Opposite motor effects of pallidal stimulation in Parkinson's disease

Relationship of lesion location to clinical outcome following microelectrode-guided pallidotomy for Parkinson's disease

The purpose of this study was to examine the relationship between lesion location and clinical outcome following globus pallidus internus (GPi) pallidotomy for advanced Parkinson's disease. Thirty-three patients were prospectively studied with extensive neurological examinations before and at 6 and 12 months following microelectrode-guided pallidotomy. Lesion location was characterized using volumetric MRI. The position of lesions within the posteroventral region of the GPi was measured, from anteromedial to posterolateral along an axis parallel to the internal capsule. To relate lesion position to clinical outcome, hierarchical multiple regression analysis was used. The variance in outcome measures that was related to preoperative scores and lesion volume was first calculated, and then the remaining variance attributable to lesion location was determined. Lesion location along the anteromedial-to-posterolateral axis within the GPi influenced the variance in total score on the Unified Parkinson's Disease Rating Scale in the postoperative 'off' period, and in 'on' period dyskinesia scores. Within the posteroventral GPi, anteromedial lesions were associated with greater improvement in 'off' period contralateral rigidity and 'on' period dyskinesia, whereas more centrally located lesions correlated with better postoperative scores of contralateral akinesia and postural instability/gait disturbance. Improvement in contralateral tremor was weakly related to lesion location, being greater with posterolateral lesions. We conclude that improvement in specific motor signs in Parkinson's disease following pallidotomy is related to lesion position within the posteroventral GPi. These findings are consistent with the known segregated but parallel organization of specific motor circuits in the basal ganglia, and may explain the variability in clinical outcome after pallidotomy and therefore have important therapeutic implications.

Surgical options in Parkinson's disease

Surgical treatments for Parkinson's disease (PD) have again become important adjuncts of care in these patients. We have learned much from the thousands of lesions performed historically, and are now advancing the entire field of movement disorder surgery to new levels of sophistication and understanding. The last 5 years have seen more precise and reliable lesioning and the arrival of multiple sites of intervention afforded by recent developments in deep brain stimulators. Because patients typically derive significant benefit in their quality of life from these procedures, while undergoing little risk, the surgical options should be carefully considered for selected PD patients.

Bilateral high-frequency stimulation of the internal globus pallidus in advanced Parkinson's disease

We report here the results of an open prospective study in 9 patients suffering from severe Parkinson's disease with on/off fluctuations and restricted off-period mobility, who underwent bilateral implantation of stimulating electrodes in the internal pallidum. At 3-month follow-up, the total Unified Parkinson's Disease Rating Scale (UPDRS) motor score in the medication-off state was reduced from 54.1+/-14.8 to 23.9+/-11.7 (44.2%) when stimulation was turned on. Comparison of UPDRS subscores revealed significant improvements for tremor, rigidity, bradykinesia, gait and posture, and dyskinesias. The results of the clinical scoring could be confirmed by significant changes in the quantitative assessment of hand function and walking. Bilateral pallidal stimulation reduced the amount and severity of on/off fluctuations. Additional follow-up at 6 months (n=6), 9 months (n=6), and 12 months (n=4) did not show a decline in effectiveness of stimulation. There was no permanent morbidity associated with the procedure. A subtle reduction of verbal fluency, which was not evident to the patients, was the only cognitive side effect of the procedure in neuropsychological testing. Chronic bilateral high-frequency stimulation of the internal pallidum seems to be a neurologically safe and highly effective treatment for "off" symptoms, dyskinesias, and motor fluctuations in advanced stages of Parkinson's disease.

Treatment of tremor in Parkinson's disease by subthalamic nucleus stimulation

The recent resurgent interest in functional surgery for the treatment of Parkinson's disease (PD) has focused on the effects on akinesia and levodopa-induced dyskinesia. Stimulation of the subthalamic nucleus (STN) improves akinesia and rigidity but its effects on tremor have not been studied. The objective of this study was to assess the efficacy of STN stimulation on tremor in patients with the complete parkinsonian triad with motor fluctuations. Of 27 consecutive patients with STN stimulation (26 bilateral), 15 exhibited tremor rated at least 2/4 according to item 20 (rest tremor) of the Unified Parkinson's Disease Rating Scale (UPDRS) in at least one limb. The mean preoperative tremor score was 11.3+/-5.6 in off-drug and 1.2+/-2.4 in on-drug conditions. The postoperative tremor scores at the last follow up (from 1-12 months) were 2.2+/-2.2 off-drug/on-stimulation and 0.2+/-0.4 on-drug/on-stimulation. Both rest and action tremors were improved in all patients. The UPDRS tremor score was reduced by 80%, rigidity score by 65%, and akinesia score by 51% on average. For the three symptoms, the stimulation effect was close to that induced before surgery by a suprathreshold dose of levodopa given in the morning. STN stimulation can be considered an interesting alternative to thalamic or internal pallidal surgery even in PD patients with severe high-amplitude tremor. In keeping with electrophysiological data in monkeys rendered parkinsonian by MPTP injections, our results emphasize the importance of the oscillation of a neuronal loop involving the STN in the pathophysiology of parkinsonian tremor.

Pallidal stimulation in Parkinson's disease patients with a prior unilateral pallidotomy

OBJECTIVE

To evaluate, in a double-blind fashion, the efficacy of deep brain stimulation of the internal segment of the globus pallidus (GPi) contralateral to a previous unilateral medial pallidotomy (MP).

METHODS

This pilot study involved 4 patients with a previous MP and one previously unoperated patient unable to tolerate any antiparkinsonian drugs. One of the patients with a prior unilateral MP had two electrodes implanted in the contralateral side, one in GPi and one in Vim thalamus. Detailed neurologic assessments were performed after overnight drug withdrawal and in the drug "on" state at baseline, 1 week and 3 months (in all), and 9 and 12 months (one) with patients and evaluators blinded to the status of stimulation.

RESULTS

GPi stimulation resulted in improvements in "off-period" contralateral bradykinesia, rigidity and tremor in all patients. Dyskinesias and freezing episodes were ameliorated in one patient each but dyskinesias were transiently induced in another. The patient with GPi + Vim electrodes had complete resolution of contralateral tremor with thalamic stimulation but less benefit from acute GPi stimulation. One patient experienced a single seizure one week post-op and no other surgical complications were observed.

CONCLUSIONS

Deep brain stimulation can be applied safely and effectively in patients who have already had a pallidotomy on the contralateral side. The effect of stimulation at different sites on different symptom profiles and levodopa-induced dyskinesias requires further evaluation.

Inhibition of levodopa effects by internal pallidal stimulation

We report three patients with bilateral GPi stimulation for stage 4 Parkinson's disease (PD) with severe levodopa-induced dyskinesias (LID). In all three it was possible to completely inhibit LID using high-stimulation parameters. Parallel to complete inhibition of LID, an inhibition of the anti-akinetic effect of levodopa was observed, whereas, at the same time, rigidity was markedly improved. GPi stimulation is adaptable over time, and stimulation parameters have to be programmed according to off- and on-period motor symptoms. The main interest of stimulation is the possibility of finding a compromise between LID alleviation in on-phase without loss of the beneficial motor effects and improvement in parkinsonism in off-phase. In some patients, residual dyskinesias have to be accepted so as not to aggravate on-period motor symptoms by a presumed overinhibition of basal ganglia outflow.