 women; all right-handed) underwent left-side microelectrode-guided pallidotomy. In addition to clinical rating, reaction time (RT) tests and repetitive movements of the contralesional hand/arm were carried out at baseline and 2 to 3 months after surgery while patients were on optimal medical regimens (on period). The initiation time in both simple reaction time (SRT) and choice reaction time (CRT) improved significantly after pallidotomy (P < 0.05), whereas no effect was observed on the choice processing time, which was calculated by subtracting the mean value of the onset of SRT from that of CRT. Pallidotomy resulted in significant improvement of repetitive movements such as hand pronation/supination and finger-tapping (P < 0.002, P < 0.005, respectively). Improvements in RT tests and repetitive movements suggest that pallidotomy may enhance attention and motor function. These effects are probably mediated through the pallido-thalamic-cortical neural circuitry.

Effect of bilateral stimulation of the subthalamic nucleus on parkinsonian dysarthria

Never was the effect of bilateral stimulation of the subthalamic nucleus (STN) evaluated quantitatively on all the components of speech production, that is articulation, respiration and phonation, at the same time. It is the purpose of this study which uses force measurements of the articulatory organs and acoustic analysis in 16 parkinsonian patients. With STN stimulation, reaction and movement time of the articulatory organs decreased and their maximal strength, as well as their precision increased. We also noted a large beneficial effect on voice with a significant improvement in respiratory and phonatory functions.

Randomized trial of pallidotomy versus medical therapy for Parkinson's disease

Thirty-six patients with Parkinson's disease (PD) were randomized to either medical therapy (N = 18) or unilateral GPi pallidotomy (N = 18). The primary outcome variable was the change in total Unified Parkinson's Disease Rating Scale (UPDRS) score at 6 months. Secondary outcome variables included subscores and individual parkinsonian symptoms as determined from the UPDRS. At the six month follow-up, patients receiving pallidotomy had a statistically significant reduction (32% decrease) in the total UPDRS score compared to those randomized to medical therapy (5% increase). Following surgery, patients' showed improvement in all the cardinal motor signs of PD including tremor, rigidity, bradykinesia, gait and balance. Drug-induced dyskinesias were also markedly improved. Although the greatest improvement occurred on the side contralateral to the lesion, significant ipsilateral improvement was also observed for bradykinesia, rigidity and drug-induced dyskinesias. A total of twenty patients have been followed for 2 years to assess the effect of time on clinical outcome. These patients have shown sustained improvement in the total UPDRS (p < 0.0001), "off" motor (p < 0.0001) and complications of therapy subscores (p < 0.0001). Sustained improvement was also seen for tremor, rigidity, bradykinesia, percent on time and drug-induced dyskinesias.

Pallidal neuronal activity: implications for models of dystonia

Dystonia is a neurological syndrome involving sustained contractions of opposing muscles leading to abnormal movements and postures. Recent studies report abnormally low pallidal neuronal activity in patients with generalized dystonia, suggesting hyperkinetic disorders result from underactive basal ganglia output. We examined this hypothesis in 11 patients with segmental and generalized dystonia undergoing microelectrode exploration of the internal globus pallidus (GPi) before pallidotomy or deep brain stimulation (DBS) implantation. The mean firing rates and firing patterns were compared with those in six patients with Parkinson's disease (PD). In seven patients who underwent surgery under local anesthesia, the mean GPi firing rate was 77 Hz, similar to the 74 Hz observed in the PD patients. However, in three dystonic patients under propofol anesthesia, GPi mean firing rate was much reduced (31 Hz), and the firing pattern was distinguished by long pauses in activity, as reported by others. Low-dose propofol in one other dystonia patient also seemed to suppress GPi firing. These results indicate that an abnormally low basal ganglia output is not the sine qua non of dystonia. The widely accepted pathophysiological models of dystonia that propose global decreases in basal ganglia output need to be viewed with caution in light of these findings.

Anatomic and neurophysiological methods for the targeting and lesioning of the subthalamic nucleus: Cuban experience and review

OBJECTIVE

To develop a method to place a lesion precisely in the subthalamic nucleus (STN) and evaluate its effectiveness.

METHODS

A retrospective study of targeting data collected during stereotactic planning to lesion the STN in 31 patients with Parkinson's disease and of results in more than 50 procedures was performed. The targeting method was based on computed tomographic imaging together with semimicroelectrode recording digital processing and electrical stimulation. Two statistical methods were used to correlate initial with final target coordinates and assess the efficacy of the targeting procedure.

RESULTS

The anatomic target based on computed tomographic imaging data showed electrical activity in the subthalamus in the first pass in 82% of the procedures. In the remaining 18%, the STN was an average of 1.93 mm away from the nearest trajectory that recorded the STN (range, 1.41-2.24 mm). The average number of trajectories per procedure was 7.2; the location of the first trajectory relative to the center of the nucleus determined by electrical and physiological means (P < 0.01, analysis of variance, Student's t test) was as follows: in the lateral direction, 1.25 +/- 1.15 mm; in the anteroposterior direction, 1.53 +/- 1.31 mm; and in the vertical direction, 0.67 +/- 0.51 mm. The average number of tracts necessary to lesion the STN was two.

CONCLUSION

The combination of computed tomographic imaging, semimicroelectrode recording, and microstimulation provides an effective method to identify the STN lesion in parkinsonian patients. The method used for anatomic localization and electrophysiological mapping of the subthalamus was found to be effective in reaching the sensorimotor region of the nucleus. We carried out an accurate determination of the subthalamus location and its volume in the lesioning.

Parkinson's Disease: Surgical Options

Surgical therapy for Parkinson's disease (PD) has been a treatment option for over 100 years. Advances in the knowledge of basal ganglia physiology and in techniques of stereotactic neurosurgery and neuroimaging have allowed more accurate placement of lesions or "brain pacemakers" in the sensorimotor regions of target nuclei. This, in turn, has led to improved efficacy with fewer complications than in the past. Currently, bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) or the internal segment of the globus pallidus (GPi) is the preferred option (and is approved by the US Food and Drug Administration) for the surgical treatment of PD. The most important predictors for outcome for DBS for PD are patient selection and electrode location. Patients should have a documented preoperative improvement from dopaminergic medication of at least 30% in the patient's Unified Parkinson's Disease Rating Scale motor disability scores. A levodopa challenge may be needed to document the best "on" state. Dementia or active cognitive decline must be excluded. Active psychiatric disease should be treated preoperatively. Patients should be motivated, with good support systems, and committed to the postoperative management of DBS therapy. Deep brain stimulation should be considered when the patient begins to experience dyskinesia and on-off fluctuations despite optimal medical therapy. Deep brain stimulation is not a good option at the final stages of the disease because of the increased incidence of dementia and severe comorbidity. The DBS electrode should be placed in the sensorimotor region of the GPi or STN. Subthalamic nucleus and GPi DBS can improve all motor aspects of PD, as well as predictable "on" time, without dyskinesia or fluctuations. On average, STN DBS results in a greater reduction of dopaminergic medication compared with GPi DBS. Because of the smaller size of the target region, the pulse generator battery life is longer with STN then with GPi DBS. Deep brain stimulation programming is a skill that is readily learned and may be required of all neurologists in the future. Emerging surgical therapies are restorative, and they aim to replace or regenerate degenerating dopaminergic neurons. These include embryonic mesencephalic tissue transplantation, human embryonic stem cell transplantation, and gene-derived methods of intracerebral implantation of growth factors and dopamine- producing cell lines. It will be important to determine whether DBS, if performed before the onset of motor response complications to medical therapy, may prevent this stage of disease altogether or delay it for a significant period of time. The same question applies to the future with restorative therapy.

Cognitive effects of unilateral posteroventral pallidotomy: a 4-year follow-up study

We assessed the long-term neuropsychological effects of unilateral posteroventral pallidotomy in Parkinson's disease. Eleven Parkinson's disease patients, from an original cohort of 15 consecutive patients who underwent pallidotomy, were evaluated. A neuropsychological battery was administered to each patient before (3 days) and after (3 months and 4 years) surgery during the effects of levodopa. The following tests were administered: Rey's Auditory-Verbal Learning Test, Visual Associative Learning test from the Wechsler Memory Scale-Revised, Luria's motor alternation, Benton's Judgment of Line Orientation, Trail Making, phonetic verbal fluency, Stroop test, Petrides' working memory tasks, Beck's depression questionnaire and the Maudsley obsessional-compulsive inventory. In the 3-month postoperative assessment, there was a significant worsening in phonetic verbal fluency and an improvement in Benton's Judgment of Line Orientation test. In the 4-year follow-up assessment, phonetic verbal fluency and Benton's Judgment of Line Orientation test returned to baseline scores. Although there was no significant difference between pre- and postsurgical scores for long-term visual associative memory, there was a significant deterioration between 3-month and 4-year follow-up performances. Our results suggest that unilateral posteroventral pallidotomy may produce transient changes in prefrontal and visuospatial functions, but there is no evidence of permanent neuropsychological effects.

Surgical complications in patients with Parkinson's disease after posteroventral pallidotomy

OBJECTIVE

To investigate the potential operative morbidity in posteroventral pallidotomy (PVP) for patients with Parkinson's disease.

METHODS

We designed a retrospective study that included 796 consecutive patients (mean age, 64.9 yr; male, 559; female, 237) with Parkinson's disease. All PVPs (simultaneous bilateral PVP, n = 272; sequential bilateral PVP, n = 88; unilateral PVP, n = 436) were performed during a 7-year period. The total number of operations was 884, and the number of PVP procedures was 1156. In 108 patients, ventral intermediate nucleus thalamotomy was performed simultaneously.

RESULTS

The overall complication rate, including temporary problems, was 15.3% of 884 operations. Permanent complications occurred in 3.6% of total operations. Intracranial hemorrhage occurred in 24 operations (2.7%). In seven of them, the patients required craniotomy and hematoma evacuation and sustained a disabling motor deficit (0.8%). Intracranial hemorrhage occurred more often in patients who underwent microelectrode recording and had a history of chronic hypertension. Hemiparesis without intracranial hematoma occurred in 12 operations (1.4%). Microelectrode recording was a risk factor for postoperative hemiparesis without hemorrhage. In 19 operations (2.1%), patients developed a partial visual field deficit. Speech disturbance after surgery was observed in 23 operations (2.6%) but resolved in 17 by 1 week after surgery. In 55 operations (6.2%), patients developed postoperative confusion. This occurred more often in elderly patients and those with advanced disease. In 17 operations (1.9%), patients required observation in the intensive care unit because of postoperative hypotension.

CONCLUSION

Complications from stereotactic pallidotomy were not frequent. However, the residual symptoms from complications can be serious in many cases.

The fluctuating Parkinsonian patient--clinical and pathophysiological aspects

Although levodopa-related motor response complications remain challenging from a pathophysiological and therapeutic standpoint, major advances have been made in the last decade, supporting the development of several promising drugs. Eventually, these drugs may help us to prevent, alleviate, or even "deprime" these frequent and disabling complications. Knowledge of the basic mechanisms and hypotheses underlying this fascinating conversion in the parkinsonian brain allows neurologists to understand the rationale behind emerging treatment strategies.

Neuropsychology for movement disorders neurosurgery

The neuropsychologist plays a crucial role in three phases of the neurosurgical treatment of movement disorder patients, namely screening, outcome evaluation and research. In screening patients, the differential diagnosis of dementia, impact of depression or other psychiatric conditions, and the influence of disease and medication-induced symptoms on cognitive performance must be determined. Postoperatively, systematic evaluations elucidate the cognitive costs or benefits of the procedure. The neuropsychologist is then able to provide feedback and counselling to the professional staff, patient and family to inform management strategies. Neuropsychologists also study alteration of cognitive processing due to lesions or stimulation, which, in tandem with functional imaging, shed light on plasticity in cortical and subcortical processing.

A novel skilled-reaching impairment in paw supination on the "good" side of the hemi-Parkinson rat improved with rehabilitation

Parkinson's disease is characterized by tremor, rigidity, bradykinesia, and postural abnormalities ascribed to the loss of nigrostriatal dopamine (DA). Symptoms similar to the human condition can be produced in the rat by DA-depleting 6-hydroxydopamine injections made into the nigrostriatal system. After a unilateral lesion, the rat symptoms include sensory and motor impairments and turning biases reflecting motor abnormalities to the contralateral-to-depletion side of the body. In addition, a number of studies on skilled reaching report impairments in the use of the ipsilateral limb. It is suggested that the ipsilateral deficit is secondary to the contralateral motor impairments however. Here we re-examine how rats with unilateral DA depletion use their ipsilateral limb for skilled reaching for food. We provide the first description of an impairment on the ipsilateral-to-depletion side of the body of the rat and the first demonstration of amelioration of the defect using behavioral therapy. Video analysis of rats reaching for single pellets of food with the ipsilateral limb revealed that, although limb advancement and food grasping were normal, paw supination and food release to the mouth were impaired. Consequently, the animals were unable to transport a grasped food pellet to the mouth. Behavioral therapy, consisting of training in a simpler reaching task, strikingly lessened the impairment and improved reaching movements to the point that the rats could transport the food to the mouth. The results are discussed in relation to possible causes of the ipsilateral impairment, its treatment, and to relevant research on human Parkinson patients, indicating that they display bilateral improvements after unilateral treatments.

Analysis of complications of radiofrequency pallidotomy

OBJECTIVE

To systematically report the complications of pallidotomy and to tentatively determine the incidences of complications of pallidotomy, possible influencing factors, and the acceptability of symptomatic hemorrhage rates for microelectrode-guided pallidotomy.

METHODS

Clinical events were analyzed for 1116 patients with Parkinson's disease who underwent microelectrode-guided pallidotomies at our center. Complications included visual field deficits, weakness, fatigue, hypersomnia, drooling, dysphagia, speech disorders, hiccups, hemorrhage, seizures, apraxia, coma, infection, mental confusion, and impaired memory. Complication rates for bilateral pallidotomy and double-lesion groups were compared with those for unilateral pallidotomy and single-lesion groups, respectively.

RESULTS

Among the total of 1116 patients, the incidences of visual field deficits, weakness, fatigue, hypersomnia, drooling, dysphagia, and speech disorders were 0.4, 4.2, 19.9, 12.4, 7.0, 3.7, and 11.9%, respectively. Symptomatic hemorrhage was observed for 17 patients, apraxia for 3 patients, coma for 2 patients, mental confusion for 24 patients, and impaired memory for 18 of the 1116 patients. The incidences of fatigue, speech disorders, drooling, dysphagia, and hypersomnia were 18.1, 10.3, 5.2, 2.4, and 11.6%, respectively, in the unilateral pallidotomy group and 34.9, 25.5, 22.6, 14.2, and 17.0%, respectively, in the staged pallidotomy group. Of the three patients who underwent simultaneous bilateral pallidotomies (all <50 yr of age), all developed severe fatigue and two exhibited drooling and dysphagia. The incidences of weakness, fatigue, speech disorders, drooling, dysphagia, and hypersomnia were 8.7, 30.4, 18.8, 7.2, 2.9, and 20.3%, respectively, in the double-lesion group and 3.2, 17.2, 9.7, 5.0, 2.3, and 11.5%, respectively, in the single-lesion group.

CONCLUSION

Staged bilateral pallidotomy should be carefully evaluated before decision-making, whereas simultaneous bilateral pallidotomy is undesirable. Our study suggests that the size of the final lesion should be limited, to minimize the risks of complications. The incidence of symptomatic hemorrhage in microelectrode-guided pallidotomy is low and acceptable, because of the benefits of microelectrode-guided pallidotomy.

Motor circuitry re-organization after pallidotomy in Parkinson disease: a neurophysiological study of the bereitschaftspotential, contingent negative variation, and N30

The aim of the study was to evaluate the reorganization changes in the motor circuitry of the basal ganglia following unilateral posteroventral pallidotomy in Parkinson disease (PD) patients using neurophysiological paradigms. Eight advanced PD patients received a neurophysiological battery 2 months prior and 6 months after unilateral pallidotomy. Examinations were all performed in the practically defined "off" situation. Bereitschaftspotential (BP) and N30 were recorded for each hand alternately. Contingent negative variation (CNV) was obtained using a visual Go/no-Go paradigm. ANOVAs (electrode position; surgery) were applied for BP and CNV results. N30 data were analyzed using Wilcoxon matched-pair tests. A significant increase in amplitude of the late component (NS') of the BP was evidenced with patient performing with the hand contralateral to pallidotomy. No significant amplitude differences were found in CNV after surgery in any lead, or in any of the time windows tested. A trend toward significance was observed corresponding to a postsurgical numerical increase in amplitude of the N30 peak in the hand contralateral to pallidotomy. These results suggest that neurophysiological changes after pallidotomy are mainly in the last stages of movement preparation and execution.

Localization of clinically effective stimulating electrodes in the human subthalamic nucleus on magnetic resonance imaging

OBJECT

The authors sought to determine the location of deep brain stimulation (DBS) electrodes that were most effective in treating Parkinson disease (PD).

METHODS

Fifty-four DBS electrodes were localized in and adjacent to the subthalamic nucleus (STN) postoperatively by using magnetic resonance (MR) imaging in a series of 29 patients in whom electrodes were implanted for the treatment of medically refractory PD, and for whom quantitative clinical assessments were available both pre- and postoperatively. A novel MR imaging sequence was developed that optimized visualization of the STN. The coordinates of the tips of these electrodes were calculated three dimensionally and the results were normalized and corrected for individual differences by using intraoperative neurophysiological data (mean 5.13 mm caudal to the midcommissural point [MCP], 8.46 mm inferior to the anterior commissure-posterior commissure [AC-PC], and 10.2 mm lateral to the midline). Despite reported concerns about distortion on the MR image, reconstructions provided consistent data for the localization of electrodes. The neurosurgical procedures used, which were guided by combined neuroimaging and neurophysiological methods, resulted in the consistent placement of DBS electrodes in the subthalamus and mesencephalon such that the electrode contacts passed through the STN and dorsally adjacent fields of Forel (FF) and zona incerta (ZI). The mean location of the clinically effective contacts was in the anterodorsal STN (mean 1.62 mm posterior to the MCP, 2.47 mm inferior to the AC-PC, and 11.72 mm lateral to the midline). Clinically effective stimulation was most commonly directed at the anterodorsal STN, with the current spreading into the dorsally adjacent FF and ZI.

CONCLUSIONS

The anatomical localization of clinically effective electrode contacts provided in this study yields useful information for the postoperative programming of DBS electrodes.

Surgical therapy for Parkinson's disease

Surgical therapies for Parkinson's disease (PD) are now being performed with increasing frequency due to the limitations of conventional dopaminergic therapies, improvements in operative procedures, and increased information on the organization of the basal ganglia in normal and pathologic conditions. Ablation procedures have now been largely replaced with deep brain stimulation, which permits benefits to be obtained without the need to make a destructive brain lesion. Several studies now demonstrate the value of stimulating the subthalamic nucleus or the globus pallidus pars interna in patients with advanced PD. Nonetheless, there are limitations associated with these procedures and benefits do not exceed those obtained with levodopa, albeit with reduced motor complications. Fetal transplantation remains an experimental procedure that has shown limited benefits in a double-blind trial and is complicated by persistent dyskinesia. Stem cell, trophic factor, and gene therapy approaches are promising and are currently under intensive investigation.

Subthalamotomy for advanced Parkinson disease

Object. The aim of this study was to determine if subthalamotomy is effective in treating advanced Parkinson disease (PD).

Methods. The authors performed microelectrode mapping—guided stereotactic surgery on the subthalamic nucleus in eight patients with PD. Lesioning was performed using radiofrequency heat coagulation and confirmed with magnetic resonance imaging. Three patients who underwent unilateral and four with bilateral subthalamotomy were evaluated for up to 18 months according to the Unified PD Rating Scale (UPDRS). One patient who underwent unilateral subthalamotomy died 6 months postsurgery.

At 3 months into the “off” period after surgery, there were significant improvements in contralateral bradykinesia (p < 0.0002), rigidity (p < 0.0001), tremor (p < 0.01), axial motor features (p < 0.02), gait (p < 0.03), postural stability (p < 0.03), total UPDRS scores (p < 0.03), and Schwab and England scores (p < 0.04). The benefits were sustained at 6, 12, and 18 months, except for the improvement in tremor. At 12 months into the “on” period, significant benefits were present for motor fluctuation (p < 0.04), on dyskinesia (p < 0.006), off duration (p < 0.05), total UPDRS score (p < 0.02), and contralateral tremor (p < 0.05). Benefits for motor fluctuation, off duration, and off-period tremor were lost after the 18-month follow-up period. The levodopa requirement was reduced by 66% for the unilateral and 38% for the bilaterally treated group. Bilateral subthalamotomy offered more benefits than did unilateral surgery for various parkinsonian features in both the on and off periods. Three patients suffered hemiballismus, two recovered spontaneously, and one died of aspiration pneumonia after discontinuation of levodopa.

Conclusions. These findings indicate that subthalamotomy can ameliorate the cardinal symptoms of PD, reduce the dosage of levodopa, diminish complications of the drug therapy, and improve the quality of life.

Novel physical treatments for the management of neuropsychiatric disorders

OBJECTIVE

To briefly describe the novel non-drug physical interventions currently in use in the investigation and treatment of neuropsychiatric disorders regarding their efficacy and potential future applications.

METHODS

A systematic review of the literature concerning transcranial magnetic stimulation (TMS), deep brain stimulation (DBS), vagus nerve stimulation (VNS) and neurosurgery for mental disorders (NMD) was conducted using Medline and literature known to the authors.

RESULTS

A summary of each procedure is provided giving a succinct overview of efficacy, current applications and possible future indications.

CONCLUSION

Novel and innovative physical interventions are currently being used to study brain function in health and disease. In particular, TMS has quickly established itself as a useful investigational tool and is emerging as a possible antidepressant therapy. Similarly, VNS has been applied successfully in the management of intractable epilepsy and is undergoing evaluation in the management of patients with treatment-resistant depression. DBS has shown significant promise in the treatment of Parkinson's disease and may have use in the management of obsessive-compulsive disorder. Finally, neurosurgical procedures for the treatment of mental disorders have been sufficiently refined to stage a comeback, although rigorous scientific study of their efficacy and indications is still necessary.

Localisation of the subthalamic nucleus using Radionics Image Fusion and Stereoplan combined with field potential recording. A technical note

Subthalamic nucleus stimulation is an effective therapy for alleviating parkinsonian tremor, rigidity and bradykinesia. Although microelectrode recording is said to be essential for accurate targeting, this often prolongs the operation and the multiple recording tracts required may increase the incidence of complications, particularly haemorrhage. We describe a technique for implantation of deep brain electrodes in the subthalamic nucleus using MRI/CT fusion for anatomical localisation followed by bipolar recording of focal field potentials via the implanted stimulating electrode for neurophysiological confirmation of the stimulation site. The technique is effective, safe and requires much less time, and can be used as an alternative method to microelectrode recording.

Metabolic alterations in Parkinson's disease after thalamotomy, as revealed by 1H MR spectroscopy

OBJECTIVE

To determine, using proton magnetic resonance spectroscopy (1H MRS) whether thalamotomy in patients with Parkinson's disease gives rise to significant changes in regional brain metabolism.

MATERIALS AND METHODS

Fifteen patients each underwent stereotactic thalamotomy for the control of medically refractory parkinsonian tremor. Single-voxel 1H MRS was performed on a 1.5T unit using a STEAM sequence (TR/TM/TE, 2000/14/20 msec), and spectra were obtained from substantia nigra, thalamus and putamen areas, with volumes of interest of 7-8 ml, before and after thalamotomy. NAA/Cho, NAA/Cr and Cho/Cr metabolite ratios were calculated from relative peak area measurements, and any changes were recorded and assessed.

RESULTS

In the substantia nigra and thalamus, NAA/Cho ratios were generally low. In the substantia nigra of 80% of patients (12/15) who showed clinical improvement, decreased NAA/Cho ratios were observed in selected voxels after thalamic surgery (p < 0.05). In the thalamus of 67% of such patients (10/15), significant decreases were also noted (p < 0.05).

CONCLUSION

Our results suggest that the NAA/Cho ratio may be a valuable criterion for the evaluation of Parkinson's disease patients who show clinical improvement following surgery. By highlighting variations in this ratio, 1H MRS may help lead to a better understanding of the pathophysiologic processes occurring in those with Parkinson's disease.

Unilateral and bilateral pallidotomy for idiopathic Parkinson's disease: a case series of 115 patients

Lesioning of the internal pallidum is known to improve the symptoms of idiopathic Parkinson's disease (PD) and alleviate dyskinesia and motor fluctuations related to levodopa therapy. The benefit obtained contralateral to a single lesion is insufficient in some cases when symptoms are bilaterally disabling. However, reports of unacceptably high rates of adverse effects after bilateral pallidotomy have limited its use in such cases. We report on the outcome of unilateral (UPVP) and bilateral (BPVP) posteroventral pallidotomy in a consecutive case series of 115 patients with PD in the United Kingdom and Australia. After 3 months, UPVP resulted in a 27% reduction in the off medication Part III (motor) Unified Parkinson's Disease Rating Scale score and abolition of dyskinesia in 40% of cases. For BPVP, these figures were increased to 31% and 63%, respectively. Follow-up of a smaller group to 12 months found the motor scores to be worsening but benefit to dyskinesia and activities of daily living was maintained. Speech was adversely affected after BPVP, although the change was small in most cases. Unilateral and bilateral pallidotomy can be performed safely without microelectrode localisation. Bilateral pallidotomy appears to be more effective, particularly in reducing dyskinesia; in our experience, the side effects have not been as high as reported by other groups.

A metaanalysis comparing the results of pallidotomy performed using microelectrode recording or macroelectrode stimulation

OBJECT

There is an active debate regarding whether pallidotomy should be performed using macroelectrode stimulation or the more sophisticated and expensive method of microelectrode recording. No prospective, randomized trial results have answered this question, although personnel at many centers claim one method is superior. In their metaanalysis the authors reviewed published reports of both methods to determine if there is a significant difference in clinical outcomes or complication rates associated with these methods.

METHODS

A metaanalysis was performed with data from reports on the use of unilateral pallidotomy in patients with Parkinson disease (PD) that were published between 1992 and 2000. A Medline search was conducted for the key word "pallidotomy" and additional studies were added following a review of the references. Only those studies dealing with unilateral procedures performed in patients with PD were included. Papers were excluded if they described a cohort smaller than 10 patients or a follow-up period shorter than 3 months or included cases that previously had been reported. The primary end points for outcome were the percentages of improvement in dyskinesias and in motor scores determined by the Unified PD Rating Scale (UPDRS). Complications were categorized as mortality, intracranial hemorrhage, visual deficit, speech deficit, cognitive decline, weakness, and other. There were no significant differences between the two methods with respect to improvements in dyskinesias (p = 0.66) or UPDRS motor scores (p = 0.62). Microelectrode recording was associated with a significantly higher (p = 0.012) intracranial hemorrhage rate (1.3 +/- 0.4%), compared with macroelectrode stimulation (0.25 +/- 0.2%).

CONCLUSIONS

In reports of patients with PD who underwent unilateral pallidotomy, operations that included microelectrode recording were associated with a small, but significantly higher rate of symptomatic intracranial hemorrhage; however, there was no difference in postoperative reduction of dyskinesia or bradykinesia compared with operations that included macroelectrode stimulation.

Chronic anterior thalamus stimulation for intractable epilepsy

PURPOSE

A significant number of patients with epilepsy remain poorly controlled despite antiepileptic medication (AED) treatment and are not eligible for resective surgery. Novel therapeutic methods are required to decrease seizure burden in this population. Several observations have indicated that the anterior thalamic region plays an important role in the maintenance and propagation of seizures. We investigated neuromodulation of the anterior thalamus by using deep-brain stimulation (DBS) in patients with intractable seizures.

METHODS

Five patients with medically refractory epilepsy underwent stereotactic placement of and received stimulation through bilateral DBS electrodes in the anterior thalamus.

RESULTS

Treatment showed a statistically significant decrease in seizure frequency, with a mean reduction of 54% (mean follow-up, 15 months). Two of the patients had a seizure reduction of > or =75%. No adverse effects were observed after DBS electrode insertion or stimulation. Unexpectedly, the observed benefits did not differ between stimulation-on and stimulation-off periods.

CONCLUSIONS

DBS of the anterior thalamus is a safe procedure and possibly effective in patients with medically resistant seizures.

The globus pallidus, deep brain stimulation, and Parkinson's disease

Parkinson's disease (PD) is caused by the degeneration of the dopaminergic neurons in the substantia nigra. Loss of dopaminergic innervation leads to hyperactivity in the internal segment of the globus pallidus (GPi), the main output nucleus of the basal ganglia and to a profound disturbance in the function of motor circuits. Lesions of the GPi (or in its upstream modulator, the subthalamic nucleus) can greatly improve the motor symptoms of PD presumably by reducing this pathological activity. Paradoxically, high-frequency electrical stimulation of the GPi (deep brain stimulation, DBS) mimics the effects of pallidotomy and has become an accepted therapeutic technique. The mechanisms underlying the beneficial effects of pallidal DBS are not known. Various mechanisms that might account for inhibiting or disrupting the pathological pallidal outflow by high-frequency DBS have been proposed ranging from depolarization block to stimulation-evoked release of GABA, and these are discussed.

Treatment results: Parkinson's disease

Deep brain stimulation (DBS) is a neurosurgical treatment of Parkinson's disease that is applied to three targets: the ventral intermediate nucleus of the thalamus (Vim), the globus pallidus internas (GPi) and the subthalamic nucleus (STN). Vim DBS mainly improves contralateral tremor and, therefore, is being supplanted by DBS of the two other targets, even in patients with tremor dominant disease. STN and GPi DBS improve off-motor phases and dyskinesias. There is little comparative data between these procedures. The magnitude of the motor improvement seems more constant with STN than GPi DBS. STN DBS allows a decrease in antiparkinsonian drug doses and consumes moderate current. These advantages of STN over GPi DBS are offset by the need for more intensive postoperative management. The DBS procedure has the unique advantage of reversibility and adjustability over time. Patients with young-onset Parkinson's disease suffering from levodopa-induced motor complications but still responding well to levodopa and who exhibit no behavioral, mood, or cognitive impairment benefit the most from STN DBS. Adverse effects more specific of the DBS procedure are infection, cutaneous erosion, and lead breaking or disconnection. Intracranial electrode implantation can induce a hematoma or contusion. Most authors agree that the benefit to risk ratio of DBS is favorable.

Complications of deep brain stimulation surgery

Currently, DBS is a commonly performed surgery for treatment of movement disorders, especially Parkinson's disease. Although nonablative and minimally invasive, this procedure may give rise to many complications and side effects, some of which are neither reversible nor adaptable. This study reviews the potential complications of DBS along the entire path of this procedure, from patient selection through the postoperative period. Although intraoperative complications such as paralysis and hematoma are rare, other serious complications due to the hardware, such as lead fracture, dislocation, and infection, are not uncommon. Complications or side effects as a result of chronic stimulation itself may be the most common. It is concluded that every member of the surgical team, including the referring neurologist, has an important role in the avoidance of such complications. Proper and careful patient selection, matching each patient to the specific DBS procedure appropriate for his/her symptom profile and suitable for his/her social and cognitive condition, along with experienced and careful intraoperative surgical routine, may be the best way to prevent the complications of DBS procedures.